HNL-Sub-4450-1
MIT-EL 76-005
Final Report
WATER TESTS FOR DETERMINING
POST-VOIDING BEHAVIOR IN THE LMFBR
by
William D. Hinkle
Energy Laboratory
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139
sponsored by
The Union Carbide Corporation, Nuclear Division
under Subcontract No. 4450 of
Contract No. W-7405-eng-26
with
The United States Energy Research and
Development Administration
June, 1976
A
ABSTRACT
The most serious of the postulated accidents considered in
the design of the Liquid Metal Cooled Fast Breeder Reactor (LMFBR)
is the Loss of Pipe Integrity (LOPI) accident. Analysis models
used to calculate the consequences of this accident assume that
once boiling is initiated film dryout occurs in the hot assembly
as a result of rapid vapor bubble growth and consequent flow
stoppage or reversal. However, this assumption has not been put
to any real test.
Once boiling is initiated in the hot assembly during an LMFBR
LOPI accident, a substantial gravity pressure difference would exist
between this assembly and other colder assemblies in the core. This
condition would give rise to natural circulation flow boiling
accompanied by pressure and flow oscillations. It is possible that
such oscillations could prevent or delay dryout and provide
substantial post-voiding heat removal. The tests described in this
report were conceived with the objective of obtaining basic information and data relating to this possibility.
To accomplish this objective a natural circulation test loop
was designed to simulate LMFBR geometry and flow conditions predicted
to exist at the time boiling is initiated in a LOPI accident. The
test loop included: (1) a vertical tube test section, (2) upper and
lower plenum.tanks, (3) an external down-commer, (4) sight flow
indicators and (5) instrumentation. The test section was an
electrically heated tube designed with a hydraulic diameter and
length similar to current LMFBR (FTR) design. The upper and lower
plenum tanks were provided with means for controlling liquid
subcooling above and below the test section. The down-commer was
large enough to eliminate down-commer hydraulics. Water at a
pressure of 1 atmosphere was used to simulate sodium. Sight flow
indicators were provided to observe flow conditions at the test
section inlet and exit. Instrumentation was provided to measure
test section pressures, inlet and exit temperatures, tube wall
temperatures, heat flux and oscillation frequencies.
Steady state tests were conducted for subcooled flow boiling,
saturated flow boiling, CHF and post CHF conditions. Subcooled
flow boiling was observed for heat fluxes below 1 x 104 BTU/hr ft2 .
For this condition, both pressure oscillations and temperature
oscillations at the heated surface were observed; but the pressure
oscillations were not observed continuously. Saturated flow
boiling was observed for heat fluxes between 3 x 104 BTU/hr ft2
and CHF. For this condition, pressure oscillations were observed
continuously. As the CHF condition was approached, a periodic
downward expansion of vapor from the heated section was observed at
the bottom sight flow indicator and the flow regime appeared to be
annular at the top sight flow indicator. CHF was observed at the
top of the heated section when the heat flux reached 6.4 x 104
BTU/hr ft2 , but rewetting occurred after a few seconds. As the
heat flux was increased further, the maximum surface temperature
reached before rewetting increased; until, at a heat flux of 7.15 x
104 BTU/hr ft2 , the maximum temperature exceeded 9000 F and rewetting
no longer occurred.
A transient test was conducted for a post CHF condition. The.
heat flux was 7.3 x 104 BTU/hr ft2 . The oscillations observed under
steady state conditions developed within a few seconds after the
power was turned on. The equilibrium tube wall temperature upstream
of the CHF location was reached in 10 seconds. The equilibrium tube
wall temperature at the CHF location was reached in about 135 seconds.
A similarity analysis was done in order to scale the test results
to LMFBR LOPI conditions. The results of this analysis indicate that
the CHF for the LMFBR (FTR) would be at least 6 x 104 BTU/hr ft2 .
This corresponds to a critical average linear power for the hot
assembly of 1.06 kw/ft compared to an estimated 2.55 to 5.1 kw/ft being
transferred to the coolant at the time boiling begins during a LOPI
accident. On the basis of this analysis, the results of the water
tests indicate that CHF would occur. But, this conclusion is
conservative for a number of reasons and further experimental work
on a more prototypical system is suggested.
ACKNOWLEDGEMENTS
The tests described herein were supported by the Union
Carbide Corporation, Nuclear Division under Subcontract 4450 of
Contract No. W-7405-eng-26 with the United States Energy Research
and Development Administration.
Prof. P. Griffith initially suggested the tests and gave
generously of his time to discuss their design and interpretation.
Shop facilities, laboratory space and miscellaneous parts
of the experimental equipment were provided by the MIT Department
of Mechanical Engineering.
Mr. J. Caloggero, Mr. F. Johnson and Mr. A. Crandall were
most helpful in discussing the-design of the test loop and were
responsible for its fabrication and construction.
The draft report was reviewed by the ERDA LMFBR Loss of
Pipe Integrity Working Group.
Members of this group provided a
number of constructive comments and suggestions that were
incorporated into the final report.
Ms. Marsha Levine did an excellent job of typing both the
draft and final reports.
I wish to express my thanks to all concerned.
TABLE OF CONTENTS
Section
I.
II.
III.
Page
INTRODUCTION
A.
Background......... · · · ·.·.·.· · · · ·. ·
B.
Objective ..........
I -1
I-3
.........................
APPARATUS
II -1
A.
Design Basis
B.
Similarity Analysis
C.
Description of Test Loop ..................
..
............
II -3
II-14
1.
2.
General ...............................
Test Section .......
II-14
II-18
3.
4.
Sight Flow Indicators .
Plenum Tanks ............
5.
Down-commer ................. ......... II-22
6.
Power Supply ...........................
II-22
7.
Instrumentation ......
......
....
I...11-19
......
II-19
........
II-24
TEST PROCEDURES
A.
B.
C.
D.
General................. ..................III - 1
Steady State Tests...... ..................III -1
Transient Tests......... .................. III - 2
Data Reduction.......... ..................III - 3
1.
2.
Thermocouple Data.. .................. III -3
Pressure Transducer Data ............. III - 4
3.
Test Section Power DIMeasurement .......III- 5
4.
Calculation of Flow from Energy
Balance ............
......III
5.
Calculation of Heat Transfer
Coefficients .......
*---.-----..
IV.
·
- 6
......III - 6
DATA AND OBSERVATIONS
A.
Steady State Tests ....................... IV - 1
1.
Onset of Subcooled Boiling (Run #1) ...IV- 1
-1
2.
Subcooled Boiling (Run #2) .IV
3.
Saturated Boiling (Run #3) ...........IV-ll
IV-18
4.
Onset of CHF (Run #4) .................
Section
Page
B.
Transient Tests........................ ...IV-22
1.
2.
V.
Step Increase in Heat Flux to
Beyond CHF (Run #5)...................IV-22
Liedenfrost Temperature (Run #6)......IV-22
ANALYSIS AND DISCUSSION
A.
Analysis and Discussion of Tests .......
1.
2.
Flow-Pressure Drop Characteristics
of Test Loop ...................... ... V- 1
Subcooled Boiling (Runs #1 and #2)....V - 6
Summary of Principal Results
b.
Analysis of Temperature Data .....V - 8
Analysis of Flow and Pressure
Information .................. ....V-14
c.
3.
Bulk Boiling (Run #3)..................V-17
a.
Summary of Principal Results ....V-17
b.
c.
4.
V-19
Analysis of Temperature Data
Discussion of Pressure Oscillation Data and Observations .....V-21
Onset of CHF (Run #4)..................V-23
a.
Summary of Principal Results.. ....
V-23
b.
Analysis and Discussion of
Temperature Data.............. ...
c.
5.
... .V-6
a.
V-24
Discussion of CHF Mechanism... ....V-29
Transient Tests (Runs #5 and #6).......V-29
a.
Step Increase in Heat Flux
to Beyond CHF (Run #5)....... .....V-29
b.
B.
Liedenfrost Temperature (Run
#6).......................... .....V-30
.....
V-30
Analysis of LMFBR .................
1.
2.
3.
4.
5.
Flow-Pressure Drop Characteristics
of Reactor Loop................... .....V-30
Subcooled Boiling................. .....V-35
Bulk Boiling...................... .....V-35
6
Onset of CHF...................... .....
V -3 9
Beyond CHF........................
.
.
Section
VI.
Page
CONCLUSIONS AND RECOMMENDATIONS
.......................
1.
Conclusions
2.
..........
Recommendations
REFERENCES
NOMENCLATURE
.............
VI - 1
I- 8
LIST OF FIGURES
Figure
Page
II-1
Assumed Reactor/Test Loop Geometry........... .. II
II-2
Control Volume Used for Similarity Analysis
(Section II.A.2) ...........................
II-3
..-II-
Schematic Diagram Relating Lland
L 2 6 to L 1 ,
L2 , LH and LB
.....................
..
-
2
4
.II-10
II-4
Schematic of Water Test Apparatus.............. II-15
II-5
Sight Flow Indicator ........................... II-20
II-6
Upper and Lower Plenum Tanks ........
II-7
Schematic of Hydraulic System and Heat
Exchangers Used to Control Upper and Lower
Plenum Temperatures
.
.................. II-23
II-B
Detail of Test Section Showing Power Lug
Connection and Insulated Flange................ II-25
II-9
Schematic of Loop Instrumentation.............. II-26
II-10
Location of Pressure and Temperature
Measurements................................... II-27
IV-1A
Pressure Traces from XY Recorder for Run #1
(Onset of Subcooled Boiling) ..................
........ II-21
IV- 3
IV-lB
Temperature Traces from XY Recorder for
Run #1 (Onset of Subcooled Boiling) ............ IV- 4
IV-2A
Pressure Traces from XY Recorder for Run #2
(Subcooled Boiling - Taken on First Day Just
After Completing Run #1)....................... IV- 6
IV-2B
Temperature Traces from XY Recorder for
Run #2 (Subcooled Boiling - Taken on First
Day Just After Completing Run #1).............. IV- 7
IV-2C
Pressure and Temperature Traces from XY
Recorder for Run #2 (Subcooled Boiling Taken on Second Day Less Than 10 Minutes
After Heating Up Test Section) ....
.........IV- 8
IV-2D
Pressure Traces from XY Recorder for Run #2
(Subcooled Boiling - Taken on Second Day
20-40 Minutes After Heating Up Test Section)... IV- 9
Page
Figure
IV-2E
Temperature Traces from XY Recorder for Run #2
(Subcooled Boiling-Taken on Second Day 20-40
Minutes After Heating Up Test Section)..........IV-10
IV-3A
Pressure Traces from XY Recorder for Run #3
(Bulk Boiling)...............................
IV-13
Pressure Traces from XY Recorder for Run #3
(Bulk Boiling)
.......................
IV-14
IV-3B
IV-3C
Pressure Traces from XY Recorder for Run #3
(Bulk Boiling)................................. IV-15
IV-3D
Pressure Traces from XY Recorder for Run #3
(Bulk Boiling) .................................IV-16
IV-3E
Temperature Traces from XY Recorder for Run
IV-17
#3 (Bulk Boiling) ...............................
IV-4
T1 Temperature Trace from XY Recorder for Run
#4 (Onset of CHF)...............................IV-21
IV-5
T 6 and T 1 Temperature Traces fromXY Recorder
for Run #5 (Step Increase in Heat Flux to
IV-23
Beyond CHF) ....................................
IV-6
T1 Temperature Trace from XY Recorder for Run
#6 (Liedenfrost Temperature) ....................IV-24
V-1
Flow-Pressure Drop Characteristics of Test
Loop with Exit Quality as a Parameter............V - 5
V-2
Flow-Pressure Drop Characteristics of Test
Loop with Heat Flux as a Parameter...............V- 7
V-3
Inlet and Outlet Fluid Temperatures and Tube
Wall Temperature vs. Axial Position for a
Heat Flux of 1.04 x 104 BTU/hr ft2 (Onset of
Subcooled Boiling) ..............................V-10
V-4
Inlet and Outlet Fluid Temperatures and Tube
Wall Temperature vs. Axial Positin for a
Heat Flux of 1.75 x 104 BTU/hr ft (Subcooled
Boiling) .V...................
V-5
V-
Steady State Flow Conditions for Test Loop
V-15
Determined from Figures V-1 and V-2 ..............
Figure
Page
V-6
Comparison of Mass Flow Rates Predicted by
Equation (V-7) with Mass Flow Rate Determined
from Energy Balance (Subcooled Boiling)....... .V-18
V-7
Tube Wall Temperatures vs. Axial Position for
a Heat Flux of 3.83 x 104 BTU/hr ft 2 (Bulk
Boiling) ...................................
V-8
Inlet and Outlet Fluid Temperatures and Tube
Wall Temperatures at T 1, T 2 and T 3 as a
Function of Heat Flux for Run #4 (Onset of
... V-25
CHF) ..
.....................................
V-9
Heat Transfer Coefficient at Location T 1 as
a Function of Heat Flux for Run #4 (Onset of
CHF)......................
...........
....V-27
..
V-10
Flow-Pressure Drop Characteristics of LMFBR
(FTR) with Exit Quality as a Parameter ...... ... V-32
V-ll
Flow-Pressure Drop Characteristics of LMFBR
(FTR) with Heat Flux as a Parameter........
V-12
.V-33
Steady State Flow Conditions for LMFBR (FTR)
V-34
Determined from Figures V-10 and V-ll....... ....
LIST OF TABLES
Table
Title
Page
II-1A
Comparison of Test Section Parameters with
II-16
...............
Current LMFBR Fuel Assemblies ...
II-1B
Comparison of Fluid Conditions for Water Tests
at 14.7 psia with Those for LMFBR at Inception
of Boiling During LOPI Accident ............... .II-17
IV-1
IV - 2
Data for Run #1 (Onset of Subcooled Boiling) ....
IV-2
Data for Run #2 (Subcooled Boiling).............IV - 5
IV-3
Data for Run #3 (Bulk Boiling)......
IV-4
Data for Run #4 (Onset of CHF) ............... .IV-19,
IV-12
............
20
I-1
I.
A.
INTRODUCTION
Background
In the Liquid Metal Cooled Fast Breeder Reactor (LMFBR), coolant
voiding due to boiling causes a positive reactivity feedback and
makes reactor control more difficult.
In addition, post-voiding heat
transfer in the LMFBR is thought to be.ineffective; and it is presently assumed that coolant boiling would result in melting of the
fuel rod cladding.
For these reasons LMFBR's are currently designed
so that the maximum coolant temperature during normal operation is
about 6000 F below the saturation temperature.
Nevertheless, even
with this large margin, reactor safety analyses must consider the
possibility of unanticipated transients or postulated accidents
that would lead to coolant temperature excursions and boiling.
The most serious of the postulated accidents considered is the
Loss of Pipe Integrity (LOPI) accident.
This accident is postulated
to occur as a result of a double-ended guillotine break of a reactor
coolant pipe at the inlet to the core.
Calculations (1) indicate
that, as a result of such a break, reactor flow would decrease to
about 20 to 30 percent of its initial value within 0.5 seconds and
then :remain approximately at this level over the next several seconds.
The pressure in the reactor core is calculated to change
similarly, decreasing from its initial, full flow value to about
25 psia within 0.5 seconds and then remaining approximately constant
at that level.
Since the reactor protection system scrams the con-
trol rods upon sensing the accident condition, the.reactor power
also decreases quickly.
However, because of the stored energy in
the fuel rods and the thermal inertia associated with the properties
and dimensions of the fuel rods, the core heat flux drops more slowly;
I-2
and calculations indicate that it only decreases to about 25 to 50
percent of its initial, full power value during the first 1 - 2
seconds.
Therefore, the sodium coolant in the highest power power
fuel assembly rapidly increases in temperature and is calculated to
begin boiling in about 1 second.
As soon as boiling begins, the
flow is assumed to stagnate,resulting in "dryout" and an increase
in clad temperature to its melting point within about 1 second after
the start of boiling or 2 seconds after the start of the accident.
It should be recognized, however, that the severe temperature
excursion just described is based on present calculational models that
assume flow stagnation and dryout almost simultaneously with boiling.
This assumption results from the fact that analysis and experiments
show that, before boiling begins at the fuel clad surface during a
LOPI accident, the bulk temperature of the sodium would increase to
about 30 to 50°F above the saturation temperature.
Under these
circumstances, once a vapor bubble is formed in the superheated liquid
its growth rate would be very rapid and it would quickly fill the
coolant channel cross section.
This rapid formation of vapor would
be accompanied by a sharp local increase in static pressure that could
stop or even reverse the flow in the upstream section of the coolant
channel.
Although a liquid film would probably initially remain
between the vapor bubble and the wall, the concern is that because of
the flow stagnation, this film would be quickly evaporated, resulting
in overheating of the fuel clad.
The assumption that film dryout occurs as a result of rapid vapor
bubble growth and consequent flow stoppage or reversal when boiling
is initiated during a LOPI accident may be valid.
However, this
assumption has never been put to any real test; and, if it could be
shown that film dryout does not occur immediately after boiling is
I-3
initiated and that substantial heat can be removed under post voiding
conditions, it may be possible to show that clad melting does not
occur.
A possible mechanism for prevention or delay of dryout and
substantial post-voiding heat removal has been suggested by Griffith
(2). This mechanism is described in the following paragraphs from
Reference
(2):
"The cold regions of the core never will boil. As the flow
coasts down, boiling can occur in the hot assembly however,
giving rise to a substantial gravity pressure difference
between the hot and cold channels. This pressure difference
is about 1 ft. of liquid per foot. This pressure head can
be used to overcome the friction and momentum pressure drops
for the evolved vapor in the hot channel. Making the
assumptions of steady-flow, no entrainment, and saturated
vapor out, it is calculated that about 2 kw can be removed in
this way...More, or less, is possible.
A combination of hot rods and two phase flow similar to that
which we have after first voiding in a LMFBR occurs in the
FLECHT-SET experiments (3). In the FLECHT-SET experiments we
find flow oscillations, much carry over, better cooling with
carry over, superheating of the evolved vapor and a host of
other phenomena that are not yet adequately described. It is
not evident which of these will occur in an LMFBR and whether
indeed, they will help or hinder the heat transfer."
The tests described in this report were conceived with the purpose of
obtaining basic information and data relating to this suggestion.
B.
Objective
The objective of the tests was to obtain data and information
concerning the nature and effect of flow oscillations on heat transfer
in a low-pressure natural circulation system similar to the LMFBR under
conditions approximating those predicted to exist during a LOPI
accident at the time boiling begins (about 1 second after the start of
the accident).
It was expected that this data and information would
help to answer some
important questions relating to such conditions
and, therefore, would be of value in designing and interpreting more
I-4
prototypical experiments to be conducted with sodium cooled rod
bundles at the Oak Ridge National Laboratory.
These questions are the
following:
1)
What types of oscillations occur? What appears to be the
cause of these oscillations? How do they affect postvoiding, pre-CHF heat transfer?
2)
Under what conditions does CHF occur? What is the mechanism?
What is the role of the observed oscillations? How is
rewetting and post-CHF heat transfer related to the
oscillations? How does the power corresponding to CHF
compare to the power it takes to completely vaporize a
steady homogeneous flow driven by the hydrostatic pressure
difference between the inlet and outlet of the test section
(or the appropriate length)?
3)
To what extent are the answers to the previous questions
applicable to the LMFBR during the first few seconds of a
LOPI accident?
II-1
II.
A.
APPARATUS
Design Basis
In order to accomplish the objective given in Section I.B, a
test loop was designed to simulate natural circulation boiling in the
LMFBR under conditions approximating those predicted to exist during
a LOPI accident at the time boiling begins.
This design was based
on several simplifying assumptions concerning LMFBR geometry and the
flow conditions that would exist during such an accident.
These
assumptions were the following:
1)
Although, as discussed in Section I.A, there would still
be some pump induced flow through the core when boiling begins,
it was conservatively assumed that this flow is negligible.
Under this condition, the only flow would be due to the
buoyancy force resulting from the density difference between
the boiling sodium in the hot assembly and the liquid
sodium in the colder assemblies. The reactor vessel would
then become a natural circulation "loop" as shown in
Figure II-la. The test loop was therefore designed to
simulate this reactor vessel "loop." This test loop consisted of a vertical tube test section and a down-commer
pipe connected to upper and lower plenum tanks as shown in
Figure II-lb.
2)
As mentioned in Section I.A the sodium coolant pressure is
approximately 25 psia at the time boiling begins and does
not change much over the next several seconds. Because of
the similarity between the liquid and vapor densities of
water at 14.7 psia and sodium at 25 psia (and the expectation that these properties would be of major importance in
determining post voiding hydraulics and heat transfer under
natural circulation conditions), the test loop was therefore
designed to operate with water at a constant pressure of
14.7 psia.
3)
During the first several seconds of a LOPI accident the bulk
liquid sodium temperatures in the upper and lower plenum
would remain at approximately the same temperature as before
the accident. Therefore the test loop was designed so that
the bulk water temperatures in the upper and lower plenum
tanks could be held constant. (The temperatures selected
were such that the negative quality or subcooling in each
plenum tank was the same as for the sodium in each plenum
of the reactor vessel, as will be discussed in Section III.)
4)
Although the heat flux would be changing (decreasing) at
the time boiling begins, the rate of change is sufficiently
small so that the transient natural circulation condition
II-2
a4
U)
O0
Cd a) -Hr:
()
r.
4)
k3:
w
04 W
J4oUJ
0
d
)0
OU
H
0
0
0
14)
r::
k47
a)
4J=HD
H
-,
3a,a
Cd
H
0
.1i
-I
Cd
1-4
0
0
r--
p
zro
u
4J
U)
0
Q)
0
-I-)
4J
04
Hp
H
4i
H
E
)
mO
-H U)OrEn
0r3
U)
3
,x
@
4 W
H
N
TO
a)
(L-N
l-N
0)
P4
En
Q4
0
0
(D
H
03
r-4l-
wO
U,
U)
r-q
P4
1:1
)
a)
04
04
3D
o
0
O O
UW
P;
o
r-
H~
w
m
L
a,
a>)3
f2L
m
C
P47
zb
II-3
at a particular heat flux should be approximately the
same as the corresponding steady state condition at the same
heat flux. Therefore, it was assumed that the test loop
could be operated at constant heat flux using the test
procedure outlined in Section III.B. (However in order to
provide a check on this assumption, a transient test was
run as described in Section III.C.)
5)
The CHF mechanism under LOPI accident conditions would
probably be liquid film "dryout" as discussed in Section I.A.
For this mechanism, CHF generally occurs at the end of the
heated channel or tube and is primarily a function of
channel power rather than local heat flux. Therefore it
was assumed that non-uniform heat flux effects would not be
of major importance, and the vertical tube-test section was
designed to operate with a uniform axial heat flux distribution over its heated length.
As stated in Section I.B, the objective of the tests was to obtain
data and information concerning the nature and effect of pressure and
flow oscillations on CHF and post-CHF heat transfer.
Therefore the
test loop was designed (and operated) to have flow rate - pressure
drop characteristics similar to the LMFBR vessel "loop" shown in
Figure II-la.
The analysis that was done to identify the key geometry
parameters and fluid conditions that need to be matched in order to
obtain this similarity, as well as similarity in other respects, is
described in Section II.B which follows.
B.
Similarity Analysis
Consider the active section of the reactor hot fuel assembly
(Figure II-la) or the heated section of the test loop (Figure II-lb).
Assume that the liquid and vapor are flowing upwards in one-dimensional, homogeneous flow as shown schematically for the heated section
of the test loop in Figure II-2.
For this flow condition, the conser-
vation laws for mass, momentum and energy applied to the control volume
shown in Figure II-2 give the following equations:
For symbols not defined in the text or in Figure II-2, refer to
NOMENCLATURE section at end of report.
II-4
[ PmVm+a (mVm) dz]A
1
1
pm
Vm
Vf+XVfg
Vm
pa
Mass
Fluxes
[ mVmA
A )]d
m(PmVmA)+
[Vm(p
mmVA)+z
mmm
at
[Vm
(mVm
mm~~~
(P+ap
dz) A
3z
dz
-
4
Forces and
1
T rDdz
Momentum
Fluxes
1
m (pMVmA gc
pmg Adz
PM
g
Flow
Direction
I[h(pmVmA)]dz
m
Assume z=O at
the Entrance to
the Test Section
dQ=q" (z) Ddz
h(p VA)
Figure II-2
Control Volume Used for Similarity Analysis
(Section II.A.2)
Enthalpy
Fluxes
II-5
ap
m
t
DP
4-
az
Mg
Pm
D
dQ
=
dQ
=
(II-1)
(PmVm)
-
[
=
m)dz
(uPm)Adz
atM
(P
atmm)
+
+
(PV2)
+ a(pVmmg
]1
(II-2)
a
I[h( mVm )]Adz
az
(II-3)
where
Pm is the density of the liquid-vapor mixture
mA
of the liquid-vapor mixture, W/p~~~~~~~~~~~m
V m is the velocity
m
Equation (II-1) can be combined with Equations (II-2) and (II-3)
to give the following equations for conservation of mass/momentum and
mass/energy:-
Dv
3V
aP
az
_
4D
mm g =
C
at
m av
mVm
]I
9
(ImI-4)
II-6
ah
m at
p
dQ =
zAdz
at + p vm
J ap
(II-5)
Equations (II-4) and (II-5) can also be applied to single phase
liquid flow in other sections of the reactor or test loop providing
that:
Pm is replaced by
L
W
Vm is replaced by VL = pLA
z is defined more generally as the distance along the flow
direction rather than just the vertical distance
Then, Equations (II-4) and (II-5) can be integrated around the loop
to obtain the following integral equations:
_
_
|
.
-L
JD
!dz
INERTIA
(II-6)
_T
_
avVm
-
-
[¢mV
~z
]dz
d(11-7)~~~~~~~~~~~~
h
T
m~~~~~~~~~~~
f
+
z
d
V
P
Q~~~~~~~~~~~
f~~~~~~~~~~~
FRICTION
ACCELERAT ION
GRAVITY
A
P atdz
whereALishelengtho
t L
Qh_z+fu
P0
ah zh or
W asel
(II-7)
0
where L is the length of the reactor fuel assembly or test section in
Figure II-1.
Implicit in these equations are the following assumptions:
II-7
1)
During pressure and flow oscillations, energy storage and
inertia effects external to the reactor fuel assembly or
test section are assumed to be negligible compared to those
within the reactor fuel assembly or test section.
2)
The friction and acceleration effects external to the test
section are negligible compared to those within and entering
or leaving the test section. (The friction and acceleration
effects associated with entering or leaving the fuel assembly
or test section are assumed to be included in the first and
third terms on the right hand side of Equation [II-6]).
3)
The liquid density, PL is approximately equal to the density
of saturated liquid, Pf.
4)
In Equation (II-5) the part of the energy storage term
associated with changes in pressure is assumed to be neglible
compared to the part associated with changes in enthalpy (i.e.,
1[J a]dz
5)
<<
P
m]ah]dz)
The heat capacity of the part of the loop external to the
test section is such that
(Pmah)dz
xternal
=
(PmVm)
dz
m
with essentially no change in the upper and lower plenum
temperatures (as would be the case for the reactor); or
an external heat removal system is provided such that
Qext
=
external 1
)ahmV
l
(Pmm)ldz
Equations (11-6) and (11-7) can be further simplified by using
the following additional approximations and relationships:
II-8
I
p
avm
()d__
z
( at dm
=
raw
dt
L
Agc
D dz
dL 2_
__w
PfL +PmL2
R
[f
(Pf m)dt
dt
c
Ll]2f
2
2-
0
2
)
2 PfA
1
L
J
f
Pm
1$
dz = (Pm-Pf)q
f)g
(P-
I
_ =1
1
L2~
L 2~
L2
d
f
1
Of
f"
L
P
ad
Pm ah
= hfgp gL
+s
(Pf-
dt
?T
d
L
f0
mm
z
A
fg(Xout-X 1 )
where
L¢ is the length of the single phase liquid region within
the reactor fuel assembly or test section.
L1l is the equivalent length of the single phase region,
including the effect of inlet contraction and orifice.
L2% is the length of the two phase region within the reactor
fuel assembly or test section.
L2~ is the equivalent length of the two phase region,
including the effect of outlet expansion.
f is the Fanning friction factor.
II-9
xout-xl.is the quality change along the test section, where
x 1 is equal to Cf(TlTsat) and T 1 is the inlet plenum
ha
-'a
temperature.
*
Thus
J
L
+
PfLl +mL
dt
Ksc
dL
W
.
%
2
=- (P
-- L
(fPM
20
- 14f(2p
-
f M dm
t
Q = hfg pgA
P L
-dt
- 22 dtI
i
D.
+ R
L
2
(II-8)
W2
15
d20
d
dL
and
d
dm
+
+L2
dt ]
L2
+ Whfg(Xout-
1)
(II-9)
L
Now, for steady flow,
d
and (II-9) are equal to zero
0 = (f-Pm)
terms in Equations (II-8)
and these equations become:
-
L2
9c2
ad -
[4f(
Ll+L
D D2)1
D
W2
2pfA29
(II-10)
and
(II-11)
Q = Whfg(xout-xl)
Also, L,
L1i'
L 2 , and L 24 can be expressed in terms of L1 , L 1 (the
equivalent length of the unheated inlet section), L , L (the equivalent
2
2
length of the unheated outlet section).,
LH (the heated length) and
LB (a "boiling" length) for the test section or reactor assembly by
the expressions:**
L1l = L 1 + (LH - L B)
.
1
L1
= L i + (LH -L
L2
= LB + L 2
= L
L
L2 =
B)
(II-12)
+ L
i
A,
*Note that Xou t /
temperature.
**See Figure
II-3.
2
= Cf(T2-Tsat) where T 2 is the upper plenum
hfg
II-10
Figure II-3
Schematic Diagram Relating L
to L 1 , L2 , L H and L B
H
~B
and L
II-11
where LB is defined in terms of mass flow rate, inlet quality, power,
heat flux distribution and LH by:
L 1+L H -LB
-Wxl
q"(z)dz
1
_
________
______
L1+LH
(11-13
)
Q/hfg
q"'(z)dz
1
which, for a uniform heat flux distribution would become:
LH-LB
LH
=
-Wx1
1
(Q/hfg)
(II-14)
Therefore, for steady flow conditions and uniform heat flux distribution, one can conclude from Equations II-10, II-11, II-12 and II-14
that:
W =
(pfpgxlh,
Q
f or
f and wall
fglfQ
roughness,
(II-15)
L 1 ,L1 ,LH,L2 ,L2 ,A,D)
or
xout = Xout (same parameters as for W)
(11-16)
This means that, for steady flow conditions and neglecting effects of
non-uniform axial heat flux distribution, W and xout will be the same
for the test loop and the reactor providing the following parameters
are the same for the two systems:
Pf' Pg
(T-Tsat)
or C
x
x1
f
hfg
_Q
hfg
pf and wall roughness
!
I
'L1,LHL2 L2
A
D
II-12
For unsteady flow conditions, such as would result from oscillations between two possible steady flow conditions, the above result
(along with consideration of Equations [II-8] and [II-9])
dL2 ' and dtm (and therefore Wt]
that dW
dt
and x
indicates
[t]) would also be
the same for the test loop and the reactor if the above parameters are
the same.
However, Equations (II-8) and (II-9) were derived for up-
flow; and, since flow oscillations might cause momentary downflow of
liquid from the upper plenum, the following additional parameter
should probably also be included if W(t) and x ou(t)
are to be the
same for the two systems:
X2 or Cf(T2-Tsat)
hfg
For both the test loop and the reactor, it is expected (as discussed
previously in Section II.A) that CHF would be due to "dryout" of the
liquid film under annular flow conditions.
Under such conditions, CHF
would occur at the top of the heated length when (Q/hfg) is sufficiently
high so that the exit quality exceeds some critical value.
If one
assumes that any liquid present at the CHF location would wet the
heated surface, this critical quality would be 1.0; and the critical
value of Q/hfg corresponding to CHF could be determined from Equation
(II-16) by setting xout
out = 1.0.
1.0.
Moreover, this critical hfg
hQ would be
the same for the reactor and the test loop providing the parameters
listed previously are the same for the two systems.
However, it is probable that some of the liquid at the CHF location
would be entrained by the vapor and would not be able to wet the heated
surface.
In this event, the quality at the CHF location would be less
than 1.0 and the critical (Q/hfg) would also be a function of any
parameters that would affect the amount of liquid entrainment.
Such
parameters would include the liquid surface tension in addition to the
II-13
parameters listed previously.
Therefore, the liquid surface tension
should be the same for the reactor and the test loop if the critical
(Q/hfg) is to be the same.
(Of course, this condition could not be
even approximately satisfied, since water was the fluid used for the
test loop and the surface tension for water is substantially less
than for sodium.
Nevertheless, because of this difference, sodium
would be expected to have less entrainment for an otherwise identical
flow condition.
Therefore, the water tests should indicate a conser-
vatively low exit quality or [Q/hfg] at CHF.)
If the flow is oscillating when CHF occurs, the liquid film flow
rate at the CHF location would also oscillate and could be very small or
essentially zero for short periods of time.
Under such conditions,
the critical (Q/hfg) would probably be influenced by the conductivity
of the liquid film,in addition to the previous listed parameters.
(As for the surface tension, it was not possible to satisfy this
condition,since the conductivity of water is much less than for sodium.
However, this is again conservative in that a lower liquid conductivity
should result in a lower critical value of Q/hfg.)
Post CHF hydrodynamics and heat transfer would be a function of
parameters that influence the Liedenfrost temperature.
But, such
parameters would include only the liquid surface tension and those
parameters previously listed as determining the mass flow rate and
exit quality.
The surface tension (along with the surface material
and roughness) would determine the contact angle and therefore the
wetting characteristics of the fluid-surface combination.
(See
parenthetical comment regarding surface tension in previous paragraph.)
For post CHF conditions where the heated surface oscillates as
a result of periodic dryout followed by rewetting, the initial rate
II-14
of temperature rise subsequent to dryout (and therefore the time
available for rewetting before the Liedenfrost temperature is exceeded)
would depend upon geometry and thermal properties of the tube wall or
clad.
This is shown by the following approximate equation derived from
an energy balance on a differential length of the tube wall or clad,
assuming negligible heat transfer to the coolant:
dT
_= =
dt
PsCs6
(II-17)
where ps, Cs and 6 are, respectively, the density, specific heat and
dT
thickness of the tube wall or cladding. Therefore, if dtS is to be
the same for the test loop and the reactor for a given post CHF q",
Ps, Cs and 6 for the tube wall and clad would have to be the same; and
these parameters should also be added to those listed previously.
(Since stainless steel was used for the test section and is also the
reactor clad material, ps and C s were about the same.
However, it was
not possible to match 6; and therefore 6 for the test section tube was
about a factor of three greater than for the reactor clad. Also,
because of the difference in hfg between water and sodium, the value
of q" corresponding to a given post CHF value of (Q/hfg) would be lower
for the test loop than for the reactor by about a factor of 2. TheredT
fore
-:for the test loop under post CHF conditions was about a factor
of 6 lower than would be expected for the reactor for the same (Q/hfg).
This, of course, is not in the conservative direction; since the lower
dT
t +would allow more time to rewet the
heated surface before the
Liedenfrost temperature is exceeded.
C.
Description of Test Loop
1.
General
A schematic diagram of the test loop is shown in Figure II-4.
Tables II-1A and II-1B compare values of the parameters identified from
II-15
vent
Upper Plenum Tank
Drain
_
.L=
:er
)r
:ical Tube
: Section
.152 in.
sducer
* Section
in.
Insulate
Flanges
Electrical
Leads
I
I1
ection
I
icator
t
oled
Flexible
Section
er
Lower Plenum Tank
Figure II-4
Schematic of Water Test Apparatus
II-16
Table II-A
Comparison of Test Section Parameters
with Current LMFBR Fuel Assemblies
Parameter
Test Apparatus
FTR
CRBR
Heated Surface
Material & Geometry
Electrically
Heated Tube
316 ss Clad
Fuel Rod Bundle
316 ss Clad
Fuel Rod Bundle
7
7 in.
14 in.
in.
10.5 in.**
131 in.***
36 in.
36 in.
36 in.
48 in.
48 in.
62 in.
55 in.**
57 in.***
0.152 in.
0.128 in.*** for
average subchannel
91 in.
91 in.
0.0181 in2
0.0154 in. 2*** for
average subchannel
Surface Roughness
Commercial Tubing
Approximately Same as Commercial Tubing
P
494 lbm/ft
LH
3
m
112 in.
498 lbm/ft3
m
498 lb ft3
m
0.12 BTU/lbmOF
0.12 BTU/lb
0.049 in.
0.015 in.
°F
0.12 BTU/lbmOF
0.015 in.
*See Figure II-1 and NOMENCLATURE for definition of symbols
**See discussion in Section II.C.2
***See discussion in Section V.B.1
II-17
Table II-1B
Comparison of Fluid Conditions for Water Tests
at 14.7 psia with Those for LMFBR at Inception
of Boiling During LOPI Accident*
Fluid
Condition**
Water
Tests
FTR
CRBR
P
14.7 psia
25 psia
25 psia
212°F
1670°F
0 F
1670
Pf
59.8 lbm/ft3
46.4 lbm/ft3
46.4 lb /ft 3
Pg
0.0373 lbm/ft3
0.025 lbm/ft3
0.025 lb /ft3
(Pf/P g)
1603
1865
1865
hfg
970.3 BTU/lbm
1650 BTU/lbm
1650 BTU/lbm.
Cf
1.0 BTU/lbmOF
0.31 BTU/lbm ° F
0.31 BTU/lbm ° F
T1
70OF
792°F
725°F
-0.146
-0.165
-0.173
110°F
1100OF
995°F
-0.105
-0.107
-0.126
If
0.687 lbm/ft hr
0.363 lbm/ft hr
0.363 lbm/ft hr
df
0.004 lbf/ft
Approximately
0.012 lbf/ft
Approximately
0.012 lbf/ft
kf
0.394 BTU/hr ft°F
31.5 BTU/hr ftF
31.5 BTU/hr ft°F
sat
sat
x1 or
Cf(T 1 -Tsat )
hfg
T2
Cfor
f(T T sat)
2 Or
m
hfg
*In accordance with assumptions outlined in Section II.A.1
**See NOMENCLATURE for definition of symbols
II-18
the similarity analysis in Section II.A.2 with corresponding values of
these parameters for current LMFBR designs (FTR, CRBR).
The principal components of the test loop included:
(1) a verti-
cal tube test section, (2) two sight flow indicators, (3) upper and
lower plenum tanks, (4) an external down-commer, (5) a power supply
A description of each of these components
and (6) instrumentation.
is given in the subsections that follow.
2.
Test Section
The vertical tube test section was made from commercial, Type 304
stainless steel tubing with an inside diameter of 0.152 in. and a wall
thickness of 0.049 in.
It consisted of three sections:
(a) an unheated
inlet section that was 7 in. long, (b) a heated section that was 36 in.
long, and (c) an unheated outlet section that was 48 in. long.
The
total length was therefore 91 in.
The equivalent length of the unheated inlet section (including the
effect of the inlet contraction) was 10.5 in.
The equivalent length
of the unheated outlet section (including the effect of the outlet
expansion) was 54 in.
(See Table II-1A.)
These equivalent lengths
were obtained from the following equations:
,K1D
L1
7 +
1
and
L
(II-18)
KD4f
= 48 +
(II-19)
2
4f
where K1 , K2 and f were assumed to have values appropriate to single
phase flow regardless of the flow condition.
These values (based on
information from Reference (4) were the following:
K1
= 0.5
K2 = 1.0
f
= 0.0055
II-19
The test section was connected at each end to a sight flow
indicator by means of a Swagelok fitting.
The sight flow indicators
were in turn connected to the upper and lower plenum tanks by means
of a bushing and a coupling welded to the tank covers.
fittings were stainless steel.
All of these
The test section, sight flow indicators
and plenum tanks were supported by a Dexion frame, bolted to the floor
and ceiling of the laboratory room.
The test section was vertically
aligned by means of adjustable clamps made of aluminum.
3.
Sight Flow Indicators
The sight flow indicators also were obtained from a commercial
supplier (Ernst Model No. EEP 4000-S).
Each of these indicators
consisted basically of a glass tube with an inside diameter of 7/8 in.
and a length of 4 7/8 in.
The glass tube was partially enclosed within
a bronze support structure with 1/4 pipe fittings at each end.
See
Figure III-5.
4.
Plenum Tanks
The upper and lower plenum tanks were made from 8 in. stainless
steel pipe and 1/4 in. stainless steel plates as shown in Figure III-6.
Stainless steel couplings were welded to each tank to make connections
to the test section and external down commer as indicated.
The upper plenum tank was provided with additional couplings
and fittings for:
(a) avent to the atmosphere, (b) hot and/or cold
tap water to flow through a coil of copper tubing located inside, (c)
a sight glass to allow viewing of the water level, and (d) a thermocouple well.
fittings for:
The lower plenum tank was provided with additional.
(a) allowing direct flow of cooling water to and from
an external pump and heat exchanger and
(b) a thermocouple well.
II-20
H1
0-
1/2 inky
! K
r
Glass Tube
5/8 in. ID
.Ar,
.,
Nr
Bronze
Housing
·
JA
_
_1
LX
F
1/4 in. Pipe Size
Figure II-5
Sight Flow Indicator
II-21
n. Stainless Steel
Plate
Hot or Cold Tap Water
(
:8 in. ID Stainless
Steel Pipe
ro Drain
To
- Flow Indicator
Thermocouple Well
a) Upper Plenum Tank
To Bottom Sight Flow Indicator
Thermocouple Wel 1
1/4 in. Stainless Steel Plate
\X
m
'1/
l
ALArrtnl
.,
0.
ro
I
.
U.
8 in. ID
prnm Ryt-rnal
I
Stainless Steel--Pipe
8
'Heat Exchanger
.n.
I
I"_a_
From Down-Commer
xternal
Heat Exchanger
To
w
"
[1
b) Lower Plenum Tank
Figure II-6
Upper and Lower Plenum Tanks
II-22
A schematic diagram is shown in Figure II -7 of the hydraulic
system and heat exchanger
used to control the fluid temperatures in
each of the plenum tanks.
The heat exchanger for the upper plenum was
located within the tank and consisted of two 6 ft. long coils of
3/8 in. O.D. copper tubing.
Hot and/or cold tap water was circulated
through the coils to a drain.
The heat exchanger for the lower plenum
was a couterflow, shell and tube heat exchanger and was located
external to the tank.
Cold tap water was supplied to the shell and
water from the lower plenum tank was circulated through the heat
exchanger tubes by means of a small centrifugal pump.
Flow rates
were controlled with globe valves located as shown in Figure II-6.
The heat exchangers and all piping and valves were made of copper and
bronze.
5.
Down-commer
The down-commer was made from 1 in. I.D. stainless steel pipe
and fittings except for the flexible section included to allow for
thermal expansion of the test section.
from
in. I.D. braided brass pipe.
The flexible section was made
The 1 in. pipe size was chosen
on the basis that it was sufficiently large compared to the test
section diameter of 0.152 in. so that down-commer hydraulics had
essentially no effect on the loop flow-pressure drop characteristics.
6.
Power Supply
Power to the test section was supplied by a 15 kw DC generator,
rated at 15 volts and 1000 amperes.
220 volt, 3 phase AC motor.
The generator was driven by a
A portable control console was provided
to regulate the generator power from zero to the maximum as required.
This regulation was accomplished by a set of coarse and fine rheostats.
A knife switch located on the portable console could be used to quickly
II-23
Copper Tube Coil
e~
upper
Plenum Tank
Drain
To
Down-Commer
From Test Section
Copper Pipe
Cold
.
To Test Section
i-II
Bronze Globe Valves
/
From
Down-Commer
Lower Plenum
Tank
Circulating
Pump
_
Figure II-7
Schematic of Hydraulic System and Heat
Exchangers Used to Control Upper and Lower
Plenum Temperatures
_
_
_
-
_
II-24
stop (or start) the flow of current from the generator without stopping
it or changing the rheostat settings.
Current from the generator was supplied to the test section
through four flexible neoprene welding cables connected to each end
of the heated section.
The cables were clamped to an aluminum lug
which was in turn clamped to the test section, as shown in Figure
II-8.
The heated section of the test section was electrically insulated
from the rest of the loop by two flanges located about 3 in. upstream
and downstream of the heated section.
The flanges were designed in a
way such that the continuity of stainless steel along the test
section was interrupted by a small teflon insert that, in effect,
replaced the tube wall at the location of the flange.
The design of the
flange was such that the effect on flow through the test section would
be negligible.
7.
Instrumentation
Instrumentation was provided to measure loop temperatures and
pressures and power to the heated section of the test section.
A
schematic diagram is shown in Figure II-9.
Temperatures were measured by thermocouples located to provide
measurements at 15 locations.
Thermocouples T 1 through T10 were
located at 10 positions along the outside wall of the heated section
as shown in Figure II-10. Tll was located on the outside wall of the
unheated inlet section.
T 1 2 was inside the thermocouple well located
in the top cover plate of the lower plenum tank.
T 1 3 was located
on the outside wall of the unheated outlet section.
T 1 4 was inside
a thermocouple well located in the lower cover plate of the upper
plenum tank.
II-25
Stainless Steel
Tube
Tap for Voltage
Measurement
r
Welding Cable
I
Aluminum Power Lug
II-__
Pressure Tap
II
-
ed to SS Tube
-
.Stainless Steel
'op Part of Flange
II
I:
i:
IJ
sulator
thick
Silver So
to SS
3teel Spacer
Stainless Steel
ower Part of Flange
in Contact with Tube)
Insulated Flange
Figure II-8
Detail of Test Section Showing Power Lug
Connection and InsulatedFlange
II-26
TC15
TC15
TC14
Millivoltmeter
TC13
,uble Pole
Switch
V
TC
PT1
.
.
uble Pole
Switch
3 Position
L.
j
.,.:
,w-tcn
Figure II-9
Schematic of Loop Instrumentation
II-27
T14
13
3 7/8
----
in.
-
-
6
in
.
5 Ir
I
36 in.
1/-4in. from End of Heated Length)
3 in.
6 in.
6 in
-
6 in.
6 in
6 in.
9 in
6 in.
6 in
__J6
Start of
Heated
Length
2 5/8
in.
t
T12
16 3/8 in.
-Pi
Figure II-10
Location of Pressure and Temperature
Measurements
II-28
All thermocouples were made of 30 ga. chromel-alumel thermocouple
The thermocouples attached to the test section were electrically
wire.
insulated by a 0.002 to .003 in. thick layer of mica.
They were held
against the tape by means of asbestos string wrapped several times
around the thermocouple and mica.
Thermocouple output could be measured by either a potentiometer
or an XY recorder.
This was made possible by connecting each of the
15 thermocouples to a 16 position switch which was in turn connected
to a double pole switch connected to the potentiometer and recorder.
See Figure II-9.
Pressures were measured by three Tyco Type AB pressure transducers
with a range of 0 - 6 psig.
batteries.
Excitation was provided by 6 volt dry cell
The calibrated full scale output of each transducer at
6 volts excitation was 120 mv + 1%.
P1 was mounted in the wall of the lower plenum
shown in Figure II-9.
tank.
The transducers were located as
P 3 was mounted in the lower half of the insulating flange below
the heated section.
P3 was mounted in the upper half of the insulating
flange above the heated section.
As for the thermocouples, the output of the pressure transducers
could be measured by either a potentiometer or an XY recorder.
This
was accomplished by connecting each transducer to a three position
switch which was in turn connected to the potentiometer and recorder.
See Figure II-9.
Power to the test section was obtained by measuring the current and
voltage drop.
The current was determined by measuring the voltage drop
across a standard shunt using a Model 322 No. 396 millivoltmeter with a
0- 18 mv
50 mv
range.
The shunt was calibrated to give a voltage drop of
at 1000 amperes.
The voltage across the test section was measured
II-29
directly with a Triplett Model 4235-F multirange digital voltmeter.
The voltage taps were clamped between the test section wall and the
aluminum power lug shown previously in Figure II-8.
III-1
III.
A.
TEST PROCEDURES
General
The test procedures were designed to simulate heat transfer and
flow conditions approximating those predicted to occur at various
times during the first few seconds of a LMFBR LOPI accident.
The
choice of these procedures was based on consideration of the LOPI
accident sequence described in Section I.A.and the assumptions outlined
in Section II.A.
Three types of tests were conducted.
The first was a steady state
test in which the test section power was.slowly increased to the desired
test condition and then held constant while data was taken.
The second
was a transient test in which the test section power was increased
almost instantaneously to the level corresponding to the desired
condition.
The third was a transient cooling test to determine the
Liedenfrost temperature.
The detailed procedures used for each of
these tests are outlined in the subsections that follow.
B.
Steady State Tests
During a LOPt accident, the coolant in the hot fuel assembly goes
through a succession of flow conditions ranging from forced convection
of subcooled liquid to natural convection flow boiling and CHF.
The
procedure used for the steady state tests was designed to produce this
same sequence of conditions, except that for each condition the only
flow was due to natural circulation.
1)
The procedure was the following:
The water temperatures in the upper and lower plenum tanks
were adjusted by controlling the flow of hot and/or cold tap
water to the heat exchangers described in Section II.C.3.
The upper plenum temperature was adjusted to 1100 F. The
lower plenum temperature was adjusted as nearly as possible
to 700 F. These temperatures were selected to produce upper
and lower plenum qualities approximately equivalent to those.
that would be expected in the FTR during the first few seconds
of a LOPI accident (see Table II-1A).
III-2
2)
The power to the test section was then slowly increased
until the heat flux was at the desired level; and the water
flows to the upper and lower plenum heat exchangers were
adjusted as required to maintain the temperatures set in Step 1.
3)
Once the desired flow condition was established, data was
recorded and conditions observed at the sight flow indicators.
Data taken included: (a) test section power (voltage and current)
and (b) test section and plenum temperatures and pressures
(potentiometer readings and XY recorder traces). Observation
of conditions at the sight flow indicators were made with the
following questions in mind: What is the flow regime entering
or leaving each end of the test section? If the regime is
two-phase, what is the spatial configuration of vapor and
liquid? Is the observed flow regime steady? If not, what is
the nature of the observed oscillations? How do these oscillations appear to correlate with data taken with the XY
recorder?
4)
During a particular run, while data was being taken as
described in Step 3, the upper and lower plenum tank temperatures were periodically checked and adjustments were made to
the water flows to the upper and lower plenum heat exchangers
as necessary to maintain the conditions initially established
in Step 1. (For some of the runs, problems with the pump used
to circulate water to the lower plenum heat exchanger made
this step difficult, as noted in Tables IV-1, IV-2, and IV-3
of Section IV.A.)
5)
Three test runs were conducted as outlined in Steps 1 through
4. The first was at a heat flux of 1 x 104 BTU/hr ft2
(approximately the onset of subcooled boiling). The second
was at a heat flux of 1.75 x 104 BTU/hr ft2 (subcooled boiling).
The third was at a heat flux of 3.83 x 104 BTU/hr ft2 (bulk
boiling). The fourth was at a sequence of heat fluxes ranging
from 1.3 x 104 to 7.3 x 104 BTU/hr
C.
ft2
(beyond CHF).
Transient Tests
After completion of the steady state tests, two transient tests
were conducted using the following procedures:
1)
After the steady state test at 7.3 x 104 BTU/hr ft2 (beyond
CHF) was completed, the power to the test section was
decreased to zero by opening a knife switch in the power
supply circuit. Then, after waiting for the test section
temperatures to decrease to their equilibrium, zero heat
flux levels, the test section heat flux was increased almost
instantaneously to its initial value by closing the knife
switch. During the initial part of the resulting transient
the test section wall temperature at location T6 (near the
center of the heated length) was followed using the XY
recorder. Later in the transient the temperature at location
III-3
T 1 (near the top of the heated length) was followed.
Observations of the conditions at the sight flow indicators
were also made during the transient to see how fast the
original flow condition appeared to be reestablished.
3)
Next, a transient cooling test was run to determine the
Liedenfrost temperature. This test was initiated from a zero
heat flux condition. First the test section power was slowly
but steadily increased until the heat flux was about 8 x 1-04
BTU/hr ft2 . The tube wall temperature at the top of the
heated section was allowed to increase to a temperature beyond
1500F (well above the Liedenfrost temperature expected on the
basis of previous steady state tests beyond CHF). When the
temperature had exceeded 15000 F the power was quickly
decreased to well below the power required for CHF. During
the resulting transient, the temperature at location T1 was
followed using the XY recorder in order to determine the
tube wall temperature at which the cooldown rate increased
significantly (Liedenfrost temperature).
D.
Data Reduction
1.
Thermocouple Data
The thermocouple data was obtained as mv readings from the
potentiometer and the XY recorder traces.
The Y scale on the
recorder traces was converted to mv by setting the pen at zero for
the zero mv condition and then using the Y scale setting (mv/division).
This conversion was periodically cross checked by comparison with the
potentiometer reading of the same thermocouple.
The fluid temperatures were relatively steady at Locations Tll,
T13 (inlet and exit of the heated section) and T 1 2 , T 1 4 , T 1 5 (plenum
tanks).
Therefore the mv readings corresponding to these temperatures
were obtained from the potentiometer readings. On the other hand,
temperatures at Locations T1 through T 1 0 (along the outside wall of
the heated section) were observed to change with time as a result of
oscillations of the test section pressure and flow.
Therefore, mv
readings corresponding to temperatures at these locations were
obtained from the XY recorder traces by estimating the average reading·
over several minutes.
III-4
Millivolt readings obtained from the potentiometer and/or recorder
were converted to
F by means of standard calibration tables for
chromel-alumel thermocouples.
The fluid temperatures obtained from
this conversion are the values listed in the data tables given in
Section IV.
The test section outside wall temperatures along the
heated length (obtained from conversion of the average readings
estimated from the XY recorder traces)were, however, first corrected
for the temperature drop across the tube wall.
This was done using
the following equation from Reference (12):
2k
R2
2R2
q"R
T.1i = T o +
(1
2
2
R-R
2 1
nn
)
(III-1)
1
where
T i, To are the inside and outside tube wall temperatures
R1 , R2 are the inside and outside tube radii
k is the thermal conductivity for stainless steel
110 BTU/hr
150 BTU/hr
ft
ft
F at 212°F
F at 950 ° F
q" is the inside surface heat flux
The resulting inside tube wall temperatures are the values listed
for locations T 1 through T1 0 in the data tables given in Section IV.
Errors in the temperature data would be due to thermocouple and
and measurement error.
This error should be within + 1F
for those
temperatures which were not oscillating and were obtained directly
from the potentiometer readings.
On the other hand, for those
temperatures that were oscillating and therefore were averaged, the
error could be as much as + 5F.
2.
Pressure Transducer Data
The pressure transducer data was obtained as my
readings from
the potentiometer and XY recorder traces in the same manner as described
III-5
for the thermocouples.
However, because of the large pressure oscil-
lations observed for most of the test conditions, the potentiometer
was only useful as a check on the recorder Y scale conversion
(mv/division).
Millvolt readings from the XY recorder (or the potentiometer when
such readings could be made) were converted to psig. using the following equation.based on information provided by the manufacturer:
reading x 0.3
P(psig) = mv.
excitation
voltage
(III-2)
(The excitation voltage provided by the dry cell batteries was measured
before each run by the digital voltmeter described in Section I.I.C.7.)
According to the manufacturer, the.full scale accuracy of the
transducers used for the pressure measurements was + 1 percent of the
full scale reading of 6 psig.
This was checked by comparing measured
and calculated static pressures at zero power and found to be a little
low.
Differences of up to + 3 percent were observed in these
comparisons.
3.
Test Section Power Measurement
Test section power was obtained from the measurements of test
section current and voltage using the following equation:
mv
(volts) ('
Q(kw)
=
x 1000)
0
1000
(III-3)
where (m x 1000) is the test section current in amperes based on the
millivoltmeter readings and the shunt calibration.
The test section heat flux was obtained from the power measurement
by means of the equation:
q,, = Q(3413)
nDLH
III-6
or
q"(BTU/hr
ft2 ) = Q(kw)(2.859
x 10 4)
(III-4)
Errors in the power measurement and therefore in the heat flux
would be due to instrument error and unsteadiness during a test run.
Error in the heat flux would also be due to heat loss to the atmosphere.
(For the initial runs at lower heat flux [Runs 1, 2 and 3]
the test section was not insulated.
But, for the later runs up to
and beyond CHF, about 1/4 in. of asbestos tape was wrapped around the
heated section.)
Considering both sources of error, the error in the
calculated heat flux values is estimated to be less than + 5 percent.
4.
Calculation of Flow from Energy Balance
For those test conditions for which the test section exit fluid
temperature was less than the saturation temperature , the average
flow through the test section was obtained from an energy balance on
the heated section.
The equation used was the following:
W(lb/sec)
=
Q(kw) (3413)
Cf(T 1 3 -T 12 ) (3600)
5.
(III-5)
Calculation of Heat Transfer Coefficients
The heat tranfer coefficient at the top of the heated section
was calculated using an average of the inside tube wall temperatures
at Locations T1 and T 2.
The equation used was the following:
'1,2
T +T
2
The values of W and h2
Section IV.
(III-6)
13
are also included in the data tables given in
IV-1
IV.
DATA AND OBSERVATIONS
A.
Steady State Tests
1.
Onset of Subcooled Boiling (Run #1)
Steam bubbles resulting from subcooled boiling were first
observed at the top sight flow indicator when the heat flux was about
1 x 10
4
2
BTU/hr ft
.
Data for this test condition are given in Table
IV-1 and Figures IV-lA and IV-lB.
The corresponding observations at
the sight flow indicators were the following:
Top. Conditions changed periodically. Small bubbles were
observed continuously at the top sight flow indicator. Periodically, the flow would appear to slow down momentarily followed
by the appearance of much larger bubbles over the next several
seconds.
Bottom.
2.
Only liquid was observed.
Subcooled Boiling (Run #21
Subcooled boiling was the heat transfer mechanism at the top of
the heated section for heat fluxes between 1 x 104 and 3 x 104
BTU/hr ft2 .
As the heat flux was increased within this range the
following observations were made at the sight flow indicators:
Top. Conditions continued to change periodically as observed
for Run #1. However, the frequency of these changes increased
as the heat flux was increased.
Bottom. Single phase liquid flow continued to be observed until
onset of saturated boiling at about 3 x 104 BTU/hr ft2 . At this
heat flux, a spurt of small steam bubbles was observed every
few seconds at the lower sight glass. However, these bubbles
condensed within the first inch or two below the top of the glass.
Data corresponding to a heat flux of 1.75 x 104 BTU/hr ft2 are
given in Table IV-2 and Figures IV-2A, IV-2B, IV-2C, IV-2D, and IV-2E.
The data in Table IV-2 are an average of results obtained on two
successive days.
Figures IV-2A and IV-2B show the pressure and
temperature traces taken on the first day, immediately after completion
of Run #1.
Figure IV-2C shows pressure and temperature traces taken
IV-2
Table IV-1
Data for Run #1 (Onset of Subcooled Boiling)
Power
0.363 kw
Heat Flux
Average
ft2
1.04 x 104 BTU/hr
Flow
3.74 x 10
3
lb /sec.
Heat Transfer
2
325 BTU/hr
at 1,2
Coefficient
Average Tube Wall
Temperatures
Location
T1
(psig)
Without
Heat
With
Heat
P1
4.01
3.92
P2
3.66
3.65
P3
2.30
2.21
I
210
I
T4
T5
°F
I
T2
T3
Average Pressures
°F
206
ft
I
i
189
T6
T7
176
T8
T9
169
T 10
147
I
I
NOTES
T 11
78-85
T12
77-85
1)
T1 3
174
2)
T14
109
T1 5
107
See Figure
II-9 for locations
of
pressure and temperature measurements (T1 , P1 ...etc.).
Circulating pump for lower plenum
cooling was overheating. Therefore,
it was necessary to turn it off
during the run and Tll drifted from
78.5 to 850 F while other data was
being taken.
s ec. -
-1
-
w
, AI
---- +-4------
,
.
.:
_
:
i-! .-._ ....-
:
'r
I L
___
_i
I.
IV-3
-
-
___.__ . _I
-
-
_ _ __
i
.
..____.
4_ __
!:_t
I
I
:
I
:
____.-
_-
I
. ___-
- I1-------
--
. I
I
.--- - -
4a
eU
A:-
--
I
I - -
P3
.
w
_ .
--- ..
_
.
--
v
Elr
a-fty..
at ft
, -&W"2
l
A
--
:-
I ___EP040044
L._
I-
--
_.
..
.
.
.
--
F'
.
i
_-
...1-'-
-
.
I.
t-i L
I
I.
-;
i
I
jI
4
..
_
_
__
_
- -
!
.-
.~
k
.
_
E-
r
-e
---
-
,.
.
I
.I
_
- _
-
.
i·
.
____-
.
L
I
-
I,- --:-
i'.-'
-
. ..
_-·
I
'
.
_
IA
_ _
_ _
-
.
.-
-
A
n
_i
41>1.- :4i.!·
. L.
.I
.- . A.. .
.
.
. .....
.
A
4
-.
f-I
____
I
I
|
I
'-
*-VH
i ?!.
;
I
-.-
: __~~t - _:;._. . I i
:F.[17t7I7
-
-- -'-'
..
-
*
,
f
.
-
·t
1
'
,
|
I _.
I
.-
-
__
,_
f
-
.
,-
,
I
..
i
f.,
. I - . .
- -T
-1.
_.
I
--------
. ._
· ;·C·:C·'
' 4t
:=4·
I- _-
_~
_
1-
- ..1 .
-_
4
- !
T---
10 ml
or
.51
4.7§
|
i,
.4.2.....
.
·r~-lk~lCII-·--~ -·IIC~! C~.~l C·
..,,I
to4
.
:
i
1.
._O.'.-.
_.. .
'-.
--
i-- ! -Ir-'I
I.I
-
..
_
._
4
IRT
'
1
.. ..
, ,.
. I
...- -:'-:
_-_:VV
P1
-- -.
·
.
p2
'
_
_
.
I- . I . ._
I-I
.
'
I
'
. I
...
,
_
-- I
.
-
.
L
--
~- .!
'. ]
- ---t .
--
!
L_
II__
_... :.-
. -- 'TL ---..
.
I '
-.i
_
I
...-T
_
__
I--'''------4
1
.1 I
:
.
-1-t
- -- I
i
.........
Note: These traces were taken
sequentially and not simultaneously.
Figure IV-lA
Pressure Traces from XY Recorder for Run #1
(Onset of Subcooled Boiling)
IsJ-g
IV-4
0 4.
FL
*0
C,-)
m
o
I -r-
N
I
-
-
nU)
3
OO
U)r
a)z
0
44
O
-,z
o
m
rH
U)
O
WO
Q
044 E
1
.--I il
4
U 4-4
:4
WO
#0
I
E Q,4
4m
H
EH
j
1.i
Eq
U1
EH
rH-4
r-I
H-
IV-5
Table IV-2
Data for Run #2 (Subcooled Boiling)
Power
0.606 kw
Heat Flux
Average Flow
4.73 x 103
Heat Transfer
Coefficient at 1,2
T1
lbm/sec.
865 BTU/hr ft2 OF
Average Tube Wall
Temperatures
Location
ft2
1.73 x 104 BTU/hr
Average Pressures (psig)
0
OF
Location
Without
Heat
Heat
With
Heat
P1
4.01
3.88
P2
3.66
3.41
P3
2.30
2.18
215.5
T2
218.5
T3
T4
T5
T6
189.5
T7
183
NOTES
T8
T9
L
1)
See Figure II-9 for locations of
pressure and temperature measurements (T1 , Pl...etc.).
2)
Instead of leaving circulating
pump off as was done for Run #1,
it was turned off and on periodically. In this manner it was
possible to maintain T 1 1 and T 1 4
constant to within about + 2 0 F.
Start and stopping the circulating
pump and varying the flow to the
external heat exchanger was found
to have no effect on the pressure
traces.
175..5
T10
176.5
T11
77+2
T12
74+1
T13
195.5
T14
110.5+2
T15
107
5
3)
IV-6
P1
10 mv. or
0.51 psig
P3
10 sec.I
Note: These traces were taken
sequentially and not simultaneously.
Figure IV-2A
Pressure Traces from XY Recorder for Run #2
(Subcooled Boiling - Taken on First Day Just
After Completing Run #1)
IV-7
cnoI
a
0
E
E -HI
o
o
LO
o* CN
o
r0
0
w w
O4
z w
4O H
U0
a)
U)
Q0
o
H
a) Eq
P
04I
pq
I
I
H
4)
-IO
U W
)-I
U(OQH
U
S-i\J
0
Hl
m
Cfl
E-i
r-q
H-A
E-1
BiTsd
T'O o
IL
_
I-
'Am
IV-8
O0
i.I
r44
Itl
v
-
-
p4
.
0
ll
-
.
I!
II - - i ---
I
!--
.-
..
.
--- '-.
Ie
N
0. m
03.
m
4 ..
I
.
II -:
H
'
'
-I
'
p4
,.
l
.
.
'
'.
--
j..
I
:
.
·
-r
0 H *k-.
tr
4-40
m
I
·'
- -
·
· '
....
·
'
.
_
T
-10
". '
0O
..
cn
CN
I
0
Joq
. . .
H
c,.
·I
a)
r
--
U)
U
(H
WO
::1 0
Ed
0 (U
E.4
0
-
·
r
'I
-
0 a
.41
NE-
''
* I
O t
-c-
-r
·
-
C:
:1
I
.
-- r.
i
r-
X
l
-- -
los
B
u
'---
.
-
4
-i
M $ om
w0
-
I-
--
a
C 4
i 4(U
.I
- I--·
i
.
:
.
1
.--
t
- -
7
EH
I
i :-if
.
i
i-Li-
- ..-- -
-.
-t-
i
I
''i
_
.
I
-·
i~-
I
--
. : ,
-
I
--
- .--
i
..
I
--------
.
- . I
I r'
P4
0
IV-9
o ...
0 Q.
L
0
#=
.-r
I-
-.
ka
:
-" '
'
n
w O
04
: · ·-· _-
L
O
0l
0
'7
·-- C
I'
: ··---
..
'.. ..
-·
limp
a)
'tP
:>
.1
I,,,
r1
t·--
i
I
1·
i ill
··-·
00a
14 I.)
0w
......
-- iCCe
i ·----i -i-_- i · j- -I--·
: 1 I---
··-
·-
L47
:1
·----
i·-l
'' ''
_:
I
i
cit-·i
1-
-
.--
L. 1
-1-
.II I
r f-t-cc
1 I
--:
(I· ·
: -··r
i
i--
ii
--
'
U)
Wo
WOO
0H
,.
--
'-
;
r -l
I
I.
.,
t
- - --
i
-
.--
I
, !
IL
.i
:
--
I
;·-
m
li
-
II
_
'. ...:i
!
IrI .
----
I
_:,.
i
IiII
I
_
I
II
_-.
A 0, F
*,,
I
.L
[
1
. I
. -. r
-,
i
.
.
i:.
,,.
.
i .,._--·.
i
-:. ,
.t
t
.
-i
II
-.. i
..
7-
1 1
-:.
.,
.~I
IL
.
--- --- .
PA
~-
..
4
i -
:-
-UI-· -
--
I
I-
t
I
4d ,,0 4
i--
..-
-- i--t
i
$4
-
i.
i.-
C)
I
b
H
.--Li-L
.
-I .
- -- ---
_L tt:.r.
.-
-
i
-i
IV-10
NC4o
I
0o
r4oaou
r
eW
I
-i
-
>
go
*0
ODN
W
N
I
~Om
)
w
H
U)
5.4
OE
-H
U)
[z4
o
1
4J
m
0
o4~
X
,
-r
Ui
P U
0 0 404,g·r
i
U')
P~
IV-ll
on the second day within 10 minutes after heating up the test section.
Figures IV-2D and IV-2E show pressure and temperature traces taken
the second day between 20 and 40 minutes after heating up the test
section.
A comparison of these figures shows that the pressure and
temperature oscillations observed for Run #1 (and for Run #2 on the
first day) did not develop until sometime beyond 10 minutes after
initially heating up the test section on the second day.
Figure IV-2D
indicates that the high frequency pressure oscillations occur at
locations P1 , P 2 and P 3 at about the same time.
Figure IV-2E shows
that the peak in the temperature oscillations occurs at locations T 1,
T 5 and T10 at about the same time.
Thus the pressure (and temperature)
oscillations at various locations were approximately in phase with
each other.
3.
Saturated Boiling (Run #3)
Saturated boiling was the heat transfer mechanism at the top of
the heated section for heat fluxes between 3 x 104 BTU/hr ft2
the CHF condition.
and
As the heat flux was increased within this range,
the following observations were made at the sight flow indicators:
Top. Above 3 x 104 BTU/hr ft2 bubbles became larger and were
observed continuously. Above 4 x 104 BTU/hr ft2 these bubbles
appeared to have agglomerated and the flow configuration appeared
more annular or semi-annular than bubbly.
Bottom. As the heat flux was increased, the spurts of bubbles
into the lower sight glass became more noticeable and more
frequent. Also these bubbles became larger. Above 5 x 104
BTU/hr ft2 only one large bubble was observed pushing its way
down toward the lower plenum every few seconds. It was possible
at this point to hear the oscillations going on within the heated
section.
Data corresponding to a heat flux of 3.83 x 104 BTU/hr ft2 are
given in Table IV-3 and Figures IV-3A, IV-3B, IV-3C, IV-3D, IV-3E.
The first four of the figures are pressure traces taken with various
IV-12
Table IV-3
Data for Run #3 (Bulk Boiling)
Power
Heat Flux
1.34 kw
3.83 x 104
Average Flow
BTU/hr
ft 2
lbm/sec.
Heat Transfer
Coefficient at 1,2
1741 BTU/hr ft2 °F
Average Tube Wall
Temperatures
Location
°F
T1
235
T2
235
T3
235
T4
236
T
231
T6
237
T7
234
T
NOTES
1)
See Figure
2)
of pressure and temperature
measurements (T1, P 1 ...etc.).
Temperature oscillations were
much higher frequency and less in
amplitude than observed for Runs
8
T9
T 10
232
1 and 2.
227
T11
188
T 12
73+2
T13
213
3)
14
110-111
(See Figure
IV-3E.)
Therefore average temperatures
were estimated by adjusting the
potentiometer until galvanometer
deflections were approximately
equal to either side of the zero.
Circulating pump for lower plenum
cooling was turned off and on
periodically as was done in Run
#2.
4)
T
II-9 for locations
5)
T8 was not operable.
No determination of average flow
could be made for this run, since
the exit quality was greater than
zero.
fTsd S-Z ao
*
nt
"
- II!
.Ur
r
IV-13
·.
Vtt
I
I
i
-
---
I-
\ i
___Y
J
-Ir-
__1_.
'72
0
_
-
i
_'
0
u,
-s
itl
I
-
- '
i.
!1-i·
U
03I
H
o
1-
CN
c:
U)
p
.
i··icZ:
--t
Pr4
i
1.1__
'S
I
I
,
:
L .
i-
.,
...
I
1
ii
i
i
r
I
_1
i
h_
.
.
1-=
I
ii-l
;LT
!
r
'rI-y
_
!.
-f-T-i-L-
-:i
i '
i
I
I-:it
i
--I
I
t
--- tL
I I
-
,
'
-i
-
:
.
!
.
-.
i
L4
0
-rY
a)
UH
U)
U2H
frsd 5Z jo
IV-14
Hl
P4
0U)
5n
m
I
0
H
a)
0)X
·r(
r-I
-v-
IU
La
4-
Ln
U0
CN
04
m
P4
IV-15
iTsd O'T 10
-AU
O
I
tm
.0
C)
0).
Ml
o
rI
U
I
H
a)
r
trl
-4
Q>h
rbC
0
r
acX
O
14Q
14r
0:0
6Tsd TS' 10
IV-16
m'AU 0T
IL -
-
I
Ic
- i
I
1
-- 4
i
-o
I ·
I
ii
9
!=
-""-
.I
I
-
; i
i
i
-l
_
0
TU.
j
C)
j7
I Ic
0
no
n4
H >4
0)
I k
H
>"-I
0)
0 t'
a)0
U) H
sm-
-I
i . .
P4
>3
r4
* 0
L
IV-17
LHrl 0
-l
_
__
_
i
!
.
'
.
I
.
_
.
.
r?s
o
I
I If
0
i
I-
---
: I
c;7
I
.
0
H. *L
o'
I
-I
-.
__
-
.I
7
H
0
'
j
__
__
II
i
I
__
.
.
.i
:i
i
1
I
I
I-
I . -,
-1
-------
:
i----
:
r I . cI;
I
T
.
.
i'-i
i
.
.
ii-
I
I*
I ''
.
Ic--
----_
i
L
-- I--p
-jI
-
--
:
t-
,-
U
I
I
I
E-1
i --
i _
I·
- - t--
iI
i
"-~Y
.i
1
I
-7
_ .'!
L :I
.!
_
I
I
--
-
0
iI
!
...
4
!,i
.
w
I
I-
-i f
If--- ~-
U)
; .
iI
. .. I
I
00
0
I:
._
----
0
I
.
'-I---- -
,,--
I
_
--
i
I
.rq
EH
$4
I-
IV-18
settings of the horizontal traversing speed.
Thus it was possible to
observe the details of the high frequency pressure oscillations.
Figure IV-3A
seconds.
shows that the period of these oscillations was 1 to 2
Also the oscillations at locations Pi, P 2 and P3 appear to
be in phase with each other.
Figure IV-3E shows XY temperature traces
for locations T1, T5, T 7, T 9, T 10 , T 1 1 and T13 .
These traces show that
the low frequency, high amplitude oscillations observed for subcooled
conditions were not present at this condition.
Only high frequency
low amplitude oscillations, probably related to the high frequency
pressure oscillations, were observed.
It should also be noted (from
Table IV-3 and Figure IV-3E) that Tll, the fluid temperature upstream
of the inlet to the heated section was substantially greater than the
lower plenum temperature due to condensation of steam from the bubble
pushing downward from the heated section.
4.
Onset of CHF (Run
4)
The onset of CHF at the top of the heated section was observed
at a heat flux of about 6.4 x 104 BTU/hr ft2
Data taken as this
condition was approached and exceeded are given in Table IV-4 and
Figure IV-4.
These data show that, for heat fluxes above 6.4 x 104
BTU/hr ft2 , T 1 oscillated over a temperature range that became
increasingly greater; until, at a heat flux of about 7.15 x 104
BTU/hr ft2 , the upper end of this range exceeds 9000 F.
For higher heat
fluxes T1 no longer oscillated and at 7.3 x 104 BTU/hr ft2 was fairly
steady at 11800 F.
Table IV-4 shows that at 7.3 x 104 BTU/hr ft2 , even
though T1 has gone through CHF, the temperature of the fluid leaving
the top of the test section is still the saturation temperature.
Visual observations at the sight flow indicators were the following:
IV-19
Table IV-4
Data for Run #4 (Onset of CHF)
Power
kw
Heat Flux
ea
uxof
2 OF
BTU/hr ft
Average
Tube Wall
Temperatures
(F)
T1
T2
3
Heat Transfer
Coefficient
at the Top of
Heated Section
BTU/hr ft2 °F
Average
Fluid
Temperatures
of (°F)
T1 1
T 13
0.45
1.29 x 104
208
214.5
1.07
3.07 x 10
217.5
224.5
1.37
3.91 x 10
227
237
239
2058
168
213
1.73
4.95 x 10
242
250
251
1500
195
213
2.07
5.93 x 104
277
267
262
1005
191
213
2.23
6.37 x 10
281
2.28
6.51 x 104
295-34.0
2.32
6.63 x 104
2.50
7.14 x 104
2.55
7.29 x 10
4
213
337
69
2362
173
208
937
213
794-513
213
318-430
632-306
213
518-904
234-103
213
1179
75
213
268
69-76°F
T14
107-112°F
IV-20
Table IV-4
(Continued)
NOTES
1)
See Figure II-9 for locations of pressure and temperature
measurements (T1 , P .. etc.).
2)
The tube wall temperatures given for power levels below 2.28 kw
are time average values obtained from XY recorder traces as for
Runs
1 and
2.
3)
The tube wall temperature at location T 1 oscillated over a range
of from 50 to 400F for power levels of 2.28, 2.32 and 2.50 kw.
Therefore, for these power levels the range of oscillation rather
than the average temperature is given.
4)
At 2.55 kw, the tube wall temperature at T 1 was stable at the
time average temperature given.
5)
Circulating pump for lower plenum cooling was operable for this
run. Therefore it was not necessary to turn the pump on and off
as was done for Runs 1, 2 and 3.
6)
The heat transfer coefficients at the top of the heated section
were based on the average of T1 and T 2 for power levels below
2.23 kw. For power levels above 2.23 kw, only T1 was used.
7)
The heated section was insulated with approximately 1/8 in. of
asbestos tape during the run.
--Ip-.I +
F--A
I
-:-: -:
t_._.t
CM
- --
t
r--
.,
- f --- .
- I
- i - - -
.
-
-
I
.
!
-
1:
-:
. :
I
_
l.
---
----- ;----
-
1
--
.
.
__.
:
:
i
_
I
>:_!
-
m-.'.
L
-- _
.
-
-
r--
1·
i---
,
T-f
.
ll
a)
a
---
*
.
.
<
I---"
|
.1 |
i
H
, - I
t.
O
,)
' H
i +t
0 ,
U
I
$
I
s:
-
:t
:
,
1-
O
'
!,|
E-4=
I- I: -
I- : ,I 4
-.-
'
11
_
---
t
+ +
---
-;
r
t
'
,
?:i
j -.,.
:
i·
I~~
f
t
,
-
.
1
1
I
;
4'i
1'
,--
i.,,,i
*
__+
I I l' !
| t++; ,- t1
M
! i
"
U
L
,
-!
-70
f~
,.- M el
1-4
i'
I4
. - -I
r-
·
r
·
.
.
.
.
-.
.__
1
·
--
.
S
,
_
l
_. a
.:i
! o
iU-i
UN
i-
-- ---.iI
.
- ·--
=" t--i
1 t
|.;
: .:T.:- ,-:-.,:.
.- ,-,-I,
|~~~~~~.
I
i|_ 1
.L
1
.
-
,,
I
.
I-
·
-
j,
: ;-.-I
.,
.-
---
_-I
t > -
.
(L
ul
Ul
-
·--
C~~i
4I- .
t
T r- I ,-_
:-- -;--
r
§
| |
_
6
----
-- · 1---
!
t
.,~~~~~~~
.
_+_
__
r t +lt
*
|
S
t
.
~~~~~'
'
'
|
-'
-:-L o
- gftiF
~I'-;-ir·, t i s j_+rLA_~~· -.- I-·--rt- II --·trf I-, | 4*
o
!0
!-.
I
t ii *'+g
4 4 ---- -- ---f
o4
--.
-'13
t--i r-l+il- -f* ` i -,r
t;. -
t
-,F:-:_:
--.
-
T
;- ; 1
§--
P .
!, r
1
l
|
.--
|
4
. :: :
-
-
,-
w---
|
|
--
|
i-·L
t
|
-
r
r
r
_
-- 1-
4-
-~- ,-:--
r-t- 1l- +. -t-+- .rt-Ir t -- I
I
[1.
-+-l --r,~_;It
I-~-
t
'
-t
-
'
4;
l
-t
t_
I-tJ._
,_--
----------+
-i
. .' __ ,f _=r
-
'1 '
.
-
;
d r-
_. _ . t
---
:---LT~t~
_ 1,'
l-,:
f~t ----
--
I
r
I
-f-
: 1-!Tr I
CN
--
;~,i- .
t8:t. __
. . ..
t-
..,
·
c.
|,I ,
I
I
-
i
I
S;
-
W
i i
l ii
4
L
.
I-1
-data."4C
ci'I t"' -
,.
tlie;
-
·- t· . ;
f
4
_
t
i -+1
t
r I
I
It
I
,
,
-I'
ii
i I
i
I
I- - ;
;
I
!
,
i.
E!
O
C)
· AUI 'buTpeaU
.··
TIT-
I11
.
I
[
1F
i
.
I
I
I:
F
i
i
,
-1 !~~~-- -- t i -·
-I
4-
t--t--,
I
.
.
.·
i±1t
,
'-4
tN
1_L.
;,
.
;
I, -. I-
| -
'
I- -
·
,
r-i
'
4
'
I
-
--
1
,
f
-I-
I 1-
-
n-
J
]
-1: -tE
,t-
i
1
·
r
i
rE
,
·
I
ru
I·
I .-
.~
.
- 4
,
,--
O
9Tdnoouagq
tit Li r%
-i
-r
Xtvi-iT-------i+·
-1
0
-LI
C)
-T-l
_
-1-_~i
t9~7
'-;~ i
I
T
.ir , '"'-"-H-:i-3--ItIf
,-c-m-c
-1:1Li- t-ttttmi t-+flt I-~i~al2t
I I I ii
;
i
T '.1
tj i
I I:_
1
r
1-
_t I
I
I
i-
If
-
ii|ri
o'ltl·r:i···
|
7
i
I
4T
I+-I't
I
-- -
I i
t
ttt
f'
· ·
:
-I~ co O
-,_ ~
-
,F
L.
-I
i
1
T-7
-I
r
40
. -tr-:i-- = tt-
i
t
1
1
t'
-
I-
.
r·---
l
M6
,
·
1:
·
· ·
L
----
-
.·
. T_
;
--- - TX
-t
_
, J--
-
jI
,,,,,,
LO
,
'4,
|
--
1 A t
.-- i
·
-
iI
--------tt
l
l
. --
_· :
--
,j
_
I
I,
I~I -t --t
I
_ . - ' IX
-,,iC
_
-
~
;
_--t-c
.+ _
I
_ ,
t
.` I
I.
--->X--T
8=|=T'
'-1
.; riTT -t
I -
I
r
r -- r--
:i , t-,
t
. - -r|
-t,
.-
.- e
:I
I-i.-
:
- -
---------
-
t
0
'ti-
-'--
I-~,
&! W
---
7'--
=
.
4.. I .+
|
g
|
I
,.
I - 1:1
: i!i
!! i
lerr
§
'
- 7- I-i t -,-t
f
jt
,
-
Lr)
- 1
i
_
t4-
tLli
.-
,#
~r-0
Q
s:tAk- C-<
g
.-
--
.-
t
-i
,,i
,
0,.C X
Ei
rr-I 4-)--I
4 E-
S
t--|
L
O
t
=
-tJ
t
.,
-~t---- --
---
I
1i .:,.:
[
in
E°., O , ·r
o
lX
|
~_
§
: ,,
i
-
---
A
.=__
+-
--
--
-
--
IW
rs-_
,
_u~z
f>
O 4
-rr
-tI~-~~1-
__1
.:
I
__
[---------
I,:
-
:
~~r~
-
, _,
- - t - , t'- -,--r1 I- - --- : - -- j . I T'- :q',
T7r*
- -:T-, , '=71
- -, -,
i-,
-~,
1 - :1
,. I 1 : -
- --
i
-·
|
: I
3 CM
-_ O
-: I
I III
i---llt~
t-
-
.I.-L-
T. .
r
,
<
:4
AS
-4-' 'U O 0
I
I
..
;
I
1- n-I
t NC -
tt
-*t---,+t
'4'+----F
tI
4 pg
.
-
7y7.
1)aUv
k
,c
I,. 4.) Ul
O
C
4.4 4-4 -r1
O 0
r-I
r---
-
'- .-
-
:
I
i
t
E
I
..
-- r
_-
:--.
I
-7
H@
-
o
,
co
ECmE
I,--
Nl
'-
---
t'
4
,A
O E- ra
*d
Ua)·r
D
1,-. ~
ul
-
-
.
v
i
:- .
:7-;:¢-i-
I
-, - I
--.
t L--
-
*
i-
k^
E X
u)
_u
::
-1,
-*-----t-I--,I-i:___
I -.I,
,.
(d
tp·r
..r-
I
----
:
U]__
(d C",
.i-) V
pD
W
.) O . E 1 ,.
4
--
S·
"
.........
1Q
...
t ...~--I
d-4
)
0
-
-:
.ttt
--
- ,
*_.,
Pi
t
i- I. 117F -
' ' - I
i
r--, . -1
, - . S.,-.
-
-.-7,---~- I
-
nrn
In
a) 4
4J
t::
_. :<7:
_=
_~
I . _ I
I-~
.
|
,
14
I11,
9?.
I
!,
i o35
C
N
0 &ll-
·
-- -I - ---- 1
.7
f ,.
r
~-=--~
---- c---
,L -.
-
: -.LU
·.
-- L__I-
4
1
~1:
t* __
--c-e
---
=
-1
.
-
Mi
-t---
-; :
- I- *4.
,I
----
r
.
.0
- -6
'
-- --- i
: . · · i--.
i
i
. .
.
0A
- O14
__i--"
.
4
?·; --1E4
-I~~~~
-_... -4.I:
e--
-----
IV-21
$4
-r
00 rcl
-
----,= ------ --i--·
1------
.
::
C
t
___
~~·~!c
-~
t
_- -
i,
:- - tw-:--
-- - .
.~
t
'-I
_
t~
--
4-
-- -4
------
I
-
--
--
:
_r
k
-
_
----·--
_---
:-
--
e,
_
.
-1 : .
- :46 -_-- ! : : , -
_
_
~
--
.
1
....
_
- -
-
-
{'tf:t-----1
- -!
- t-: ---4
-·-1
-i-
!:
:
-- - - ---
'
,
> i:-It--
i__
: ---,---
.: .
'
-t-
LO
-
.-
.
.
,
.
-
_
*
- - - -- I
---- i
__.
---
i}
--
-- --- tr- --
.,-A
-
1
,-
.I
-- --- '- 7
_
.
::
- .
t
j:i__:::---.:::.
.
-=i-
.I
f --.
'_ .-.
I: -
- -
-- t
;
---
,
_--
.
::
_
_:,
:
q
-L- -
-
:
t_
I
I
-.
I
-
*! .- !
:
-
I'--
-
I -
-
- T
-
I
Ei
-
'
_,I
-- --
-------- --- i-- --
.
I
i-
- - -- _
= r_
T
t
_ _ _
...
-- -- t --
- . -
-. _
--
t
f
. b
.
-- -
. . , ._
t
+-i
F.-wH
i -----
-
-
.
_
-- t
^ . ,
--
.~IL
. --:
- . -- -: I -
.
_~-
.
I-
-
!
[ -_
A
I
:
--
- _
F
- .
e
.
-t- --- -
- - - --- --
--
|
*· CO
-
- c
1---
)
t-Ln
-C4 4
_D
t
I
1W--=--
'4
i_
!
-
--
I .
;2 .0
(
I z
' i'-'.--
t
.0w rcl (1) U
iA rf%
Eq
IV-22
Top. Water was clearly present in the steam leaving the test
section.
Bottom. The large bubble observed pushing toward the lower
plenum in previous runs was now periodically disappearing below
the lower end of the sight glass.
B.
Transient Tests
1.
Step Increase in Heat Flux to Beyond CHF (Run #5)
After taking the temperature trace shown in Figure IV-4 the
power was decreased to zero using a knife switch in the power supply
circuit; and test section temperatures were allowed to decrease to
their equilibrium, zero heat flux levels.
Then the power was almost
instantaneously brought back to the initial condition, again using the
knife switch.
A complete temperature trace was not obtained.
the partial trace is shown in Figure IV-5.
However,
This figure shows the
temperature at location T6 as the power was first decreased and then
increased.
T6 is shown to reach its original level of about 5.3 mv
(2640 F) in about 10 seconds.
(At the same time it was visually observed
at the sight flow indicators that the original flow conditions were
reestablished almost immediately.)
After about 135 seconds the
recorder was switched to T 1 which was observed to be approaching its
original value as shown in the figure.
The power was then decreased
to zero to end the run.
2.
Liedenfrost Temperature (Run #6)
One test was run in which CHF was approached and exceeded in a
manner similar to Run #4.
increased
in Run 4.
to about
However, in this case the heat flux was
8 x 104 BTU/hr
ft2
rather than 7.3 BTU/hr
ft 2 as
The temperature at T1 was allowed to increase to above
1500°F before the power was decreased.
transient is shown in Figure IV-6.
The resulting temperature
This figure shows that the cool-
down rate increased sharply when the tube wall temperature decreased
L ,~ ---'''
-I!
... Z.
-.
2§,-" -_.·.__
...- .1
"-!
'. 4.
IV-23
i - ..
- _.
.
,
. ___ - __ - - - i __ - - .-.
_
. ...
..
i
j--
:
r
:- ;
.
:. .
.
( -- · ·
-I~~~~
I~
.'_ ..___. . _...
-::
::'. .:----- --F---------.I _. -:
,~-_. . :':
.. .. . ... .... l_ , . . .?...... .
t- t·-- ·-- i
: -. -: --- - : --_-.
_. . . . -I _
--- L--
.._
.
....
.......
.........
.
7 .
.
-
-
-
-
-
-
-
-
,
44
...
.
_
.
I
i
.
.
_
'
_
:
---4
-
-
.. .
..
- _
.
.
..
. i ..
.
.
..
.
.
- ·- I --- ·-
r
:_ .
-TITTTTt-
-
II
I
t
:...
.
4)
E4
t -.
,.._
I'
;
.
.
.
'
.
.
.
I
I.
.
.
...
__
.
_
_: ..
.I.. . ,
.L,
!
I
-
-
l
.
'.'...___
F
-I...
-
-. i ..
.
I''
i_-:-
- -
.
.
.
.
_. _'-.
- ! -i !::- g1 ; -4----T
.~ .. ,,, - .
I , - -7..
I i
-
..
.
I
.
.
. .:
I
.
I4 -
. _
-
*
I
f··~-- ··
. .
...
.. t
-- I
!,,
__-.1-.I-~.--.---- _
·--- .I---
...
....
-r.
'1
......
-.- 1- -.
___r
-- ,
...
,.----.-
::-::-:. o
...
-t. -
1
.
- . -::::i::::::
- .
1:::
....
...
.-.
r......
.-
;
-I--
~-~r.~-.
:-
i
-
*
.
.-
t
'_:.'
t
J
4-
i-4.
_,..
-
. t.
.
I...
'
.. _
u3
oo.......
...
-'-:-=
.. .
.;-
S_;
,
r
. I _
-
_
*_ t -- -- -
1 i
---
·.
-: :--
.It
- I.;
w.
_=J...sI..
_.,._ --
-
-T-
-7
- .7.'F,
,:I
. .
E-,I
-I
i- -,=..E
·;L· .
!
i
::
.
. : t-
_
__
._..
.
'.::
:t_ . 4_.. ..
-°Xtj0, -:t_:-i'.
Lt
.-.
X_.
'_.-
(
-
-
..
(
.
;. -I
*
... i. .
ti
I- P:;
I . ..H -11.-r:Ai ....-'
.- -I - -- - 1.
!- -.' - | , .-... T- , 1-,
I f .4.
-,. : -+ . -- i
i·i·i-l
t` i
i-i-: : -I;-·---i
__ - -r - -- ·· I·· :-!:-··r-l;-'
i··-l-·
.,-- ' .,I "'lj
--"·L
:·
:
1-- --·1---- . · '-'
:1 !!
I--· · - ·'·' -·-:
I · ·-- -- !-· -·: ,. ,
1
1
1 7_.
-.
:....
.. 4
_7
....
_
:
. !
.-
t _
t-t1 ...
--r
l
.
,
:i
.
:; I
_
.
_
;;
L
04 r
t
.1
_
I
o
,tO
Or*'' '
.I- .. :.
1._
-_
.- j I - - II -.-:.-::
i. *..
! :'i,!:
-.'- i
.
E
.
-
--
-r
s
---
" '
. I
-,____-
i T ··· .
·
. ..
--- i
i
I
I
-. N
....
.t I
.
:-!-. ;---r --
..
';
.
I--I1 :3
1.
i
--
7----
H
W
o~a
I-I
P4
MO
a
'
''-: '.:-:---4'',
r,-t..-?'_:
__
Ul
Co1
U I
I11
- E-I
4)H
·d
-7-
__
.-
:_
I.n
14
IQ)
I.o
::h
.
. I..
.-
4 a
1-44
b 6
L
O
'! ra
4
i-
:E4
H
0
I. . t
1. --- 4-
BW
:1
T1-'l-
J
.-
3
-i
rL
;
-
. -·..
(L
! :aqM~
_,.
-
a ru
,-;-,-f
.H*-/
i-7 t. --
·
t :rr
; 4,.
.1 . :
-. --:
*I''1 -!
'
r j_- 1'-
_t,
°
t _
,
_
--- ;.·
.:
....
i
E)4
13X
T.
10
.. . . I_:".
.
.. I
·.
_
I
i
_'.:-.-: : : : ,
..
-
--
O
Uit
._ . ! : =-
.
._-.
't
a,
t
-
*
I,
_
_
-4. -
I
-
. . '-'.
t
-
'1_
t.
_
10
.
L
+r
.!.
i(
_.
.....
M
,I' U
.
It
t
·
·
._
.
:::7:::, ::::::..::It .
-. -
':...-
_.....
...........
:
._,
.. .. J . _
·-
_ ;I
__
:1A
.- -
-'..
•
-
..
...
.
........
X-
.
..
r-.
.. f_
....- --
t-:
.J.
---
r
-
i-- ,:
--iI -:_:--·. t-_
- i*4 ,q-i I- :
- -.
--
. . _
---· · I··---+----
..
_
-4i 1.e l
,_.
0)
0
-·----·--t·
-------
i
-
--.-r- --- : -:'h-.1.
:
L.-2,-i -
.,
.
_,
:_
_,1 ...
___~
. ---. I
--1 ... L__= I----_.
I... .
,
"-!-'-.
--- , tT:.~T
r
.1
4.-
r
4--
..
I''-, --
. .
r
t . t
.
!: 1
.I
,.
j-
..
I
'-'"
-:
... -'I
7
'--: - . -- j-:
.....
'. ;~
.- .--
-
...
,
.
:
--t
'.
IW
.I
'
1 -i
'. f-I-:
. :''-. ,:_I:
[:-L
- -Tt.
''':::-:
:~1
-1
__:
.
r----
!I .
:
.
'..
c----C -
_
;
I
-. :
...
.. :.:;.
- t:..
. .
.
---- -- -..
....
¢
. ..4:
-- .
..
t·- -· -:
-
1
-=
_.
- ----
- - I
__:1
~-
.
.
*'-
44
Il
,el
.
... . ..
. . .. i._;.,.
.
-· . . ., t.-
tt-
.
-
~~~~~~~~...
y
.
....
.
.!- .. . 11 L
. ,I_: -_ -.
_
_ . ._ - - ., -
I
.
I
I
1:...
-- .
:'-'
| :-::
. . I ' . : - · i-.--:.
*.
EI
I .
..- -- -
-l
. . .
I...j
T ;
.
(·i··
··
.
L_
_-.-t, .
r_-
.
. . . ,,
-
I
I
-- :-
a
. ..
:.:
..
,:
\-
·
--
:'
------
:
~~~- : - +."
::- --:'.!.:":':
:'_r'"m"'-t;:':: .:.j
- --
i
-[
:
- -
- - i
I _ . _.
:!-;--:::-:::..
___ I.
l
I
I
f
1 - - -. ..,9 .f . .
...,I-_
L:-.: . Ij - "
tJ --
..
::. I!:t:_ 1: :I.- :_. . .i :'-,-,r" tt:
...
:--I
-
.:
. .: . j :
.i·l·-i·
. ..
.
_._ - .4 . ---
I:
= *_
-': .: ' I . : ; .
1I -
...
.
-
·
,':....
~t . .- J...
--
-· -
--- r·------ t-- · · - t
I-·-- -- Li
.
__
_.
..
.
---_IC_
I _. _
-
i
----t
.
'· -- :.'
-.
':. ... :'· i--::-=
i ....
N- r--
I...
- t- -
..
.
.
::-'
1-·--
. .....
_..
'
i1 -
.:::::::.(_:
..
-
..
.
W
-- :- . ._=..I-
t
G
'1
...· : ·--
i ·- - · i · ·:·I
-·
'. .,i
. .-. .: . I. . . f.
.::t.- I ::. --[I.':''- :.- : ^'*- I-1
_.
..ii- , · .,.' .1
-- -,
_.
_
_
: -.' . -
_
-1I
;I
.:.
___-
H.
- r - ---
.
.
. _-_
' ''
i::~:-:-.:.
=
1 . ..
,
.
_.'
T.
....
- - - -
j
'
:.-: -'-..-_.:-:-
- .t, '-'. .- - - .-- t .. .. ---.-4 ____
-; - -- t
, , - -,
:-.....
I . :|:-:-: . i - .'. .i. . ..
,._ i
|
..
_
.. . -. - .
-
-_ ,_
.. .
-. --
-.
I_
-c--c--
-
.....
I..:.
1
-I-·--·
th
...
·- ·-I
`--
-
r----
I
.
:--- --- -- . - i
;-·
___
. '
.
.-
....
:
-- --
_.. I
.. .
_-:. :. . .-t...... :.-...
... - i f-:...
!
.:
.
t-··
t
.... :I
'
-.
. .....
I·
i_
_
.
_--. . -.- m.. .
; ?:
i
..
:::::~:.::
--:
--
t
.
.
:
,
_
. : .........
T. ,-"""
...
· t
.:
. . .
__1_. - __
.
.
': _
!
. .
---if--:
:::-::
_+4-
·-
..
+-
1
.,..
th
. . 'i
_
....I.
-. `T---tTTT773-
..
Ij.
I
----.I-·.-.
1:
..
..
...
:
-
:
:
:.
I
-
:.
1.. .
..
... .
.. I';......
''
:.
ij
.
.
......
.
..
T__
..
.
.
.....
.......
:
:-:::
--:.-- - L__---- ---:-4
:'":
.
- ::-
..
.
.
.
.
.
_.- I I I -,. .- -; - - J.
-;
t-l-- "`
-1.
----
E40..-
-f
....
--- ·--c... .....
-
:
!
:J
iT4
I,.I
P\DO
O
IV-24
.rz
Ej 0
LO
00
i
-
,
r\
.1
C'4 Ofl
.
-
,
I
- -
Ir
-)L
I
I
i
_
, __
:i=
_-
.
-
_
_
__
_ _~--
.
.
_
_
-1_
_
i
---
I
pr4
--
|
_F
`----
^
,
,
_
I
i
i
------
I-
V r
n
m r.
_
.
i
I
i
_,
T---- ----
/
J'
I,
r-
-
CN
4J
4-4
----
I
I
-1
l
.I
I
-
-
----
I-. -I
k
I-
-
I
i;
t' '
'
'
0s-4
I
3
0
3----
. .
I
I
I ,
0
(o
I
1-
i
. . I
-i 1
I
I...
:
- 1*
I-
i-
i
-
. IC
. I.
-·
I
1
I
7L4Il
I- T
-- L----i
I
~
--
I
:
I
.
-ftc:~
·
:--
I
I-
i
*Ht f-
:
i---- I
I
I
IU
r I
V3
I.g
II -- i
I
.
H PI
i
I
:i
fI
; l
J
I
I
_
g
I
.
i
--
I
l-
L
I
.. i
i
--
_~--
L_
t
.....
.___---
-
__- - - t --
i3
r-
E
X.
I--·
I
I . I Ln (14
- ,i- i 1
IV,
L"
IE t i
i Ii
-T-
o
H
a,
1
---.7
t
I
ilf)
--t---7-
-- i--t----
-
o
I
l
i
-----
,-
-4
_
I
A_
---,i
.
,,
,i t'
i
I_.
--I
x
i
I
I
_-
l ., +
- 1
..
.
u
.
i
44l
IV-25
below about 9000 F.
This is apparently the temperature below which the
wall can be rewetted.
This is consistent with the results for Run #4
that indicated T 1 no longer oscillated once the temperature exceeded
about 9000 F.
V-1
V.
ANALYSIS AND DISCUSSION
A.
Analysis and Discussion of Tests
1.
Flow-Pressure Drop Characteristics of Test Loop
In Section II.B, the following equations were derived from
conservation of mass, momentum and energy, assuming one dimensional,
homogeneous flow of liquid and vapor in the fuel assembly or test
section:
L
Agc
dW
dt
dL
W
dTm
)
[(PfPm
dt
PfL14+7mL2
2
~~ g
Q = hfg pgA
[ Pm
)
dL
dt
P fLl+7m
L
D
]
(11-8)
I
I
(Pf-m)
3-I)
=
0 2%- [4f(
dt
+R
D
2
pfA
p
2 ,
dT
L2
(II-9)
dt
Whfg(Xout
L2b
1)
where
L1 +L2
1
m
L2
PmdZ
JL1
R
1
I
L
+L2
1Pf
-
(-)
dz
JL1
Pf
Pm:
l+x
-g
g
and
L1 , L2 ~ are lengths of the single and two-phase regions
I
I
L1p, L2q are the equivalent
lengths of the single and two
phase regions including effects of inlet contraction and outlet
expansion
V-2
It was further shown in Section II.B that, for steady flow and
uniform axial heat flux distribution, Equations (II-8) and (II-9)
become:
= (Pf Pm)
L2
f
c
W2
LlL + j L2 )
[4f(R)c
-
2~ g
D
D
2
pfA
(II-10)
g
Q = Whfg(xout-x)
*
where L1i,
(-)
!
L1 , L2 , and L20 are related to the boiling length, LB, and
!
!
L 1 , L1 , LH, L2 and L 2 by the expressions:
0*
+
. vo, 1*=
L1
(LHLB)
= L 1 + (LH-LB
)
(II-12)
L2
LB + L2
2
L2
= LB + L 2
and LB is defined in terms of mass flow rate, inlet quality, power,
heat flux distribution and LH by:
LB
L
Wx1
Q/hfg
(II-14)
Equations (II-10), (II-11), (II-12) and (II-14) can thus be used
to determine the steady state flow-pressure drop characteristics of
the test loop.
This is done by first performing the integrations
required by the definitions of pm and R using the previously given
approximation for Pm and the following expressions relating quality
to axial position, z, under uniform heat flux conditions:
Q/h
W
(z-L )
LV
LH
Li < z < L + L
l1
H
(V-la)
V-3
Q/h
x
+ x
L1 + LH < z < L
+ LVb)
Then, substituting the results of these integrations and Equations
(II-11), (II-12) and (II-14) into Equation (II-10), and rearranging
gives:
Pf gc(L
+
2
)
t[1H
+D
H
W
LH+L 2
L
D
(LH+L
)2
L
+ (1LH
+
+1+
where
2_
_
LH+L 2
LH
+H
(V-2)
LH
) +
(1 +
)
H
2
']H+2
LB
LH
+H
H
L
2PfA2g9
+HL
H
2
Xout
XoutX 1
xou
t
Pf
)
The left hand side of Equation (V-2) represents the constant
external static head driving flow through (LH+L2 ).
The first term
on the right hand side represents the test section static head loss;
and the second term represents the test section frictional head loss.
Thus, on a graph of AP vs. W, the left hand side of Equation (V-2) is
V-4
a single horizontal line.
The right hand side is a set of parabolas
for which the variable parameter is Xou t .
For a given value of Xou t,
the steady state solution of Equation (V-2) is then the value of W
corresponding to the intersection of the parabola representing the
right hand side and the horizontal line representing the left hand
side.
Solutions were obtained in this manner for the test loop
conditions for values of Xout between 0 and 1.0, as shown in Figure
V-1.
The numerical values of the fixed parameters involving test
section geometry and fluid properties were obtained from Table II-1A
and II-1B.
These values were the following:
pf = 59.8 lbm/ft
3
x 1 = -.146
Pf
= 1603
Pg
f
= .0055
D
= .152 in
A
= .0181 in2
L
1
= 10.5 in
LH = 36 in
L 2 = 48 in
L 2 = 55 in
Since the test loop was operated at constant heat flux for most
of the conditions studied,it is useful to convert Figure V-1 from a
set of parabolas representing constant values of Xout to a set of
curves representing constant q".
This can be done by using the
following equation derived from Equation (II-11) to determine for a
V-5
Ln
000
C4
Oo) a00 o
o) o) o
Ln
0O
-I o
-
9N:.
1__
! -11IL."' -7-
77:! i.
...i'
lib
i .·
i
--
:...
m
.;
.
___
i!:
i : i.
W
\
._1
IX
.1* ·
.i
-
· ._
__ - t
__C__
, II
,I,,
______·
k_
- .
....
-- -- ,L--
I4-I
.
......
.,,.,
. I.i
I!
--. --4.i----k L__-_ I ,tI
: . . .
i -
:i
i...
I
I...
H I.
I__
. . .· i -
-'.
oc(I
7-
__·
,D
H-
--r-
-'-'I ---
--
'''
c-
'7-
!~ii i i
... :-
I.-
I.
4-
-- -·---
7I7
7 -:
,-I
.:
If
UQ))
-7-
···
.T:
I-..-c
CJ
,-I
..I
· ·· ·
----1- :.
-7-
77
·
i:
-- -
''`'
n
···
I
77-
`*'
Nt
--
·'
·I
ILC· ' ' '''
m~-
a
I 4J
0
a)
·· '''
I .
i.
;;.;
·· · ·
77-I-I.
·'
00
Ic
I
: i
·
-··
....
...
--t
·--- ·----I
i
-
i-
I rij
'
:::
II,
x
·:
i I
I
'..:
--''
'''
3
s
i
+ii
i:
I ·I
i' ::
r;`7--I~
0
0
LA
011
Eq/Jq
CL( 0
·- --·-
· ·--- ·---
CN
----------
irij
'1111
TT
00
M'
I 'aV
00
C
C))
00
-
m
D 4
Q.lJ
0
--
i.f
rl
·Y
04Sr4
M
H4Of
4.1
Q
-I
-I -H
U) 0
I.
···
·i·---------... ;
- t·
- ·
----
3 ,U: -IJ
4r
4-)
F. -H
m
WD
-
---1tr
1
lt
. 1
-.'1
1,0
*'
--
. i
ti
:' : "--
C",
i'-
Z
.
.::
00
:1
'7F
i -
t-I.
00
:1
·'
; I
-
-I-
i~!1i--
····
L.,
: 1i
no--.$
..
,-I
*.----
i
:I
o!I:::
-
... i : .
i :i
.,
-Id
f
7t7
---i--'---
-·-
i;Y
·'
·!:
i ')
.ri'4
I0
il
--
7-7:
i:
00
H
N
a
4
0 )
------·--
0
0
V-6
given q" the values of W corresponding to the various values of
represented Xout in Figure V-l:
q"DL
H
= Whfg(Xout - X1)
(V-3)
The result is shown in Figure V-2 for values of q" from 1 x 104 to
8 x 104 BTU/hr ft2
1)
2)
3)
For heat fluxes below 3 x 104 BTU/hr ft2 there is only one
steady state flow rate satisfying Equation (V-2). This
flow rate corresponds to a value of Xout < 0 (subcooled) and
is stable. (Thatis,amomentary decrease in flow rate at constant
q" causes a decrease in AP which causes flow to return to
its original value.)
At heat fluxes of 3 x 104 " i4 x 104 BTU/hr ft2 there are
three steady state flow rates satisfying Equation (V-2).
These three flow rates correspond to values of Xout between
zero and 1.0. However, only the flow rates corresponding
to the lowest and highest Xout are stable, (At a flow rate
of 5.4 x 10-3 lbm/sec a momentary decrease in flow rate at
constant q" causes an increase in AP which causes flow to
decrease further until the lowest of the three stable flow
rates is reached.*)
At heat fluxes of 5 x 104 BTU/hr ft2 and above, there are
still three steady state flow rates satisfying Equation
(V-2). However, only two of these three flow rates correspond
to values of Xout between 0 and 1.0. The third corresponds
to Xout > 1.0 (superheated). Again, the intermediate flow
rate
2.
From this figure one can observe the following:
(and Xout)
is unstable.
Subcooled Boiling (Runs #1 and #2)
a.
Summary of Principal Results
Steam bubbles due to subcooled boiling were first observed
at a heat/flux
of about
1 x 104 BTU/hr
ft 2 .
Above 1 x 10
BTU/hr
ft,
the heat transfer mechanism at the top of the heated section appeared
to oscillate between a condition approximating single phase convection
and subcooled boiling.
The onset of bulk boiling occurred at a heat
flux of about 3 x 104 BTU/hr ft2
.
Data and observations for this
range of test conditions were presented in Sections IV.A.1 and IV.A.2.
*See Reference (5)for a good discussion of flow-pressure drop instabilities of the type indicated for this solution of Equation V-2.
V-7
0
I, [LI7--
- --
---
-I
i
I...
--E
-
i
_
-
I
_ ___
-
-
t
-
iF
1
--_
--
Iq
. S_
I
__
: :1.
CO
--
I ---
I
p .....
-
-i
'
v
|
O
--4--
__
C)
:
H- ~--' ,
_
I
I.
-
. I,
.
;;I-
I
---
iT_
I
_
-i
_ - _-
-
I-
:1
-
.
-
L_
v
I
7.4
i
.
...
-
i
-e
i
1
1
I
I ii
..7
':
,I tO
-
q-c. i - i. 1
I~·
'
''
I
t
..
4i.A_
i
I
0
f.
CC
I I
. .
r-
_ x 1.
_
-7
":T
oH
t
_
Is
-u
-he-
;
i
c;
t---
cc
__
s
._.1.
'
_-
_
_.a~--t-j -
.
S
r
.,
---
i
i--
Ix.
.
--t
_._.
V
I .I
-
-:
.
_-
I
-
--
------ --
---it
t--
-
:, i II. :-- : .i
I-Ci
--
jI
=
:.
.
-l
.t
_
':
.
I
,
,
TV- - .+__
If--
LL
.:i
:1.: .
'--L--
I.
l
-I--
i---
i
:
j
Lj
l
i
i
-
.
T~
.
' x
1ThTEL-
I
.----i-,--,
.
77
CY)
1
-
-
t
i
'i
-:..
iI
7-
-
j
:
kk
N
() r
OH
X
V
-I
L
il
I
-I-
- -
...
0)
H
Q)
--. 1-
.
-
. -,. . I:
l
Io
--.47
----- T---
--- -- --
Ho
-
Io
_
:T :
ill
ow
i
H
ID
x
l
I
:
-
0
L--
I
'
-lT
,TL
t-
_
-t
_ __
l
--F--
7--T--
-r 1 ·
_i1
1
:-
-4
, 1, .its ;
I',
.
--F~
---
I
_ T_
U)
rL-
i:
,,.
N4
U
wQ
~,.~
- 7
1-N
r
--
I
-
. .i
LTI
i
i
-
--
--
-
i
-i
rx
,.,
-,- L
-
i
,
i
I
-l l
-
,--,
-- i
..
I
.
I--l*
-- ,
-i
--
T-·
1
-
.-- 6,.-
I-
---------
II
=
0
o
00
'
.
i
I
II
-I
.
0 "r-x
--
- i,
I
-_fc;
0- .-
-
__--
7_L;G=m
--
00
'
iiii
I
I
r- 1t
t
-
0C)
Ln
:--
A
I!i
I
'-
0C)
-- ·-----
i'
--
±,1
'
0
I'
1
,.
0C~
zi/Jql 'dV
&
.|
0
0N
0H
V-8
The principal results are summarized below:
1)
Small bubbles were continuously observed at the top sight
flow indicator. However, these bubbles were probably
largely due to noncondensable gases initially trapped in
the test loop or dissolved in the water; since, as will be
discussed later in this subsection, the tube wall temperature
at the top of the heated section was only periodically high
enough for subcooled boiling to occur. Periodically, the
flow would appear to slow down momentarily followed by the
appearance of much larger bubbles over the next several
seconds. These larger bubbles were probably due to the
onset of subcooled boiling. The time period between the
appearance of the larger bubbles decreased as the heat flux
was increased above 1 x 104 BTU/hr ft2 .
2)
The test section pressures were steady except for high
frequency oscillations that were observed for several seconds
at regular intervals (see Figures IV-lA, IV-2A, and IV-2D).
At a heat flux of 1.04 x 104 BTU/hr ft2 the time period
between occurrence of these oscillations was about 45 sec.
and they lasted about 7.5 sec. At a heat flux of 1.75 x 104
BTU/hr ft2 the time period between their occurrence was about
15 sec. and they lasted about 5 sec.
3)
The tube wall temperatures within the heated section oscillated
continuously as shown in Figures IV-1B and IV-2B. At a
heat flux of 1.04 x 104 BTU/hr ft2 the period of oscillation
was about 45 seconds; at 1.75 x 104 BTU/hr ft2 , the period
was between 10 and 15 seconds. Thus the period of the
temperature oscillations at each heat flux was about the
same as the time period between occurrence of the high
frequency pressure oscillations.
4)
When essentially the same test condition at 1.75 x 104
BTU/hr ft2 was investigated on two different days, it was
observed that periodic high frequency pressure oscillations
and the corresponding temperature oscillations were not
observed on the second day until the loop had been operating
for about 20 minutes. Apparently a flow disturbance or some
other initiating mechanism is required to start the cycle
of periodic subcooled boiling; and, on the second day it
took longer for this to occur.
5)
At both 1.04 x 104 BTU/hr
ft2 and 1.75 x 104 BTU/hr
ft2 ,
the average tube wall temperature increased with distance
from the inlet to the heated section (see Tables IV-1 and
IV-2).
At 1.04 x 104 BTU/hr
ft2
the temperature
at
Locations T1 and T3 (near the top of the heated section)
was 208 ° + approximately
100 F.
At 1.75 x 104 BTU/hr
the temperature at the same locations was 217F
approximately
b.
ft2 ,
+
60 F.
Analysis of Temperature Data
The variations of average tube wall temperature and fluid
temperature with distance along the heated section for 1.04 x 104
V-9
BTU/hr ft2 are shown graphically in Figure V-3.
The same variations
for 1.75 x 104 BTU/hr ft2 are shown in Figure V-4.
For each of the
tube wall temperatures plotted on these figures, the maximum and
minimum temperatures resulting from the temperature oscillations are
also indicated.
In Figures IV-3 and V-4 a straight line is drawn between the
inlet and outlet fluid temperatures.
For a steady flow, uniform heat
flux condition the fluid temperature variation would be linear.
However, under oscillatory flow conditions such as observed in these
tests where vapor generated within the heated section is periodically
observed to force its way upstream, this may not be true.
In the case
of the tests described in this report, this is almost certainly the
case for heat fluxes above 3x 104 BTU/hr ft2 since steam bubbles
were periodically observed at the inlet sight flow indicator.
However,
for the subcooled boiling test conditions at heat fluxes of 1.04 x 104
BTU/hr ft2 and 1.75 x 104 BTU/hr ft2, the amount of vapor periodically
generated and forced upstream was much smaller and probably had minimal
effect on the fluid temperature variation along the tube.
Thus the
straight line variation shown is probably a good approximation for
these conditions.
The fact that the average temperature at the upper end of the
heated section was only 2080 F for a heat flux of 1.04 x 104 BTU/hr ft2
raises the question as to whether subcooled boiling really occurred
at this heat flux.
But, in considering this question, it should be
noted that the temperature was about.periodically 100 F higher than
this.
Thus the wall superheat was periodically as much as 6F.
The amount of wall superheat required to initiate subcooled
boiling can be predicted using a correlation such as the one developed
by Rohsenow and Bergles (6). This correlation is based on experiments
V-10
co
u'
wr
I
I
I
I
I
I
-4
__
- -
r
7. -.
i 7-:
I '-'a...i.
:
I
i..l
;
i
-
r
·
-
..
I
V-\I
I
I
,I
IZ1
·h
I
-
-
!i .\
.
8 iB -I
-
.
---
o......
I.
1
.
---
P-
-
------
-----
-
D
---
.
-- -- -o I
__
-i
_
l
.
-
: --
-
-
---
-,
.
1,
!-
-t
r
-
d--r-~t
_
----
LL
¼;-
-I-t-
I :
..
.A
----
I
_
--'! -
.
.
4
0W
0)
d
L'
'--'''4
0
- 1
I-i_- . I----4-
6dk.lmhA----_
+----·r--
--
_ !....
1.,
-'I IT
-]-
--.
I
l
I
II
kO40,C:
'77
-77
) mN
·'
J
7-d
.:
-: :
t
--I
_ .
._
·
-.::\l .'
.
.
:
_
'4;
--.:1- - :1-'
-T
-r'
4J-1
'i
0
.!
-4kr
H 3
(AI
.. I
.,.
.
p. 11
L. .
.e-- ,.. I
:1 -
cI
·
i
i
.--
I. -
-i
.I
. .1':
1 :1'
t-t
i--I
- .
i
..
.
- --
i
.7
._
O
fil
T-
---
L
----
: ! t:· *|. :'|··
_,
.
,,
0C)
_
.. I
4-!
1: 1..
I 1:
1.: .1:
-
1
..
1:-:'
I
I .:
I ..
tt
ii ±~~~~
t 1- .
-4t.
4-)
Uo
-d
1. 1'':
1-. 1. .
-i-'i -'~
. :I
*
---
-
_
1' :
-__T
t-rtr
. _-
i i
.
J
I---
-
..
.i
.. .
: __
-
L
I--I--
~-
.,
------
I|
T-
v.
-
A
. I i
.,
SA.d
.-
' : I '
_
1 .. 1
~~~
~-I
It
-.-
. I - I
- 7 __
s
......
IL -:1
ri6s' -
..-
7 . ..
......
.
..........
T_.:
. ...
.-
H
4D
I
,
|
.
I
....
,
...
i
--
i
.
..
...
,
I
I
.
..
I I'
a---1:
.I
. . .
E-4
Pr4
,.
-7
::
'1 :
tf·-ii_
_Lt-
-I
I
,
_I -
--- -.
I ..
.7,
:'
-
.
-
I
.
.
1
-
-
I :1i
-
.. .
:
7 7: ' ___:
. |
t
. .
i
4_.:iii'
.: :.·
....
In
a
,,
;..
.1.
I
0
N
,
.7I
. I., . -::::
-- -.
E4
0.
--
IL
.
.
. .,i
I
d
0
'· . i·
..@
.
.4-
I
. -
4.
i
. I
. I
. .
,I :
I
I-
--
.
.
-
E) i
---
X 0
Hi vi 4w
.
k
t
-,
'
V., :...
.
7-
---t--1
----
H4)
. . . .
tI '
,
-i
- T--- I
:
_. .. 7
m
--- 7---
_
I
::
0I0
En
i
:1
...
e---
---
i
a)
C
C--~ --C
4 ..__ ----
_
I
.
ht------.-.
0
0
.
-
r---
.
:
.-
I
.- ---- · I-
S-
--
* . I1
i -
f '!
-- .-
-
i
4) O4
r
l
-- ·
-
7-~- 7-
4
-..
i.
i-_
.
I.-
.--
..,
t-----,,
i-----t--
{
I
men4
-
--*i
.
_; .t
l
t
t1
.a
-7
--...
.
, .
0
Hl
a ' anqeadmea
0
Hl
-1
LO
Ln
- -
...
77
O
V-ll
F-I.
I
I
N
Ft1
f:
I,
i
I i
Wd
Ci
.
..
-- - -l
- I- . . II . .. 71I
:- : I::
Ll:
---*'
.
:
·-- _
.
__
._
i__ _ MM-
-
'
I
1';
._
0
I
ad4 cfl
f_
!
E
U) O.
k ·0
.. .
...
i
....
7
.7-'
. ,. I
_
,
...
::A
.. :
.. .
..
: :: i
-- ·
.,
..
...
.,
..
,
,
.
.. I
\
,
,
...
.
,
.
,
.
..
. +
.'. . .-7
...
..
,
..
,
.........
r
,1
co
ka)
;
Q
a)
- ;:
|
..
,·
i
..
§
.
.
a)
,: a
-
.
.
E
,4.)
0
:
.
....
I
'
. I
I
.
:
....
---
r
i *.
.
I
.
.
.
1:::
.
|
,
,
1:
'
m.
'1'::
. :1
:
.
.
.
II
.
|
.1'.::
...
,
.
....
.,
....
:
*
..
|
:
:
.
: I
.
I
&,
|
.
}
:
..
.
....
.
F
.
..
Ir
....
_.:1:
,
.
::.1.
::
..
§
....
iC'".y'''"'
,L q
,
..
.,
,:
:..
....
I::
L.--L
- .-t-.1:'
:
I
,....
.m
-:-p
*{~: :I7
L-
I i ·;
: ....
i :
11
.,..
I~~~~~~~'
I
I
ji.
777
---
.i
I
I
-
,,:~ ;iI'i
.. ..- !:. .S- t;
,
i-
:
iW
-
.
C~kl
:
. . !
,.
;.z,
....
tI
: 1,
0
o)
ol
e4
I
,i ~
_ :
i
1:
i .
. .
i,
rt: .
|
-sr;
...
.. ,.
I
Vii
] i: , i
IfrT::l
,
O
o
I'
L,,,
.1-..
1
_
,,.,.*'
-.'
i7 :
.-7
i
It.
r
±!i
I:,
t.-
'
: ::
'111
. .1
m'it
i.I
I
1 :-7
... i
7. -
72:1.77
1-1
T.. ', I :-: , I
-: ,L.-
'
. 1-'-
! ...
7-.
:
.I
,..
-_.
0LO
i I Ii
I..
:.
1':
'1
I
:;
.. !., ,
; ;;-
:. :;
-: · :
H4
*.o ' axnsaduai
·.
I'
o
H)
.1
.
iI i
;i
1: 1
.:;
L::- . .I
i: · ·
'zI
a)
4-4
I . .1 .:
: : : : i..
'A'
I4
;;
....
{
.i:t
'
.,
I
I
-
.
.
4
#
....
l
,
:7 ·
i.)
(a
_
.
..
,
.
,1
L .1
L
_.
,
I
n
I
__E
t
* F
...
.
::
....
....
i
:
:
.
1
1::
1'''
--
I
.
.
1:.':
.
. .. __
I
§
,
...
1'''
.,
.
,
,
.
il -- r
t
.
:N
:- 7
.
4
a'
:
1
1'
ra
t
:
. _._
t..1
.
:
t...
.,
,
7.I
ft
I
,:.';
.
....i
- 1
. .. __4
_.__
I''\
,
l...
§
...
'::1:
.:
:,t;::
F_.I
: II i .
I
t.
.
....
.
.:
r :::
·
i-7
.
:..
-te-:
ti :t
.....
.
8?7
I
--
4,
. .
,
...
W-
---
.90
0
. ..
Ell
94)
.
.
..
i.. t
..
.
.
i,::
---
. I
-11
.ri
...*1..
:1
...
..
ee
X ........
:i
···
,
.-
r-I
1
I ..
1..
.
. ..
...
.....
I
,
'
....
-
-.
.. {..
I.
.4
,
..
I -
::
'.0
to
..
l;:
I-r
.H
.
I
.
,
I
... .
.
.........
I:.
, .
·
t·- ·
..-
4
a)
H
H
....
..
I
t
!....
0
.mr-I
.
:...
.
.
.
W
L
.
··
r·
)
nn
0
rz
.
..
......
_
.
·
s
4)
pk
7-_
-t . ..
i
1-
,,..
1: ·
i-
.,_
En
.F
H
...
,>
.;....· ' i' ';
7::.
--: ...--
---
.
..
_:1
.
.;1.
{
,
,,, :
i
I
. .....
. ..
.......
......
..........
T vT.
:!: !!i:·
- · ·,
.;:,-
.
..
\
··
N
..
.: *L
,
,
i:j
m...
·
.,-----
__
...
.. . :
:. ..
, .
· · : : I':
1-C -1
.Hj .---r
__
4.)
rcl
:'A
f
--
r--
i
-I
*re
: ...
....
....
..
t--
. :. .
,
-7.
..
---
. .
.E .
,.
.
_
t'
...
.. . :. ..
.
,
I . :·
':·
'I
·· ..
'.:
. .,
l ,-4
H (d 4
"r-1
.
.: .:
''''' i,::
.
·
I
.
.
. .
:.
....
i' i
_
_
L.
7 -
,...
H1)4,'
..
:-
i
.... 4H.
.,..1.
;I -.
:I
.
. ..
:. - I. .::: __i
. .,
..
......
, . .
_
_
-
I. .
S
--I rl -i
W
_.___
__
___--
_.....
- -. -:
_
-t-
. .i\.
.
_--
t' .
.
-o
-----r---
__
'-
__-.
1:
:l-' '.
I....
d-11,.
77-
iH U X
I...
:.
. . .
)---- !-
_
-
i1: .-
...
...
I
I
I
I
7--
.....
·7
' '
______
|
i- -
I
-7
-Hl
----
-U)
:
.
:.'''7'
tt
q
' I
.
!----I- t--·
I
-_
__-
l_
_
i
,I
::
!
.
I
:-
".i
V 7'.
..
I.
, .
a0
.
F-
..
.-
I-
_ . Mi'
- P
I':
-:I '.
_.. i .---.
:
ld·
6W1::' 1!;
1!L i!
1 im d
i: -.:ii:::'. l
o
IL
.I
-v [ I
-
'!-
_... .
! '
0(n
(d
El)
-H
V-12
set up to determine the onset of nucleate boiling for water over the
pressure range 15-2000 psia.
The correlation is given by the following
equation:
qON
qONB
15.6 p 1
0 0234
sat )(2.30/P
ONB-4)
5 6 (AT
(V-4)
where
..
2
qONB
=
the heat flux in BTU/hr ft required
for ONB (onset of nucleate boiling) at
(ATsat)ONB
(AT t)
= the wall superheat in 0 F required for
sat ONB
the onset of nucleate boiling at qONB
P = pressure in psia
For a heat flux of 1.04 x 104 BTU/hr ft2
and a pressure of 14.7 psia
this equation gives:
Tsat)ONB
Thus the maximum temperature reached during the observed temperature
oscillations was sufficient to initiate subcooled boiling.
The value
of Twall corresponding to a ATsat of 4.80 F is shown by a horizontal
dotted line on Figure V-3.
For a heat flux of 1.75 x 104 BTU/hr ft , Equation (V-4) gives:
(ATsat)ONB
6.10F
The corresponding value of T
wall is shown by a horizontal dotted line
in Figure V-4.
As for the lower heat flux the tube wall temperatures
near the top of the heated length were periodically high enough to
initiate subcooled boiling.
In this case, however, it appears that
these temperatures were high enough for a greater portion of each
cycle of oscillation.
Also shown on Figures V-3 and V-4 are two lines parallel to the
assumed linearly varying fluid temperature.
The line nearest to the
V-13
fluid temperature gives the wall temperature variation predicted,
assuming a constant heat transfer coefficient along the heated length
obtained using the Dittus Boelter correlation (7) and the mass flow
rate obtained from an energy balance.
This Dittus Boelter correlation
applies to turbulent flow and is given by the following equation:
hD
0.8 0.4
f = 0.023 Ref
f 8Pr f
where
(V-5)
4W
Re
ffDpf
f
fCf
Pr
f
-
kf
The line farthest above the fluid temperature gives the wall temperature
variation predicted assuming a constant heat transfer coefficient along
the heated length obtained using the following expression:
D = 4.36
(V- 6)
which applies to laminar flow through a vertical uniformly heated tube
(7).
Figure V-3 shows that, for a heat flux of 1.04 x 104 BTU/hr ft2
the above correlations give tube wall temperatures that bracket the
measured temperatures, indicating that at this heat flux the flow may
be close to the laminar-turbulent transition.
The average flow
calculated from an energy balance on the heated section is 3.7 x 103
lbm/sec (Table IV-l), which gives a Reynolds number, Ref, of 1950.
The
range of Reynolds numbers corresponding to the laminar-turbulent
transition. is 2000-4000.
Thus, the flow may have been laminar at least
part of the time.
Figure V-4 shows for a heat flux of 1.75 x 104 BTU/hr ft2, that
the measured tube wall temperatures fall closer to the Dittus Boelter
V-14
equation, indicating that at this heat flux the flow was probably
turbulent.
For this test condition the average flow calculated from
an energy balance on the heated section was
gives a Reynolds number of 2490.
4.7 x 10 3 lb /sec which
m
Thus the flow probably was turbulent
most of the time for this test condition.
c.
Analysis of Flow and Pressure Information
The average flow rates determined from an energy balance for
both 1.04 x 104 BTU/hr ft2 and 1.75 x 104 BTU/hr ft2 were higher than
predicted from the analysis in Section V.A.1.
Figure V-5.
This can be seen from
This figure is a graph of the steady state solutions of
Equation V-2 as determined in Figures V-1 and V-2.
The stable and
unstable solutions are shown in Figure V-5 as a function of heat flux
and quality.
At 1.04 x 104 BTU/hr ft2
the predicted flow from Figure V-5 is
2.4 x 10- 3 lbm/sec, compared to the 3.7 x 10
an energy balance.
3
lbm/sec obtained from
However, the analysis in Section V.A.1 (which was
used to obtain Figures V-3 and V-4 and therefore Figure V-5 and the
predicted
flow of 2.4 x 10 - 3 lb/sec) did not account
the periodic occurrence of subcooled boiling.
for the effect of
When subcooled boiling
occurs, the average flow would be expected to increase due to the
increased density difference between the down-commer and the test
section.
As a first approximation, one could take the average flow
during subcooled boiling to be approximately the same as the flow
rate predicted for the onset of bulk boiling.
Figure V-2 shows that
this flow rate is approximately 7.2 x 10 - 3 lbm/sec.
Thus, if it is
assumed that part of the time during each cycle of temperature oscillation is spent in subcooled boiling (with flow at about 7.2 x 10-3
lb/sec) and part of the time is spent in single phase convection (with
V-15
--:
.-- -- i -
I
I
-
1
-
I
-
.
-
.
- - -..... I:
..I :
-
:-
!
i-
:O -;
GL m.
.
I·
--
4-
t
1
I
.
o
II
...
J
.
__
__ ..
.......
_
__
._
L-
_- l
___.____.
_ _
__
_ _ _
_
-__
l
l
·--
___
--
,)4
.
-.
. -.
-'- - - -
_-
___
. _____
.
\: ':!i':-i.
---...
ma
I.14 -- -.- i - a . ---':..
1.N
L
...
i '.
r.-~
[: .
-
.
.
i i
--
mi
-
- -
_
_
l
_-
.
-
b
ki0
H^
I
-
i--
.
__ 1-
--
--
l
-
-S-
3
--
i
N
--
I-r-
r.
o0
Hl
_<
-
4J
i
.
,L i":
1
-
-
7-
-
__
. .
_ .
_..
_.__
r-I
-:
1 1
O kw-
-1
'.:
__
as......
r-l
.-
-
....
--
I-
__
-5
. sJ
.. ._
.
.
.
: I-
.
-'=
-
_-
:-
......
!
:.-
.I
.... .:
I
. .;::
O
-
-
T--
.
-K-->
..
04
0
m, ,
: ...
....
I
'1-
'
·-
· ,·· · ·
''
"
·"'''
Ul
O
0
·' '
· ''
"'''''
'''
· ' '
''''
"'
,:::
'''
' ''
'f
''
..
""
' '
`
'''
'''
"
''
' ':`
'
' ''
'''
'''
I; 1
'"
"
'·
...
to
--
61I
...
-
;.,..
|......
SIN,
.........-
j. i..
::;-1:
S
i:i:
c3
--
-
·'
'
--
7'
1::
:;
'
i
;
·I· ---t
O
4
·-
;.'
-,
1:
.:.'
'
!'
.
..
.
.
..
..
..
.
..
.
---
':
..
...
r
''
.
..
l
·:
1'':
.
_ 'f
i ::
.
,
'':.1
.::::...
-
,,J.- ,
.
f-T
··1
I'''
'''!
-e
... :
r·t
...
·.
1t
·
C
'-
.,.,.....
.
..
II : I
·(
..
....
···
! ' ' '
i
::' 'ii:
SjE1
:t
·'
?
.
.. ,
..
H
!--
jl ij
',''
-..1.'''''
*'r'
.. .
.
.
777,
.
· ''
i···I
i::j
t
· · ·,
. .
I
0¢
......
z
·' '
-"
41
n.4
: :j
i
...
i
! : ...!!
,"... ... i ....
-I.';"` i +1
,.X.:.s
i:
"'l
i;
;l
,
;
-.i-l''~'
t:
I
|
I
-f
t
|
'
.';
-1--
|
~t
:
· · I·
I
.
-
·'
:::
-
:I
tt
--
-· -
t-
-
_
-
'
'1'
.
1
-
''
:-
'
,i :I
--
C4
'b
U
f
-I
i
·i
-·t
r II t tf-I
'
LI
0O X z; .l/fsl
r-
-
-e
· · ·t
----
Nj
I.' '
4L
00
77
li:
-
O;
C)
···
_.,.
. r'
V.-
:3
··
- ·
-e
...
,
XF
:· .·
C1I
II
X
T:
rI
tii: ;.. __
.
a,
7::-
':
::
0
4p>
I
.
ki.: !,
.. 1
CN
Tj-T
7-77
k:
:;;1::1:. :1;
0Ic)
·.
.
"'
I
. a:
... I
...
:"'s
ll-;'
i.''
: I:
-'· ''
"
:;I
:'.
. ..
:
..
...
..
.r,
. . .:
'
7
a:
: ;. :
. :. )
"'
...
....
S.,.
...
t:'
T'TT
ILC
II`' I '
,-
'-Ti
: 3r
0)
rrrr
O
V-16
-3
flow at about 2.4 x 10
lb/sec), the expected average flow would be
given by the following equation:
W = FlW 1 + F2W2
(V-7)
where
W
= the expected average flow
F 1 = fraction of one cycle of temperature oscillation for which
flow is single phase
W1 = the predicted flow rate under single phase conditions (2.4
x 10- 3 lbm/sec for a heat flux of 1.04 x 104 BTU hr ft2 )
F 2 = fraction of one cycle of temperature oscillation for which
subcooled boiling occurs
W 2 = predicted average rate for subcooled boiling (assume to be
the same as for onset of bulk boiling or 7.2 x 10-3 lbm/sec)
Then, if it is further assumed that the high frequency pressure oscillations shown in Figure IV-lA are associated with subcooled boiling
and this information is used to obtain F1 and F 2, this equation gives:
= 5 x (7.2 x 10- 3 ) +
45
45
(2.4 x 103)
2.4 x 10
)
= 3.2 x 10 3 lbm/sec
=
3.2 x 10
compared to the 3.7 x 10- 3 lbm/sec obtained from the energy balance.
For a heat flux of 1.75 x 10- 3 BTU/hr ft2 the expected average
flow calculated in the same manner as above is:
5 (7.2 x 10 3) + 10 (4.1 x 103)
15
15
= 5.1 x 103
lb /sec
m
compared to the 4.7 x 10- 3 lbm/sec calculated from an energy balance.
For a heat flux of 3.07 x 104 BTU/hr ft2 (Run #4 - to be discussed
in Section V.A.3), which corresponds approximately to the onset of
bulk boiling, the expected average flow calculated from Equation (V-7)
is:
W = 7.2 x 10 -
lbm/sec
compared to 7.3 x 10 - 3 lbm/sec
obtained from an energy balance.
m
V-17
The above results are shown in Figure V-6 as a graph of predicted
average flow rate (from Equation [V-7] and data from pressure and
temperature traces) and average flow rate obtained from an energy
balance, both as a function of heat flux.
Also shown on this figure
is the flow rate obtained from an energy balance for a heat flux of
1.29 x 104 BTU/hr ft2
3.
(Run#4 to be discussed in Section V.A.4).
Bulk Boiling (Run #3)
Summary of Principal Results
a.
4
At a heat flux of slightly above 3 x 10 , the fluid temperature leaving the test section became equal to the saturation temperature.
Thus this heat flux corresponded approximately to the onset
of bulk boiling, in agreement with Figure V-2 and the analysis in
Section V.A.1.
BTU/hr ft
2
Data and observations for heat fluxes above 3 x 104
were presented in Section IV.A.3.
The principal results
are summarized below:
1)
Above 3 x 104 BTU/hr ft2 , large bubbles were seen continuously
at the top sight flow indicator. Above 4 x 104 BTU/hr ft2 ,
these bubbles appeared to have agglomerated and the flow
configuration appeared more annular or semi-annular than
bubbly.
2)
At 3 x 104 BTU/hr ft2 , spurts of small bubbles were first
seen at the lower sight flow indicator. As the heat flux
was increased, these bubbles became larger and more frequent.
Above 5 x 104 BTU/hr ft , only one large bubble was observed
periodically pushing its way toward the lower plenum.
3)
Above 3 x 104 BTU/hr ft2 , high frequency pressure oscillations
were observed continuously. At 3.83 x 10 BTU/hr ft2 , XY
recorder traces indicated that the period of these oscillations was 1 to 2 seconds. (See Figures IV-3A, IV-3B, IV-3C,
and IV-3D.) Also these traces show the shape of the variation
of pressure with time from cycle to cycle is quite similar.
4)
At 3.83 x 104 BTU/hr ft2 , the tube wall temperatures were
between 2300 F and 2400 F at all thermocouple locations along
the heated length (Table IV-3). In addition, because vapor
generated within the heated section was periodically forcing
its way upstream and condensing, the average fluid temperature
entering the heated section was 1880 F (even though the inlet
plenum temperature was 720 F.
V-18
)w
C4
En
a)
isw,
__
_
I
...
-+_+___
_____
-
----
-t -
.
._
_._
t----
I-
tO---
I- -.
I
f-.---
t-- .
-
_
-!
__
t
0d
,L.
t
fi
l
ll
.
.
l
_,
;
i
- i
-
rd
a)
cl
a) o
____1_
- ____
.
a)
, .
__~
L
0
IO>
:
.
,
8
---
v
! tA - - -
- - oO U
(d -p
I :
..
i
I
,
.
C.
Jd -W0
iI
r
.
I-
_r
--
:
i
I
T--__
-
-
-
-
--
-- I
I
-
;
±
iCd
1I-c-
t
L-.>
h
w cd
V.
k
.
_._._
_
_-
__
I
._
J,'---'--4'
-I
i
_-
__
I
---
_1__.
,
--t-- --- •
Ij:
--
r
_
I
!
7 ....
-
m
t---t-
-
_
a)
. t.
F
I----
----
--- r
_r
_
--e k4
E-
is
0
4-.
i-
)-i 0 --
En
o
a)
E0
""
I
--J---
--`-*
--
I
---
0
I-
"d a)-.
4-i
.I
. I,
o)) w 0
-a
co a)-A
-I1.
I
F --
7-
-
,o
. .-iii- ..
____ _
1
. III
. 1i.
'.f--
!
U) Q
04
.o,-
0
I _
--
-
.
i-
----1----
--
! ,i I
__i_..
o__ ..................
r-
i
t-
---- 7
rI
-1-i
--- i---
7--
-- i-
L-
i
---
-----017
<1
_
7--
7K
.Ie
D
---
-
-
1-- --
C-,
---.-- (
7 N-
l
-i
'-
ry-
ci
::
--,- 7
-li
..-.,.
_I'
, .
_ .
7. -
-i -
-- L-
I
1-- 1--
- 1 ---
-..
: I -- -
I
k4
i
-- LI, I
-; .
-I
I
CN 4s-I
...
-- I-.--I
I.. 4._~
1
~
i.
-- t---
-7-
--t---
r
--- 7---
-----
I
-7-
,
---
't
I---
C-H
H
~
x
7--i-
CN
--- 1 I
--- --
I
i--
1\ 4---.
--
· 0 -I 44
-.
-7- --- - --
7i-
---
-- --f
-- -- tI_-
-4--
1---- I ---
.r.
i
I
II
Or
1 'i',
I , i
7
0
a)
I
-
I1:
---
_
-1
. __
:
c*
..
1. .
i,__J
,
1: I
...
,:
I
:
t
_
-
,...
..
: t
,-'1
.
S-
-
T-7-
rr-·-
13-1-
'',
!,.
!
.
_
I .
l
ti:i
l
_
,
.
.
.
I ,,,
t--._.J i.. ;_.J I
-- 7-r---l
i
i
(.
Ll
0£ x os/uqi
"'I
I__
1---
1--
1
. ._..._ I .,
(N
'M
tr
-77Ii
_
il
K,
I'
!------t
I .
L
.
oNs 'I
_.J ___..l
-
_N
. rx
_
I
I..>
o
0
V-19
b.
Analysis of Temperature Data
The average tube wall temperature measured at the various
thermocouple locations along the heated section for a heat flux of
3.83 x 104 BTU/hr ft2 are shown graphically in Figure V-7.
shown are the inlet and exit fluid temperatures.
Also
The average tube wall
temperatures range from 227 to 237°F corresponding to wall superheats
of from 15 to 250 F.
This compares with a (ATsat)ONB of 8.80 F given
by Equation (V-4). The tube wall temperature corresponding to this
amount of wall superheat is about 2210 F as indicated by the lower of
the two dotted lines in Figure V-7.
The upper dotted line shows the
tube wall temperature predicted for fully developed nucleate boiling
according to the Jens Lottes correlation (7):
1 /4
ATsat = 1.9(q")
e-P
/ 900
(V-8)
where
q" = heat flux in BTU/hr ft2
P
= pressure
in psia
The tube wall temperature predicted from the Jens Lottes correlation
is 2380 F, in good agreement with the measured temperatures.
Thus,
fully developed bulk boiling appeared to exist at all thermocouple
locations along the heated length except near the inlet.
The fact that, as the heat flux was increased above 3 x 104 BTU/
hr ft2, an increased amount of vapor was observed periodically forcing
its way toward the lower plenum and condensing indicates that a
substantial amount of the energy transferred to the fluid within the
test section is periodically transported upstream and transferred in
turn to the colder water upstream of the heated section.
This is
verified at a heat flux of 3.83 x 104 BTU/hr ft2 by the fact that the
water temperature leaving the unheated inlet section was 188°F compared
to 720 F at its entrance.
V-20
lw
I
co
I
,.
W
P
~~
'I-~
~ ~~f
r
__
--
__
J--.----
.____
.
O
.4I-"
I
toX-P
4
-I M
· il .c::
._
_ -
,
.
0
m
i·---
-
t
---
. . . ...
- - , -,t , . --..
i
1-'1---'i-
i
..-.4·----
r---:
'.:-
--
c-
I
t--
.-.. .-
t-t
.,
-
:
t--
... '
-rl
. .
-T'.-
--
...
I
..
I .. .
....
i
I
...
1-'.
7--
...
..
.
i
I
I.
I..
-4
H
:
I.
I.
t .T
t
[--
-*-.I
. .m
0
1--1--:
t- --
------
i
-- ·- ,--··I.
7--
4J
U)
... 7'
· i-I
c-
i ·
....
. . .
- -- ---
Ii
i
*
-I
..- · I..
------
..
j
--- t-·--·
t·
I
-·-- -i
------
!
*1-
i :-
.
: I
.
-,
---
1--:~T-
0O0
I
-.i1-..
m
I.
.
. ,I
p-
---
i
- I_
--- · i---
. . 17 -
'_
-14-i--·
.·:.C:...
-
. .,
''--t
--rt--
.
II-·,--
.
I
-
---i----
1--:- f -. f
. T
--'---
W...
,--
T--. . I.
EI
i
I
t
.f
-
.
i
.;·-
-- I---
I
0X
ti
......... --
-i,
--
.
.
i.....
---
_
-- - --. ----
I
.71
0,
1
bt
......
.
- .
r'
_
_
_
_ .
I
[i
.
o
__
I
-- 7 7 7--+--7
,
i
.
I
.--.....--
__
- . .. 4--
I _
I
i
.
_ _...j__.
----7'
-t
.
.
--- 7
9
rlW
.__
.
t
.-
---
C-
_
.
i
I
_--"-"---
_
54
0
i
!--
.
I
__
______ r-
-
It
---
--
+--
0
-- "
.. r
-7-1
i1: -,-I
...
S. .
0
E-1
3 d M
---7:
,
.
...
'
_ 4!-i
._-
_._
'--
F--
t I
_.
. .!.
,.
--i
1--.'.:
I1. .. i.
....
r--
i ;,i
rd
I
-
...
.1
_
0LA
C14
- ii ---
....
!f'_l
-
-
7·--
: ··
-71
.-..- 7
''''
,''::t:
__
-
..
:t.
...
: . m:
:, I--I
f---,
0C)
. 7--
...
...
---- 7
.. 7 --
I
:: i
; ·:
0
,-
-- I
j.lenqadma
1.i .
I.,.
: m:
---
0
.:
.
-'7-.-
I
.
-77
' ' ' . m.,
I
-1----
I·-
I,
.:! 1
_.
---
I--
..
I:
_.
...
.. . .
n
-] F-]
a: , .
...
!..7.
-.--77
...
00
m
1.I
t--t--
...
..-.
l
O
i:t
. _
i
'7-:
-- 7:
L-
-V.'''
I_.
.
::r
.
-i -- · f--;
_
-
"'
.. . . . .. .
:
.t.
_ _
,
.
L
.......
-.L -
-
.I
_-r--
.
.. i
i'
0
'i:'
t
I_
-' 7-
_t
,
CI H
.-- i--I ·
'
...
0Ln
O
0
V-21
c.
Discussion of Pressure Oscillation Data and Observations
The pressure oscillations shown in Figures IV-3A, IV-3B,
IV-3C, and IV-3D were observed to occur at about the same frequency
as the appearance of steam bubbles at the lower sight flow indicator
(every few seconds).
Thus, the two were probably related.
In
addition, these occurrences were probably accompanied by oscillations
in flow through the test section.
A possible explanation of these
oscillations, based on consideration of Figures V-5 and V-2, is
given in the following paragraphs..
At each heat flux above 3 x 104 BTU/hr ft2 , Figure V-5 indicates
that there are two stable flow rates corresponding to each heat flux.
The highest of these flow rates corresponds to a low quality exit
condition and the lowest flow rate corresponds to a high quality
exit condition.
Figure V-2 shows further that the range of stability
near to the highest of these two flow rates is very narrow.
For
example, at 4 x 104 BTU/hr ft2, a momentary decrease in flow from
the higher stable flow rate of 9.4 x 10 -3 lbm/sec to below 8.5 x 10 -3
lbm/sec would result in an unstable flow condition and a further
decrease in flow toward the lower of the two stable flow rates or
1.4 x 10- 3 lb/sec.
Figure V-5 indicates that the corresponding change
in exit quality would be from less than .01 to between 0.8 and 0.9.
However, the periodic appearance of vapor upstream of the heated
section and the continuous oscillations in pressure suggests a
somewhat different and more complex sequence than this.
Specifically,
the appearance of vapor upstream of the test section inlet indicates
that an increased average void fraction corresponding to the low flow,
high exit quality condition is achieved by steam pushing its way
upstream in counterflow,rather than by an increase in exit quality while
maintaining cocurrent upflow.
Also, the continuous pressure
V-22
oscillations indicate that, whatever the sequence resulting in a
decreased flow and increased void fraction, the situation is quickly
reversed, resulting in a return toward the original high flow, lower
void fraction condition.
Therefore, it is clear that a strict quantitative interpretation
of Figures V-5 and V-2 such as done above for the case of 4 x 104
BTU/hr ft2 is not correct.
Nevertheless the following qualitative
facts derived from these figures still appear valid:
1)
For a given heat flux in the bulk boiling range, there are
two stable flow conditions. One of these conditions is a
high flow, low quality condition and the other is a low
flow, high quality condition.
2)
The high flow, low quality condition tends to be unstable
since only a relatively small, momentary decrease in flow
creates an unstable situation resulting in a further
decrease in flow.
Starting with these facts and considering again the example of
4 x 10 4 BTU/hr ft2 , one can then return to the part of the previous
discussion where the flow is assumed to decrease momentarily below
8.5 x 10 - 3 lb /sec.
m
When this condition is reached and the flow begins
to decrease further, the amount of vapor generated within the test
section increases.
Apparently, however, a condition quickly develops
where the rate of vapor generation is greater than the rate at which
it can flow out the top of the heated section.
Thus the local pressure
builds up and the excess vapor pushes downward through the heated
section.
At the same time, the liquid flow into the test section
decreases and the void fraction within the test section increases.
Eventually, enough of the test section is voided so that the steam
being generated can flow out the top of the heated section as fast as
it is being generated.
However, this flow condition is not in thermal
equilibrium in the upstream half of the test section due to the presence of a substantial amount of subcooled water.
As a result the steam
V-23
in this part of the test section begins to condense and the water flow
into the test section increases, causing still further condensation
and a return toward the original high flow, lower void fraction
condition from which the transient initially started.
Then, since
this flow condition tends to be unstable the sequence begins again.
Assuming that the two flow conditions between which the system
oscillated at a given heat flux are approximated by the two stable
flow conditions indicated in Figure V-5, the average flow was probably
somewhere between the flow corresponding to these two conditions.
However, because of the way in which the low flow, higher void fraction
condition is achieved, the exit quality corresponding to this condition
is probably significantly lower than predicted from Figure V-5.
Thus,
for a given heat flux there is probably more water present at the top
of the heated length than predicted from the homogeneous model.
4.
Onset of CHF (Run #4)
a.
Summary of Principal Results
The onset of CF
hr.
4
occurred at a heat flux of 6.4 x 10
BTU/
This corresponded to a test section power of about 2.25 kw.
Data
and observations for this test condition are presented in Section IV.A.4.
The principal results are summarized below:
1)
Flow conditions at the sight flow indicators were substantially the same for all heat fluxes above 4 x 104 BTU/hr ft2 .
As CHF was approached, the large steam bubble observed at
the lower sight flow indicator appeared to be periodically
pushing its way into the lower plenum.
2)
The temperature at location Tlat the top of the heated
section was first observed to oscillate at a heat flux of
6.4 x 104 BTU/hr ft2 . Above this heat flux, T1 oscillated
over a temperature range that became increasingly greater;
until, at a heat flux of about 7.15 x 104 BTU/hr ft2 , the
For
upper end of the range of oscillation exceeded 900F.
higher heat fluxes T1 no longer oscillated. At 7.3 x 104
BTU/hr ft2 , T 1 was fairly steady at 11800 F (see Table IV-4).
V-24
3)
As the CHF condition was approached and exceeded, the
fluid temperature leaving the top of the heated section
remained at the saturation temperature (see Table IV-4).
Also, water was observed to be present at the top sight
flow indicator.
b.
Analysis and Discussion of Temperature Data
Temperature data from Table IV-4 is shown graphically in
Figure V-8 as a function of heat flux.
The temperatures shown include
the tube wall temperatures at locations T1 , T2, and T 3 (near the top
of the heated section) and the fluid temperatures at T 1 1 and T 1 3 (inlet
and exit of the test section).
For the temperatures that were observed
to oscillate (Location T1 at heat fluxes above 6.4 x 104 BTU/hr ft2
)
the range of these oscillations is also shown.
Figure V-8 indicates that, just beyond the CHF (defined as the
heat flux at which large temperature oscillations were first observed)
of 6.4 x 104 BTU/hr ft2 , dryout of the tube wall occurs.
However,
rewetting occurs periodically; and, at 6.5 x 104 BTU/hr ft2 , the
maximum tube wall temperature is only about 60°F above its pre-CHF
temperature of 2800 F.
Apparently this is due to the water periodically
entering the test section as a result of the pressure and flow oscillations discussed in Section V.A.3.
As the heat flux is increased
further, the maximum tube wall temperature reached during each temperature excursion becomes greater; until, at a heat flux of 7.15 x 104
BTU/hr ft2, this temperature is about 9000 F.
Above this heat flux,
rewetting was no longer observed; and, at 7.3 x 104 BTU/hr ft2 , the
tube wall temperature was relatively stable at 11800 F.
This result
indicates that the maximum tube wall temperature at which rewetting
can occur (Liedenfrost temperature) is 9000 F.
Independent verification
of this is discussed in Section V.A.5.
Figure V-8 also shows that, above a.heatflux of about 3 x 104
BTU/hr ft2, the fluid temperature at the inlet to the heated section
V-25
I1|
-r
·I
1.
.
.
...
--
+
t
.
I.. . . .
-.
._::
..
. F
.
,
.
.
. .
_
...
EsO
.
.
.
. -.:.--
.
·- t
,
-.
---
·-- -
---
f -I-
· ·· ·-
..
'·"
CLI i
-,-r
-
i
-
... .4
__V .
L'f
f''rt
f"'
?
i.i
r-,
-
-
-
t-
o-
1·~-
.
. .
.
to0
4) rn,.,
Id F
4 4lrOdr
I E-
.
_.,
.
_
-- t--r
.
.__
_
....
L
Ic! f
I
---·t
··rt
___
-. _
-Ly
.LLI.L
-i
--
tr"r-
--
-it
,
.·
+-
U
_
,--
.
_
...
-
rarb
-
---
_
----
___
.
_.
__ ._
_n
.
.
_ ___ _.
.,
.
.- r
I-cC
_4 4n_
-.r
.
I-~-.
-.
_ -I.I
t:
'
I
--
+
.
--"-:'
--
_:
---
-_
I
.-
I--·-t
'
_
tf-
r
oa
,-!
I..
'._'
1: i
f ;-::
1',-:--
'l .
.-.
,-
0
· · r t- -- ·
- t ' '-"
::t:
----I--·t:
--t'
--,..,
.. , .·
- ----.i
C---
--
.L.r
· -··;-t
.
.
·--·-·---·
-·- · · · - t ·---
m
1
j
71.i
_-
_._
t:)
m
--,--.i
.X.
._
E44
-------1-·
-·r··.··
t:
T- 1-L
..... :.I·::
.-. ·I---t---t;i
.t
-.
1.: :--.-
tI.........;
!-
.-
I`-...,.
4-.L
---:1- 1-
;I..
.-
1_t _:
.i
_
1--
---'-·-1·-'
'"''
-·--'
,:"" __:-
'
i::-
_
.__.....,
.-..
---
...- '-
t i ·· ·
... ....-
!. --. - - :-
r... -
.
f--i
-1----
.I
1..
1l . ...
;'
-I i-_
. -it
.L?" ,
---- · r---·-.: .:..
--,
--.
r: -- -
rr''
- IN -
.I
ii_
'''
r_4
i
- ----it -_-
.t--·-'-:-··
-...
tl
O
Co
aO 'anqlaqdtu
-; i
.:-=
t_ = :,
oo
r.
.:
-
--
.
,
I.
'
oo
r
C)
_
..
_._
·
·--- (----·
; ----- I
:.-:.!
* . ; : ,:i. ,
-T,* i- * *
---
-1.
- . : .-... .
1....,1,.
··
LI
--r_:.·.i.
N
-;-I
:-·
'
-t-·-·---
. ....
.
_t
r-i_;
...- I.
i 1
..
--
w
rt4
Nx
M
_,_
I·Ib
.=
T rl--....
....
.. - .i__~..j
-A. 1.... .... .I .
- 1
·- ·-t
.~ .:-i-
h..
-j-. ....... ;
-.-... i-t
'i t-: -·,·i
rtr ·- ,
t-r+-t·
·
i,
·I
':I;
_'
-:.:.!
'_ :.:
·
.
-r-·-t
. .
Ir
!
----·- ·--- ·-
IlO
I
.-i .-. ..-
.. .
--- lt
·--·-- ·
·--·--·.--.
-- ·
· · ------··------· ;
--r-·-'-'---c-.r·
L·._·-+-·:r-
.
.
·
.-
- ·
--
---· ·-· ·--·-·-· --·-Lf-
·--·--... .
..-
..
X
CV
.
_;.....·-
· :
-: -tC
-----
i---';:-. ....
I-L-
--- -
rr---
i
.·
:
' '-t
- _.-F,-..
Ln
..
?-
r
7 ?.
--t-. - 1. .
iri.
.
7.
I''
I{:..
----
[TT
I
,
---
--- !,--
.
.
Pk
.::
._:.._.- -
[ .1 ......
r;-
I
___
._,_.
_.
;-_,~.| .-. :] :._..
_ _ 7 _-__ __ .
·-· L
r
. ..
-
--
.....
,-:-'
::'.
./
...--T:.- : :t|. .:::[
:---::i
1-:
W_
_l'
I .
I
'
-i,-·
L._...
,1,.,.._
I- .
_.
.' .
..
..
· --- ---- :--,-.-. ---. i
1
i.:4
-r.
._
...
--
,:
T
.
.
!
--
-----
_
_
---
77_ , :.- , , i _: _1 __- .. -
....
-· :·---·
-- T- )·-·--.·
--
.
......
_
r -
·--·---- ·---
i-··f
*-·-·--·
t
7-'
1-,
_
.
.
t-
C>
r-I
.... .
__
''
-IT·--o
=:
'F
r· ----- t '---·
-e
r
6
,··-·
trr
--ir-r
t.
I
i'
i·
--
T
._.
I
i-·
-t,
·
-;-- --- - 1
I
r
·--- ·(-------i
..
-.
.
_
.....
'''
r-r-i --; Iic i-e
-- · ic- i-i
-r--+7`f-'
iii
;-L1-.
r;--.
-r--·-·-·-·--r
·-·
1---t
t, ,_-.. , _ . 1 "
t; .;i -... - ~·
,_
li----·
ccs
.
4-)
U
. it
_
_
.
.
.
FCe
4) 0
. .' . . .
----- 1-
r(
-ft
_
1:
- :-- --=:
E'':-- t:--' -.1:i~
i..
td
.t .
. :, . . a
I
- . . . :: I
t
_
-- ·--
---
,I;i
z,4-:01i
44 H4 4
·- · · t-·--·,--·-·-1-·--t--·-·-
I.
:
.
, :. . t : . .
---
-Irl
-I
. . ...
..
---I
m: - .
t . ._.
. . . -J..
.....
_ -
-A
-
. .
':
i .
_I
__I .'
4---,
,-".,
_4 yj _6 , '.
_
T't
'
*4
_
;
t
- t ·
-.. :-,JE-1 E-4 E-1 -
.~- _+_. t
.
.
·
t
n
7t-t
.7':t
; jj_
.....-r.
_
2
I..
- i
t-
;....
j
: -- --i-
-t--i ....---.
-..-------
....
t
· · · I--·--- f ----·+·I----
-
-.
, .4
.:- :_
---- . -- -''.
__ ,- ___
7- V
- -I _. .___
. . .., __". . -,, .. - . -.__
...
- . - -- V
i
b
.
-
----_
-
I,
..
.
-- , --
t---r--t-r
e;-t-t
---
:
_--
-
.
e~nE- o
-,-: :.-
--
- -
·- l--rr·-
-!.
.--
I.
I
.
- -t--·:,. - --F;i
-::E,[-}:'
CT·----
-+- -r------
-
.
-- I
_
.:
='., _
.
.
.
: :-
'O
Es
V (d XJ
go O
. . j-
.
.
_.:.
_
--- - - t - - -
:.
i
: - .- I .
+_ ..__.._
-- , _ ..
i..
.. 7.
·.
---.-.._.L_
---· -- 1.;, ._.
':-.'--1----zt
:.- -- --.- ·-,
.- . .. . .
44
_--t--
-----1·-----·
i-
---------
t 7__::_----i-_
:-: -::
'-'7
J
....! ......
_
j,
.
·
i
.
... :. ...
.
.
o
:
-.iw
.-- I
I
·
----t
. _
.-....
.
·
_
i
I
._
.
<J
.
_
_
.,i!
<
.
.
.
:
---
>
~ ~ ~i ~ ~ ~
'.'_..
.
-
---
~ ~
· ·..
T':·
.. ..
I
I .......- . ... ..
t--:-- :
t
~
-
. . .. . r - -
- -
- -
+-
---
|
~
--
I
I - ._ _ 4
. -
~
!,._---'.-'""].--;:
--
-
I
-
t
- * -
-
I :
-;11.
.I ~~~~~~~~~~
_ .
_. ._..--.- ...
- --- -.--t:-_
~
T
:-
:: ...
f- : .: i:
i------L--·--
I-·
. . ..,
A419M m
-
1I
L----. ---
.---
~
[
'~.-
~.:-...:-.._
'
i
i.:-.::.
_ I- -,-- - _
tI - -~'. ':
oo
.
--t---- -I
__
.i
_
__
m;'L~:
I_
·-
T
--
o
C>
w
V-26
is substantially greater than the lower plenum temperature.
This is
due to the periodic expansion of steam from the heated section into
the inlet section and the resulting condensation and mixing.
At heat
fluxes above 5 x 104 BTU/hr ft2, the inlet temperature appears to be
relatively constant at 190-1950 F.
However, this is based on only two
4
data points, the last being at a heat flux of 5.93 x 10
2
BTU/hr ft.
The fact that the exit fluid temperature remained at the saturation
temperature for heat fluxes beyond the CHF, added to the observation
that water was present at the upper sight flow indicator, shows that
there is entrained liquid present at the top of the test section even
beyond CHF.
Thus CHF occurs at an average exit quality of less than
1.0; and, if rewetting were possible above 7.3 x 104 BTU/hr ft2, the
water would be present to do it.
The heat transfer coefficient calculated from the temperature
data at the top of the heated section (see Table IV-4) is plotted as
a function of heat flux in Figure V-9.
(Also shown on this graph are
the heat transfer coefficients calculated from data obtained in Runs
1, 2, and 3 discussed in Sections V.A.1 and V.A.2.)
For comparison,
the heat transfer coefficient calculated at various heat fluxes using
the Jens-Lottes correlation (Equation V-8) is also shown.
Figure V-9 shows that at low heat fluxes near 1 x 104 BTU/hr ft2 ,
corresponding to the onset of subcooled boiling, the measured heat
transfer coefficient is less than predicted by the Jens-Lottes
correlation.
However, for this heat flux condition, nucleate boiling
has probably not yet become fully developed.
1.75 x 104 BTU/hr
ft2 the measured
At a heat flux of
heat transfer
coefficient
is in
very good agreement with the Jens Lottes correlation, indicating that,
for this condition, nucleate boiling is fully developed.
V-27
0
r
W
0)
a)
0
0
Cd
4J
Id
0
b
In
,.
--t-
i.
44-
i.i.
-
F---
I--
.
.:..
: .::t .
.,. ....
III
_...: -
._
:
. .
.
.:.
i.
.
I.
I
.
'. . .
.
.
_
F.::
.. I
l i~ : iii
· ''
i'
..
T--r- .. . ...
··I
'.
;,
··
-1
_L.
...
....
04)
t....
....
·
:::: :: i e:
,,..,
Ii
0O
..
..
I_
a
.-
tt· ·
t·?-l
-·; i;
i
...
rrr
.
I.
1:-;
rl I-I·rl
i,
':I
.
r-e
4
' · 1j
T'.
.
!
I..
.
-
: .'
; ,:: -~~,t I
'
..--
...
.'
'
.
..
.
i
.
'
t- -' ·
*I
I··
:: I:.
:LL
.
:.
.
'
i -·
· · t -- · ·
· ·· I..:.
;,T
',
j.
i i'
·:I
@s
1;; r.
i --
,
;· I ,
·
..
II ·
. I
· ' '
W.
_
't
. ·
'l
··:
..
-77
-I-4
IT:
· ·?
· ·· ·t
-i-:
···
·'
'
.. ~
-- C
i I
, .
:;;
l.'.
.:.
ii'
; · : I··1:
;,.
.
!i
0
oo
IV
··'
.-
{
o
· ·: t
· 1k
~·
I....
--- ·-...
.
.
....T s.
··
I.
· ·;
:
-1:I.
:1:.:-
:.!'
.
.
'. .:
····
''t
....
L,
'
····
:t-
.
rf
'
::..: ,,.
....
"
X.
.
.
.
1;:~
..
, , .. .- ,: i
!
.
.
.. .
:''
··
·
m
'··
_+__
77,
.i;!
;,'
l.
::: !: : : ....: :
I:
"-
,! _ .... _
.
...
,
:· · ·
.
.. .
i
+.
....
I;.~
L': !
4.:
··
'''
'''
: :Ii.
. !.
. ..: :
t.
':t I ·!; !'' I . 11
TI C11
.
-r,
qI
'I
i
....
.,
,...
:rt"
·- t--
1-': '
·:
...
,
'tl II
'·I-I
·i
::
|:'
on r~r. .
W
.
hf
·· ·· '·· LI'
·'
i.
· · ·- I·: L·
.-. ..
....
_T_
to
I
7::!
....
II
·i
, .
···
77,
·'
i:'
. .. .,..
ii
...
·'
:
·'
· · · lr-rr
,.|.
.. ,
.--
'''''
-':
|j
..
,.:
T.
.
.
i:-
'':'
,-l
.
1-·
.
· ''
"-·-I-·!'
.
· · · (··
:··
· ·· I
· ''
._
4 o
-r
.....-
-7.
· ' ''
''''
i
: :
·_
...:
'''
iI
·-
-tsl -
.
· '''
i i ::
'''
.......
....
P.1
.7
I
j·
i *Ur-I
fr.
,d
.
-.
.. ·. I.-.
1:;
I -
· '''
ii
····
.
,
,
i:
1'''
···
··
..
-·-+;-
····
·'
1:·
N-
. I
· ' ''
·; ·
·· ·
Z@t-
.i
r--
::i:
,. . .
-
i:
'':
OH
'
-
*
" ''
4
...
t---.
. I
...
..
... 1- ..
: :: I .-:.:
''`'
· '`'
14J
..
._
_I
' ''1: ''
::',,
.
.H
_
:...:1
.,
.
Li
>i I-
_
i
. .7
i .
. . .
'''
7Z
-.
_-
'7'
T1
._7
.
: 7
Ii-:
1'
f:
C
-77 ·
I..
·-
0o
L-:-
.....
..
L :._,m
.-
... I ''
1.._._
E.-
,
t...
1. : .
l
.
-
i-
.
.l'
.r1
.
r-l
I!,'
.
0.
Co
I-
.
0
0
eq
" -- r t
.
·: ·
r r;
I
T
TI i
.
I
!t . '
.
·
']; t
It
-
'[I
]
*
:1
:
····
-r,
-717--
i rT
.
.
.
0
_
_
_
H
r-1
ao Z-4
_
00
. . ....
_
Co
l/nfl
cO
'
' TT
I
00
.L"
0
I::
_
_
O
'44
V-28
At heat fluxes between
3 x 104 BTU/hr
ft 2 and 4 to 4.5 x 104
BTU/hr ft2, the measured heat transfer coefficient is greater than
predicted from the Jens-Lottes correlation.
But, for this range of
conditions, the heat transfer coefficient is decreasing; and, above
4.5 x 104 BTU/hr ft2 , the measured heat transfer coefficient becomes
less than predicted by the Jens Lottes correlation.
This comparison
indicates that a nucleate boiling heat transfer correlation such as
Jens-Lottes doesn't apply for flow conditions at heat fluxes above
2
3 x 104 BTU/hr ft
.
The proper correlation for this range of conditions
would probably be a two-phase convection heat transfer correlation
such as Schrock-Grossman (9).
However, for these correlations, the
heat transfer coefficient depends on flow rate and quality; and no
information regarding flow and quality was obtained for heat fluxes
above 3 x 10
4
2
BTU/hr ft.
Therefore, no comparison can be made.
Nevertheless, it is probable (on the basis of the discussion of pressure
oscillation data and observations in Section V.A.3, part C) that, as
the heat flux increases above 3 x 104 BTU/hr ft2 , the average flow
into the test section decreases and the average exit quality increases.
These effects would result in a decreasing two phase convection heat
transfer coefficient for this range of test conditions, as was observed.
At a heat flux of 7.3 x 104 BTU/hr ft2 (for which the tube wall
temperature remains above the Liedenfrost temperature) the heat
transfer coefficient at the top of the heated section is still 75 BTU/
hr ft2°F.
Assuming a mass flow rate of 2.25 x 10- 3 lbm/sec (from
Figure V-5 for a heat flux of 7.3 x 104 BTU/hr ft2 ) and an exit
quality of 1.0 (neglecting the effect of any liquid present) and using
the Dittus Boelter correlation gives 88 BTU/hr ft2°F.
Thus the
magnitude of the heat transfer coefficient beyond dryout is approximately
what would be expected as a result of convection to steam with a
V-29
quality of 1.0 and a flow rate predicted from the analysis presented
in Section V.A.1.
c.
Discussion of CHF Mechanism
The preceding results indicate that CHF was due to dryout.
However, the CHF of 6.4 x 104 BTU/hr ft2 was significantly higher than
would be predicted from a simple homogeneous flow model.
This can be
seen from Figure V-5 which shows that a stable flow condition corresponding to an exit quality of 1.0 is predicted at a heat flux 4.25 x
104 BTU/hr ft2.
However, this prediction assumes dryout does not occur
as long as any water is present; since, if it were assumed that some
of the water is entrained.inthe steam and does not help to keep the wall
wet, dryout would occur at a lower quality.
If it is assumed that
dryout occurs at an outlet quality of 0.5, for example, Figure V-5
would predict dryout at 3.5 x 104 BTU/hr ft2
The fact that dryout occurs at 6.4 x 104 BTU/hr ft2
,
rather than
4.25 x104 BTU/hr ft2 or below, is probably a result of the pressure
and.flow oscillations.
As discussed in Section V.A.3, these oscil-
lations appear to maintain an average quality at the top of the heated
section which is lower than predicted from Figure V-5.
Moreover,
even at heat fluxes above CHF, these oscillations continue to provide
enough water for periodic rewetting of the tube wall; and the Liedenfrost temperature is not exceeded until the heat flux is above
7.3 x 10
5.
BTU/hr
ft2
Transient Tests (Runs #5 and #6)
a.
Step Increase in Heat Flux to Beyond CHF (Run #5)
This test was discussed in Section IV.B.1.
The heat flux
was increased from zero to 7.3 x 104 BTU/hr ft2 using a knife switch.
The result is shown in Figure IV-6.
This Figure and the visual
observations at the sight flow indicators indicate that the equilibrium
V-30
flow condition (Run #4) was reached within a few seconds.
The equili-
brium tube wall temperature at T6 (upstream of the CHF location) was
reached in 10 seconds.
However, the equilibrium tube wall temperature
at the CHF location was not reached until about 135 seconds after the
power was turned on.
This result provides evidence that the flow oscillations corresponding to CHF would develop very quickly in a transient situation.
Moreover, the CHF condition appears to result in the same tube wall
temperatures regardless of whether it is approached slowly from lower
heat fluxes or very rapidly in a single step.
b.
Liedenfrost Temperature (Run #6)
This test was discussed in Section IV.B.2.
The heat flux
was increased to about 8 x 104 BTU/hr ft2 and the temperature was
allowed to increase to about 15470 F.
Then the power was decreased to
well below the power corresponding to CHF.
The resulting temperature
transient (Figure IV-5) shows a sharp increase in the cooldown rate
once the temperature drops below 900F.
This provides additional
evidence that the Liedenfrost temperature is about 9000 F for the steamwater system used for these tests.
B.
Analysis of LMFBR
1.
Flow-Pressure Drop Characteristics of Reactor Loop
In Section V.A.l1, an analysis was done to determine the flow-
pressure drop characteristics of the water test loop.
A similar
analysis can be done for the reactor loop shown in Figure II-la.
Therefore steady state solutions for Equation (V-2) for the reactor
loop can be obtained as described in Section V.A.l1, providing the
numerical values used for fixed parameters involving geometry and fluid
properties are those appropriate to the reactor loop.
The results of
V-31
such an analysis are shown in Figures V-10, V-ll, and V-12.
The numerical values of fixed parameters involving geometry and
fluid properties were those listed for the FTR in Tables II-1A and
II-1B.
These values were the following:
..
w
pf = 46.4
lbm/ft 3
x 1 = -0.165
Pf
= 1865
-
f = 0.0055
D = 0.128 in.
A = 0.0154 in.2
L1 = 131 in.
LH = 36 in.
L 2 = 48 in.
2
L 2 = 57 in.
The values of D, A, and L 1 were obtained from data and information
taken from Reference (9).
D and A are, respectively, the equivalent
diameter and flow area for an average subchannel of the reactor and
were obtained from Appendix I of Reference (9).
L1 was obtained from
information in Table 3.4 of Reference (9) which indicates that, for an
average assembly (Zone 1), the ratio of the rated single phase flow
pressure drop across the inlet nozzle and orifice block to the
pressure drop across the core region of the bundle is 60.6/16.7 or
3.63.
Thus:
L1 = 3.63(36) = 131 in.
i
.:
I
,!
..
-
,
4
-
_ _i
: i
.I
C&
__ I
- 7----
_.
i
I
!
~~ I
1
-
-I
- I
Li.-:
---
-
I-
H
--
t
i
i --
-
-----.
-
--- 4c- ---
----,-
.
p
I--I---
i
L
.-L1Z
ii
I
0
I
f-v
..
f
I
It
I
,-HD
i
'i:- I'
- - - :----
--- i-?-- --- -7-
-
I
--;--- ---
...
i- .
t:
:1
---t--
i-_
:.
:
F-.
I
i
.
---- C-.
-7-i
----
t--
L--
j----t--...
:.
-i
···
...
--t
--
IN
N
·,
I...
I '
7-7
777
... I
I
,
--7
,
...
·
_
-777
...
..
..
1
rL;-
,7
ii
T,
.,
L1
rs 'tY
_-1 t-
_
-
,.
1..
, .
.
.
, .
.
..
!t-
----
t--
_
1._
,....
.
,.
.
---- - 1 t---
-
t--- t-
Y
..
te
1r
--
,r,
MU
'11 -H
-4T
OD r-
1
t----
. .
i .
.
.
)
U.,
%D
t
.
rl
--1
,
,
I
.
---
'-1
--"-
-3
-- rr
-
--
t
4i:::
: : ·:
'L4
--
tt
f--
t-
t
L
I+ t
I
ti
.
__
H
:
t,-
,
i4
'- -t-7
.-
1-
7,:
i
I -- _
I
...r
L:
, i
.,c
I ::
,,4
Cui
:iL
rere
.
'1: I
71
--77
I .
U) -H
-fI
1 -1-----
--
. t,
o
ilI
II
.
.,.
Ii
i. .
7:-7
·--- T
.
T
-
C"
, -
-
iL
I .
errcl
Hn
1I
_
_
-r
111
.
I .;
...
.
-T
0
,
....
T- ""N
.
, .
-"
3m
H
I
,.
. .
I -;
L
·
4-)U2
0r,
: I
t
O
t
1 '' I
1·(
_T
t---
-f---CI
,
----
o0-.
4-JU) P
m
03
.
r)1· ·II
l. ·
I...
CN
;;
i
...
I·
-.
U)
:----i--..i
--:-
.
7;
oi
04-
.o"
i
::
1 7I
IFi;~
t---. .i
-
-7t
..
lt
fsiL
-i
i ·-
--
I··
.I
--t---
.... _1__.
i-
_·__
?5y
0o
*I..1-..
i
----i-·7--
.
o0
4
..: .T
-I.
- --1,
.
I1_
I
C-ll
-"---T---
,
I!
i
4
I
:.1
I
-.
_,
.!
Ul
'.
'~~~
T:
- -
L_ .; .
V-32
-·r ,.I.
,. ·
:. I
--
: : :r
.:
O
O
I
CN
'.
7
:..
I
-1L
.1 .
t ,(
!
,r.
i
O
O
rrfT I
:::4
-t
,
O
C)
CD,
zqj/Jsq
r
.
,~jt,
T
- lu
r;:
O
O
O
VN
(Y)
'dV
i
.1I
TO
00
00
<-Ir-
O
U EN
V-33
I
I
i
.
.1
--t
.
--
'
1
:
.i.
m
:;
i
I
I
-W
r-
'-
:-
.i
-
-
I
-
;:'
F
~0
..
ii:ii
-l
:
.
I
I-r
i.:
.
-ilK
I
__
...
1-7
_
.
I
: ::: !
..:'.
t:-·
._
i·I
...
.
- i
.
77
t
.
.
7: -7
-
...
.
-
-4jj 1L
----
. ,.·
4:-F '·
i!- @ - @
i
· ·
'Ii |
.
1
.....
4I.7
L;
..
:.
.
--
co
-1
t
I -
it'
I .
%D
,'-
.
l-:I io_' .....
-- -7 -
'''L
t
i
I
'-i
:"
--.--
..
.
.
...
..
-t:
-
tIi~-.
- --
.-.-
I~
__-
F_-
- -
----
..
ii-
-
I-
- --
.
1-+
.- 7
::i,
Hr
---I
0
'''' '''
· '"·-· II··
''
· ·· · · ·
·--··
.... : i ;
·· ·
- ·
r-
.
trr
.
b.
:
....
·
rf·trtr
""
'''
''''
'''
i-!
.
*
+
i
'
* . i
1...
-.· .·· .. ,..
:....
-·-·- · ·
···
.·.·
.....
...
. ..
..
.- :: -- ·
. .
-t
: i
I
::ml
I -
':
o.
,,
X
I
n X
HU
0
777
:iii~
:. . i
.
. 't,
r
.:
-71
...
...
. __I
it7
:
i....Il
.
-;:
, .;:
i :
,
CO
n7
,!
· · l-·lr·;
0
7'
·,·
-t-l
...
I
rT-
. ,
'"'
''''
· -·· · ·- t
.t.
-I 0
i:..rr:
m.i-
pId
f
; . · I·:·;
'II
; i!
II
I
I
.....
i_
:: : i
':':::
i:
w
: · LrYf··::
i'
· I :1
·· :
E....
.
i...
.
..
..·.
I· ' · "?~.
- 1
·."
,, ·
t
.
.
.
,i,
..
~ ,
...
.
.
.
'·1'·
~::· '
s
,
:
'
77
:i
ooI
.
..._
;'
·
t
F..;::":::
t ~III·
>v
|-
.. ....· mP, I ! .
'"
%D
...
11
1..:::'
!l2-b -
N r·
[
.. ........
Ter~
_~,4i~ d;.
I 1
,o
0D
;-! ,
=P li
A
-
_
·. ~·
16 ---
I
oLn
.: . 1,
:. ..- .t,
,|
oo
.D
__]'
.Tt:f :r
1- Irt!,
-:,. - . :, j ..
~Fm
~
fit II! .1"
, ;
4
'
7
r! 11
I
ITT![..
li
C4
.
0!
~
, t r.~
T!-W
..........
li-.1~"4~
::
11-
o
.
M
zq/gq' 'dV
r ,__' I : I ! 11
.1
oo
oci
_
,
~
.
_-
=
- -·
l
-
o0D
H-
-
]
oo
I-'-' - -1
, cnd
,
W
,_
r-4 44
}
.
-: ....
~ i ~44
~ :Iri ~~~~~~i
-':1 ';'::V..1.~':'!
1'.
: :-;'''.''.....
· · v~
· ·i ~
· · · .·~···
_'. : I
X
-l....
'
..; -:. .:_
....
.... ::::
t ,;!.....
...
'1
,:...
....
, t;'
......
' T-
Ii::
TV
;
-. > ~....
· I·0: 1 ':~ .i
r
...
i
1sill;
i:
. ':.1.: '
/
.
:: I :
· '''
· ·· '
.I:
,,.r'.........
...
.
... If:...:,: t~,, j j::
_
::; J'...::··..... -:|.-|:': ::.
::.,1:::
:,i ''t1''::'1"
': ;....... :* .: .... -: ':41';
gl|l!T
: ~; " 7':'
' '1.......
127~~~-r
7v
7r :" :. ''.
1.11
'''
·:::
:
.........
..
....im
. . ....
....
1 -· ·
·I ,' ··
:· · ·
i:
·'
· ` ''
't .....
...............
.................,m'.
..
V-34
-
i
.1.
i
-I.·---
.4.
I
1-
!
-4--
i
...
-
I-
.-..---
i
.
C .C--·I
!:i. ....
~!
! ~i
:i'..i
-t
:
---
.i-
-.-:
:
I+-
_.
:-(
i
---
:7
i
I
%o
I
.
,
-4---
·I
·:
..-.. r-. - · ·
i---
E-,
H
r-I
-Lt--
r:)f
t7
RW
17
I~~:
~
::, :.-:
ii
I.
~
4.. :
.i.t,
:.....
..:;.
-77 7
7
0
.
X
. .
I·
.1
*
HQ
r-l
·
:3
N
7
0)4.4
-,4
rzd 4.)Q
44 rl E
40.FrrO
4kr
0,r
0-
I
.rq
K-
i:!?;
.1.
:I
·. · ·
rQ)44-) 0
En =1
.~
o
717
...
t:
!!i:
:
;:::li
'
! il
0
u
$TfTT
; fI:
:I'
'''
:!: 4,
o
II
LI,
'''
0
H
'
r-4
II
'
1
(I:
I
Ii
;i
X
,'"
H.
''
--
I
(d rc
,
·. ·
o
O
0)
a)
'I,
:
n N !
1
.77-
'! '
:;r
J-
oo
04rd0)
a
-,4>
I
r-4
: :i I
...,....-
-I
I
m
C1
--
c-:::::
;:::..--!
.7
I'.
tno
r-4
M:
rD
---
·:·
o
o
i
.
rf;--
''''
0
C0
0N
oo
,-I
:I
u~
~H
* .
-7$~~~~~7
i'_
0
0
c;
! -
-$
r·
1-i.
-- -- ---
:Ii!:
CD
'* .!.4
.
--
I
iu~
i
4)
2
-
--
, . ';'
4-)
··
7-
r1l
F4
,--
.-
.. . . I . -
7l
4)
-... .. I- :-.
I
' ' ''i
--
i
I
t----I
t41
-i
j
---
I
----
~
T
.i
-, -
Ii
.4.......
,___-
r---7-1---
-- , I ,-
i
.. :
.
,.-_.........
''
I
i
i.....
C·---;
':' i. ii.
4I1
i---- - i---
l.:-,
:. .....: '::: I
_;I
.
--K-:-H
i:
!:A.[
..
---
--
---
-
iifi
--
--
,OT X
------------
M
.l/n.La
--
N
'Ib
·· . I : i
Ti--iiR
4~~
_
-
-----
--
H-
~~~~~~
0
o
V-35
Similarly, the ratio of the single phase pressure drop across the part
of the bundle associated with the fission gas plenum and the exit hardware to the pressure drop across the core region is 16.7 or 1.58.
Thus
L 2 = 1.58 x 36 = 57 in.
as listed above.
2.
Subcooled Boiling
In the LMFBR, under LOPI accident conditions subcooled boiling
would probably not occur.
This is because of the fact that, in sodium
cooled systems such as the LMFBR, a substantial amount of bulk liquid
superheat is needed before vapor generation can take place (10). The
superheat required for boiling in sodium may range as high as 5000 F;
but it is expected to be on the order of 30-500 F in a reactor
environment
3.
(11).
Bulk Boiling
For the reason given above, boiling during a LOPI accident would
probably be bulk boiling.
Therefore, a flow condition would probably
develop which is essentially the same as described in Section V.A.3
for the water tests.
Specifically, vapor generated in the core region
would probably be generated faster than it could be forced through
the top of the fuel assembly to the upper plenum.
Thus a vapor bubble
would expand downward through the fuel assembly and into the region
below the core.
However, upon contacting the subcooled liquid trying
to enter from the lower plenum, this bubble would condense and collapse,
allowing liquid to reenter the core.
An oscillatory flow condition
would'thusdevelop in which a vapor bubble alternately grows and
collapses and liquid periodically enters the core in slugs.
Once the reactor coolant pumps coast down to an extent such that
flow through core is driven only by the buoyancy force caused by the
V-36
density difference between the hot assembly and the colder assemblies
on the periphery of the core, a natural circulation loop such as shown
schematically in Figure IV-la would be established.
The flow condition
would then depend on the heat flux; and the oscillations described
above would probably result in an average mass flow rate somewhere
between the high and low quality stable flow rates predicted by
Figure V-12.
The reasoning behind this assertion is the same as given
in Section V.A.3 for the water tests.
4.
Onset of CHF
As described in Section II, the water test loop was designed
so that its flow rate-pressure drop characteristics would be similar
to the LMFBR (FTR) under both steady state and transient flow conditions.
Thus, if Q/hfg is the same for the two systems, the mass flow
rate (due to natural circulation) and exit quality should be about the
same.
Also, the rate of change of mass flow rate and quality under
oscillatory conditions should be about the same.
Therefore, for
natural circulation boiling conditions, CHF should occur at about
the same value of Q/hfg for the two systems.
But, as can be seen from Tables II-1A and II-1B, all of the
geometry and fluid property parameters of the LMFBR were not matched
exactly.
Therefore an estimate of the CHF condition for the LMFBR
can be made more accurately by using Figures V-5 and V-12, rather
than by just using the value of Q/hfg corresponding to CHF in the
water tests.
Figure V-5 shows that lowest heat flux which gives a
stable flow condition corresponding to an exit quality of 1.0 is 4.25 x
104 BTU/hr ft
2
BTU/hr ft
.
.
The corresponding heat flux for the LMFBR is 4.0 x 104
Using the ratio of these two heat flux values as a scale
factor and multiplying by the CHF of 6.4 x 104 BTU/hr ft2 observed in
the water tests then gives
for the LMFBR.
6 x
104 BTU/hr ft2 as the predicted CHF
V-37
If it is assumed (as discussed in Section II.A) that the CHF
mechanism in the LMFBR under LOPI accident conditions is dryout and
that non-uniform heat flux effects would not be of major importance,
the average fuel assembly power per subchannel corresponding to CHF
would be of more interest than the heat flux.
The average subchannel
power for a LMFBR (FTR) fuel assembly with an average heat flux equal
to the CHF is given by the following equation:
Qcritical
(CHF) (dLH) (N)
3413
(V-9)
where
d is the outside diameter of
the fuel rod cladding
N is the number of fuel rods
per assembly
Thus (using data and information from Reference [9]):
Q.t
critical
-
(6 x104 ) (r) (.23) (36) (217)
(144)(3413)
690
kw
or
Qc
l =
(690)
critical
(217) (3)
1.06 kw/ft
For comparison with this result, the average linear power for the
LMFBR (FTR) hot assembly during normal operation (initial condition for
the LOPI accident), according to Reference (9), would be approximately:
(7.3) (1.4)
=
10.2 kw/ft
or, if it is assumed that the heat flux at the time boiling starts
during
a LOPI accident
is 25 to 50 percent
of its initial value
(as
indicated by the calculations described in Section I.A), the equivalent
linear power at that time would be:
(.25 to .5) (10.2) = 2.5'5to 5.1 kw/ft
V-38
On the basis of this comparison, the results of the water tests
indicate that CHF would occur in the LMFBR (FTR) hot assembly
at the time boiling begins during a LOPI accident, if the only flow
is due to natural circulation.
But, it should be recognized that the
water test results and therefore this conclusion are probably
conservative (pessimistic) for the following reasons:
1)
The results of the water tests indicate that when CHF occurs
there is still a substantial amount of entrained liquid
present at the CHF location. But the fact that this amount
of liquid could no longer keep the heated surface wet at
the CHF location in the water tests does not mean it would
not do so in the reactor under similar conditions. This is
because the surface tension for water is substantially less
than for sodium. Therefore, in the reactor, the amount of
entrainment should be less; and the critical quality (and
CHF) would be higher than indicated by the tests.
2)
The fact that the flow is oscillating when CHF occurs
indicates that the film flow rate at the CHF location could
be ery small for short periods of time. Under such
conditions, the CHF would depend on the conductivity of the
liquid. Specifically, it would be expected that for similar time periods between arrival of slugs of liquid from
the lower plenum, the heat flux required to disrupt the
film would be less for a liquid of lower conductivity.
Therefore, since sodium has a substantially higher conductivity than water, a higher CHF would be expected, other
conditions being the same.
3)
Calculational results discussed in Section II.A indicate
that the pump induced flow through the reactor core at the
time boiling is initiated would be 20 to 30 percent of the
flow during normal operation. Therefore, even accounting
for the fact that the increased pressure drop in the hot
assembly would tend to divert flow, it is likely that the
flow would be significantly above that due to natural
circulation. This additional flow would also help to
increase the CHF above that indicated by the tests.
4)
It has been suggested (2) that, because of fission gas
pressure, the fuel rod clad would swell as it gets hot
during a LOPI transient. If this is the case the gap
conductance would decrease and the rate stored heat is
transferred from the fuel would decrease. This would
result in a lower reactor heat flux at the time boiling
begins than assumed in the above comparison.
V-39
5.
Beyond CHF
The results of the water tests indicated that, until the heat
flux was increased significantly above the CHF (7.3 x 104 BTU/hr ft2
compared to CHF of 6.4 x 104 BTU/hr ft2 ) periodic rewetting kept
the maximum tube wall temperature below the Liedenfrost temperature.
Similar effects could occur in the LMFBR.
In addition, because of
the lower surface tension. (better wetting characteristics) and
higher thermal conductivity of sodium as compared to water, post
CHF heat transfer in the LMFBR could be even better than observed in
the water tests.
Also,as the· clad temperature rises during a
temperature excursion the gap conductance effect could become even
more important.
On the other hand, if the CHF does occur at higher
quality for the reasons given above, there may not be much liquid
available for rewetting beyond CHF.
Also, since the saturation
temperature for sodium is 16700 F compared to 2120 F for water, the
initial temperature for the periodic temperature excursions would
be higher in the LMFBR.
And, the difference between the dimensions
of the electrically heated tube and the fuel clad combined with the
higher CHF would result in a dT/dt for the reactor about 6 times that
observed in the tests.
Thus the amount of time available for
rewetting before the Liedenfrost temperature is exceeded (or melting
occurs) would be very short.
The overall conclusion to be drawn
from these positive and negative factors is that post-CHF heat
transfer in the LMFBR could be better or worse than observed in the
water tests.
More prototypical tests with sodium would be needed
to determine which it is.
VI-1
VI.
A.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
As stated in Section I.B, it was expected that data and informa-
tion obtained from the tests described in this report would help to
answer
several
questions concerning the nature and effect of
natural circulation flow oscillations on post-voiding heat transfer
under conditions similar to those predicted to exist during an
LMFBR LOPI accident.
Therefore, it is appropriate to conclude this
report by summarizing some of the principal results and conclusions
from these tests within a framework provided by these questions.
What types of oscillations occur? What appears to be the
cause of these oscillations? How do they affect postvoiding, pre-CHF heat transfer?
For subcooled flow boiling, both pressure oscillations and
oscillations of the heated surface temperature were observed; but the
pressure oscillations were not observed continuously (Sections IV.A.1
and IV.A.2).
At a heat flux of about 1 x 104 BTU/hr ft2
(corresponding
approximately to the onset of subcooled boiling) the time interval
between appearance of the pressure oscillationswas about 45 seconds;
but as the heat flux/flow condition approached bulk boiling, this
time interval decreased.
At a heat flux of 1 x 104 BTU/hr ft2
the
period of the pressure oscillations was less than 1 second; but as
the heat flux/flow condition approached bulk boiling, the period
increased.
The period of the temperature oscillations was approxi-
mately the same as the time interval between appearance of the pressure
oscillations.
VI-2
The pressure oscillations were probably due to vapor bubble
formation and collapse associated with the subcooled boiling process.
The periodic appearance of the pressure oscillations at the onset of
subcooled boiling was probably due to a periodic change in the heat
transfer process at the top of the heated section from single phase
convection to nucleate boiling (Section V.A.2.b).
Calculations
indicate that this change would result in an increased flow (Section
V.A.1).
After a few seconds this increased flow, combined with the
improved heat transfer would cause a decrease in the heated surface
temperature.
Then, once the surface temperature decreased below that
needed to maintain nucleate boiling, boiling would stop and the
heat transfer mechanism would revert back to single phase convection.
Also, the flow would decrease.
This change then results in a gradual
increase in heated surface temperature back to the temperature
required for onset of nucleate boiling and the cycle would repeat.
As the heat flux/flow condition approaches bulk boiling the time
period required for this cycle of events would decrease, as was
observed.
For bulk boiling conditions, at a heat flux of 3.83 x 10
hr ft2 , pressure oscillations were observed continuously.
BTU/
However,
the heated surface temperatures were relatively steady (Section IV.A.3).
The period of the pressure oscillations was 1- 2 seconds.
The pressure oscillations observed for bulk boiling were similar
to those observed for subcooled boiling and probably also relate to
vapor (bubble)formation and collapse (Section V.A.3c).
Calculations
indicate that, for a given heat flux in the bulk boiling range,there
are two stable flow conditions (Section V.A.1).
One of these is a
high flow, low quality condition and the other is a low flow, high
quality condition.
But, the high flow low quality condition tends to
VI-3
be unstable; since, only a relatively small, momentary decrease in
flow would create an unstable situation resulting in a further decrease
in flow.
As a result, the rate of vapor generation would increase
and the quality would increase.
However, observations indicate that
a condition quickly develops where the rate of vapor generation is
greater than the rate at which it can flow out the top of the heated
section.
Thus the pressure builds up and the excess vapor pushes
downward through the heated section.
At the same time, the liquid
flow into the test section decreases and the void fraction within
the test section increases.
Eventually, enough of the test section
is voided so that the steam being generated can flow out the top of
the heated section as fast as it is being generated.
However, this
flow condition is not in thermal equilibrium in the upstream half of
the test section due to the presence of a substantial amount of
subcooled water.
As a result the steam in this part of the test
section begins to condense and the water flow into the test section
increases, causing still further condensation
and a return toward
the original high flow, lower void fraction condition from which the
transient initially started.
Then, since this flow condition tends
to be unstable the sequence begins again.
Under what conditions does CHF occur? What is the mechanism?
What is the role of the observed oscillations? How is rewetting
and post-CHF heat transfer related to the oscillations? How
does the power corresponding to CHF compare to the power it takes
to completely vaporize a steady homogeneous flow driven by the
hydrostatic pressure difference between the inlet and outlet of
the test section (or the appropriate length)?
As the CHF condition was approached the average water temperatures
entering the heated section increased to a temperature well above the
liquid temperature in the lower plenum.
This was due to the observed
periodic downward expansion of vapor from the heated section into the
VI-4
inlet section, and the resulting condensation and mixing (Section
IV.A.4).
Thus the average quality of the vapor-liquid mixture
leaving the top of the heated section also increased.
The flow regime
appeared to be annular and the film flow rate at the top of the heated
section was probably oscillating with time as a result of the pressure
and flow oscillations.
CHF was observed at a heat flux of 6.4 x 10
BTU/hr ft 2
It
occurred at the top of the heated section; and the mechanism was
probably due to dryout of the liquid film during a pressure oscillation
when vapor was expanding downward through the test section.
However,
rewetting occurred after a few seconds, apparently because of reentry
of a slug of liquid into the test section as the vapor bubble
collapsed at the other end of a pressure oscillation.
occurred again and the cycle repeated.
Then CHF
As the heat flux was increased
the maximum surface temperature during each oscillation increased;
until, at a heat flux of 7.15 x 104 BTU/hr ft2
,
the maximum temperature
exceeded 9000 F and could no longer be rewetted.
Calculation based on a homogeneous, steady flow model indicated
that the heat flux required to completely vaporize a flow driven only
by the hydrostatic pressure difference between the inlet and outlet
of the test section is 4.25x104
BTU/hr ft2 (Section V.A.1).
The
test results as stated above, indicate that the CHF is 6.4 x 104
BTU/hr ft2 .
Moreover, even at this heat flux, liquid was observed
in the flow stream downstream of the CHF location (Section IV.A.4).
Thus the oscillating flow condition observed in the tests is able to
maintain the exit quality below the CHF quality at a substantially
higher heat flux than predicted from a homogeneous, steady flow
model.
VI-5
To what extent are the answers to the previous questions
applicable to the LMFBR during the first few seconds of a
LOPI accident?
In the LMFBR, subcooled boiling would probably not occur.
This is because of the fact that, in sodium cooled systems such as
the LMFBR, a substantial amount of bulk liquid superheat is needed
before vapor generation can take place (10).
The superheat required
for boiling in sodium may range as high as 500°F; but it is expected
to be on the order of 30- 500 F in a reactor environment (11).
There-
fore, the first boiling during a LOPI accident would probably be
bulk boiling; and a flow.condition would probably develop similar to
that observed in the water tests.
Specifically, vapor generated in
the core region would probably be generated faster than it could be
forced through the top of the fuel assembly to the upper plenum.
Thus a vapor bubble would expand downward through the fuel assembly
and into the region below the core.
However, upon contacting the
subcooled liquid trying to enter from the lower plenum, this bubble
would condense and collapse, allowing liquid to reenter the core.
An
oscillatory flow condition would thus develop in which a vapor bubble
alternately grows and collapses and liquid periodically enters the
core in slugs.
Once the reactor coolant pumps coast down to an extent such that
flow through core is driven only by the buoyancy force caused by the
density difference between the hot assembly and the colder assemblies
on the periphery of the core, a natural circulation loop such as shown
schematically in Figure IV-la would be established.
The flow condi-
tion would then depend on the heat flux.
The water test loop was designed (Section II) so that its flow
rate-pressure drop characteristics would be similar to the LMFBR (FTR)
VI-6
under both steady state and transient flow conditions.
Thus, if
Q/hfg is the same for the two systems, the mass flow rate (due to
natural circulation) and exit quality should be about the same.
Also,
the rate of change of mass flow rate and quality under oscillatory
conditions should be about the same.
Therefore, for natural circula-
tion boiling conditions, CHF should occur at about the same value of
Q/hfg for the two systems.
But, as can be seen from Tables II-1A and II-1B, all of the
geometry and fluid property parameters of the LMFBR were not matched
exactly.
Therefore, analysis results based on a homogeneous flow
model (Sections V.A.1 and V.B.1) were used to obtain a scale factor
(Section V.B.4).
Multiplying this factor times the CHF of 6.4 x 104
BTU/hr ft2 observed in the water tests then gives
6 x 104 BTU/hr ft2
as the predicted CHF for the LMFBR.
If it is assumed
(as discussed
in Section
II.A) that the CHF
mechanism in the LMFBR under LOPI accident conditions is dryout and
that non-uniform heat flux effects would not be of major importance,
the average linear power of the hot fuel assembly corresponding to the
CHF would be of more interest than the heat flux.
This critical linear
power is 1.06 kw/ft, which compares to an estimated 2.55 to 5.1 kw/ft
being transferred to the coolant at the time boiling begins (Section
V.B.4).
On the basis of this comparison, the results of the water tests
indicate that CHF would occur in the LMFBR (FTR) hot assembly
at the time boiling begins during a LOPI accident, if the only flow is
due to natural circulation.
But, it should be recognized that the
water test results and therefore this conclusion areprobably conservative for the following reasons.
VI-7
1)
The results of the water tests indicate that when CHF
occurs there is still a substantial amount of entrained
liquid present at the CHF location. But the fact that
this amount of liquid could no longer keep the heated
surface wet at the CHF location in the water tests does
not mean it would not do so in the reactor under similar
conditions. This is because the surface tension for water
is substantially less than for sodium. Therefore, in the
reactor, the amount of entrainment should be less; and the
critical quality (and CHF) would be higher than indicated
by the tests.
2)
The fact that the flow is oscillating when CHF occurs
indicates that the film flow rate at the CHF location could
be very small for short periods of time. Under such
conditions, the CHF would depend on the conductivity of the
liquid. Specifically, it would be expected that for
similar time periods between arrival of slugs of liquid
from the lower plenum, the heat flux required to disrupt
the film would be less for a liquid of lower conductivity.
Therefore, since sodium has a substantially higher conductivity than water, a higher CHF would be expected, other
conditions being the'same.
3)
Calculational results discussed in Section II.A indicate
that the pump induced flow through the reactor core at the
time boiling is initiated would be 20 to 30 percent of the
flow during normal operation. Therefore, even accounting
for the fact that the increased pressure drop in the hot
assembly would tend to divert flow, it is likely that the
flow would be significantly above that due to natural
circulation. This additional flow would also help to
increase the CHF above that indicated by the tests.
4)
It has been suggested (2) that, because of fission gas
pressure, the fuel rod clad would swell as it gets hot during
a LOPI transient. If this is the case the gap conductance
would decrease and the rate stored heat is transferred from
the fuel would decrease. This would result in a lower
reactor heat flux at the time boiling begins than assumed
in the above comparison.
The results of the water tests indicated that, until the heat
flux was increased significantly above the CHF (7.15x 104 BTU/hr ft2
compared to CHF of 6.4 x 10
4
2
BTU/hr ft ) periodic rewetting kept the
maximum tube wall temperature below the Liedenfrost temperature.
Similar effects could occur in the LMFBR.
In addition, because of the
lower surface tension (better wetting characteristics) and higher
thermal conductivity of sodium as compared to water, post-CHF heat
transfer in the LMFBR could be even better than observed in the water
VI-8
tests.
Also as the clad temperature rises during a temperature
excursion the gap conductance effect could become even more important.
On the other hand, if the CHF does occur at higher quality for the
reasons given above, there may not be much liquid available for
rewetting beyond CHF.
sodium is 1670F
Also, since the saturation temperature for
compared to 2120 F for water, the initial temperature
for the periodic temperature excursions would be higher in the LMFBR.
And, the difference between the dimensions of the electrically heated
tube and the fuel clad combined with the higher CHF would result in
a dT/dt for the reactor about 6 times that observed in the tests.
Thus the amount of time available for rewetting before the Liedenfrost
temperature is exceeded (or melting occurs) would be very short.
The
overall conclusion to be drawn from these positive and negative
factors is that post-CHF heat transfer in the LMFBR could be better or
worse than observed in the water tests.
More prototypical tests with
sodium would be needed to determine which it is.
B.
Recommendations
Recommendations for further work based on the results of the
tests and analyses described in this report are the following:
1)
Experimental and analytical work should continue using the
low-pressure water loop used for the tests described in
this report. Additional experiments should focus on preCHF conditions. More detailed measurements should be made
relating to pressure oscillations near CHF. In addition,
flow measurements should be made in order to verify some
of the conclusions arrived at in this study. Further
experiments might also include modifications of test
section geometry to allow better visualization of flow
conditions near the CHF location. A transient experiment
might also be run to simulate the LOPI flow transient and
the effect of pump induced flow remaining at the time
boiling starts. Analytical work should include development
of a more detailed model of the oscillating flow conditions
leading to CHF. This model should include transient effects,
slip flow and non-equilibrium effects.
VI-9
2)
Similar tests should be run with sodium. Initially, it is
suggested that such tests be done using a simple loop
geometry similar to the water test loop. Measurements
should be the same as in the water tests, except that
measurement of test section flow should also be included.
Also, the focus should be on heat flux conditions near CHF.
Both steady state and transient tests (of the type included
in the water tests)- should be done. The results should be
compared with the water tests and the analysis in Section
V.B of this report (or some improvement on this analysis).
Once the tests with the simple geometry are completed, more
prototypical tests should-be conducted using rod bundle
geometry.
I
REFERENCES
1.
Driscoll, M., P. M. Magee, and Y. S. Tang, Unpublished papers
and analyses prepared for ERDA LMFBR Loss of Pipe Integrity
Working Group, February - August, 1975.
2.
Griffith, P., "An Overview of LMFBR Voiding," Unpublished paper
prepared for ERDA LMFBR Loss of Pipe Integrity Working Group,
March, 1975.
3.
Blaisdell,
J. A., L. E. Hochreiter,
and J. P. Waring,
"PWR
FLECHT-SET Phase A Report," WCAP-8239, December, 1973.
4.
Bonilla, C. F., "Nuclear Engineering," McGraw Hill, 1957,
Chapter
5.
8.
Bouve, J. A., A. E. Bergles,
and L. S. Tong,
"Review of Two
Phase Flow Instabiltiy," ASME Paper 71-HT-42, Paper presented
at the ASME-AIChE Heat Transfer Conference held in Tulsa,
Oklahoma, August 15-18, 1971.
6.
Bergles, A. E., and W. M. Rohsenow, "The Determination of Forced
Convection Surface Boiling Heat Transfer," ASME Paper 63-HT-22.
Paper presented at the 6th ASME-AIChe Heat Transfer Conference
held in Boston, August 11-14, 1963.
7.
Bonilla, C. F., "Nuclear Engineering," McGraw Hill, 1957,
Chapter
9.
8.
Schrock, V.E. and L. M. Grossman, "Forced Convection Boiling
Studies," Final Report on Forced Convection Vaporization Project,
TID-14632, 1959.
9.
Calamai, G. J. et al., "Steady State Thermal and Hydraulic
Characteristics of the FFTF Fuel Assemblies," FRT-1582,
June 1974.
10.
Collier, J. G., "Boiling of Liquid Alkali Metals," Chemical Process
Engineering Heat Transfer Survey, 1968.
11.
Graham, J., "Fast Reactor Safety," Academic Press, 1971, p. 26.
12.
McAdams, W. H., Heat Transmission, McGraw Hill, Third Edition,
1954, p. 19, Equation
(2-14d).
NOMENCLATURE
A
Cross sectional flow area of tube or average reactor
fuel assembly subcahnnel, ft2 .
Cf
Specific heat of saturated liquid, BTU/lbm°F.
Cs
Specific heat of stainless steel, BTU/lbmOF.
CHF
Critical heat flux, BTU/hr ft.
D
Diameter of tube or equivalent diameter of average
reactor fuel assembly subchannel, ft.
d
Outside diameter of reactor fuel rod clad, ft.
F1
Quantity in Equation V-7 defined as fraction of one
cycle of temperature oscillation for which flow is
single phase, dimensionless.
F2
Quantity in Equation V-7 defined as fraction of one
cycle of temperature oscillation for subcooled boiling
occurs, dimensionless.
f
Fanning friction factor, dimensionless.
g
Gravitational acceleration, 32.2 ft/sec .
gc
Dimensional constant, 32.2 lbmft/lbfsec .
h
Enthalpy of liquid or liquid-vapor mixture, BTU/lb.
hfg
Enthalpy of vaporization, BTU/lbm .
h
Heat transfer coefficient corresponding to average test
section flow, BTU/hr ft F.
i12
Heat transfer coefficient at top of test section heated
length, as calculated from Equation (III- 6), BTU/hr ft 2
2
2
2
OF.
J
Mechanical equivalent of heat, 778 ft lbf/BTU.
K1
Friction coefficient associated with flow area contraction
at test section inlet, dimensionless.
K2
Friction coefficient associated with flow area expansion
at test section outlet, dimensionless.
kf
Thermal conductivity of saturated liquid, BTU/hr ft°F.
ks
Thermal conductivity of stainless steel, BTU/hr ft°F.
L
Total length of vertical tube test section or reactor
fuel assembly, ft.
L1
Length of unheated inlet section of the test section or
reactor fuel assembly, ft.
L1
Equivalent length of the unheated inlet section of the
test section or reactor fuel assembly, including the
effect of the inlet contraction and orifice, ft.
L1¢
- Length of the single phase region within the test
section or reactor fuel assembly, ft.
Equivalent length of the single phase region of the test
section or reactor fuel assembly, including the effect
of the inlet contraction and orifice, ft.
LH
Length of the heated section of the test section or
reactor fuel assembly, ft.
L2
Length of the unheated outlet section of the test section
or reactor fuel assembly, ft.
L2
Equivalent length of the unheated outlet section of the
test section or reactor fuel assembly, including the
effect of the outlet expansion, ft.
L20
Length of the two-phase region of the test section or
reactor fuel assembly, ft.
L2
Equivalent length of the two-phase region of the test
section or reactor fuel assembly, ft.
LB
Boiling length within the test section or reactor fuel
assembly, as defined by Equation (II-14), ft.
N
Number of fuel rods per reactor fuel assembly,
dimensionless.
P
Static pressure, psia.
AP
Pressure drop, lb/ft2 .
Pl'P2 and P 3
Pressures at various locations in the test loop (see
Figure II-9), psig.
Prf
Prandtl number of saturated liquid,
less.
Q
Power of test section or average reactor fuel assembly
subchannel, BTU/hr or kw.
critical
dcritical
fCf/kf, dimension-
Power of test section or average reactor fuel assembly
corresponding to CHF, BTU/hr or kw.
Linear power of average reactor subchannel corresponding
to CHF, kw/ft.
q"
Average heat flux to test section2or reactor fuel
assembly heated length, BTU/hr ft.
q" (z)
Heat flux at a specific distance, z, from the inlet of
the test section or reactor fuel assembly, BTU/hr ft2 .
Heat flux required for onset of nucleate boiling at
2
(ATat)
sat ONB according to Equation (V-4), BTU/hr ft .
Average two-phase friction multiplier along the twophase length of the test section or reactor fuel
assembly, defined in relation to Equation (II-8),
dimensionless.
R1
Inside radius of vertical tube test section, ft.
R2
Outside radius of vertical tube test section, ft.
Ref
Reynolds number,
T 1 through
Temperatures at various locations in the test loop (see
15
Figure
II-9),
4 W/f7Dpf, dimensionless.
OF.
T.
1
Temperature of the inside surface of the vertical tube
test section, F.
T
0
Temperature of the outside surface of the vertical tube
test section, OF.
Average temperature of stainless steel tube wall or
fuel rod clad, F.
T
sat
Liquid saturation temperature, OF.
ATsat
Difference between temperature of heated surface and
liquid saturation temperature, F.
(ATsat)ONB
ATsat required for the onset of nucleate boiling at
qONB according
to Equation
(V-4),
F.
u
Internal energy of liquid or liquid-vapor mixture,
BTU/lbm .
VL
Velocity of single phase liquid, ft/sec.
Vm
Velocity of liquid-vapor mixture in homogeneous flow,
vf
Specific volume of saturated liquid, ft3 /lbm
v
Specific volume of saturated vapor, ft3 /lbm.
g
Vfg
v
m
as defined in relation
(II-3), ft/sec.
Difference, VgVf
to Equations
(II-1),
(II-2) and
ft3 /lbm
Specific volume of liquid-vapor mixture in homogeneous
flow, lbm/ft3.
W
Mass flow rate of liquid or liquid-vapor mixture,
lbm/hr.
W
Average mass flow rate of liquid or liquid-vapor mixture,
lbm/hr.
x
Flowing or thermodynamic equilibrium quality, dimensionless.
Quality of liquid in lower plenum of test loop or
f
Xout
X2
Quality of liquid-vapor mixture leaving heated section
of test section or reactor fuel assembly, dimensionless.
Quality of liquid in upper plenum of test loop or
reactor
z
hfg
C ' (T at
hfg
2)
dimensionless.
Distance from inlet of test section or reactor fuel
assembly,
ft.
Greek Letters
6
Thickness of test section tube wall or reactor cladding,
ft.
Pf
Viscosity of saturated liquid, lbm/ft hr.
Constant, 3.14.
Pf
Pg
PL
Pm
A
Pm
Density of saturated liquid, lbm/ft3
Density of saturated vapor, lbm/ft3.
Density of subcooled liquid, lbm/ft.
Density of liquid-vapor mixture in homogeneous flow,
lbm/ft .
Average density of liquid-vapor mixture along the twophase length of the test section or reactor fuel
assembly, defined in relation to Equation (II-8),
dimensionless.
Ps
Density of stainless steel, lbm/ft3 .
of
Liquid surface tension, lbf/ft.
T
2
Wall shear stress, lbf/ft
Dimensionless quantity, xou Pf defined in relation to
Equation (V-2).
out Pg'