NAME: KATLEGO GAOALAFE
STUDENT ID: 202000271
LAB SLOT: MONDAY 2-4
MMB323 LAB 1 REPORT – DERTERMINATION OF DRYNESS FRACTION OF THE STEAM SUPPLY
ABSTRACT
Steam calorimeters are commonly used to determine the quality of steam in process industries, power
plants and other industries. Performance of steam processes depend on the quality of. Separating or
throttling or combined separating and throttling calorimeters are being used for this purpose. This
experiment a combined calorimeter was used to determine the dryness fraction of steam. Finding of the
separating and throttling calorimeters individually and then multiplying them together helped find the
final value of steam. Experimental errors were found during the process however the objectives of the
experiment were completed.
INTRODUCTION
This experiment was conducted to determine the dryness fraction of the steam supply using the
combined separating and throttling calorimeters. The following shall fully explain the processes
undergone.
AIMS
The aims of the experiments is to find out:


Measurement of Dryness fraction of steam by using :
1. The separating calorimeter
2. The throttling calorimeter
3. Both separating and throttling calorimeter together
Understanding various methods of measurement of Dryness fraction
THEORY
1. Separating calorimeter:
Separating calorimeter is used when the steam is very wet, the quality of wet steam is shown by its
dryness fraction. When the dryness fraction, pressure and temperature of the steam are known, then
the state of wet steam is fully defined.
Figure 1: Separating calorimeter
The steam is collected out of the main steam supply and enters the separator from the top. The steam is
forced to make a sharp turn when it hits the perforated cup (or any other mechanism that produces the
same effect). This results in a vortex motion in the steam, and water separates out by the centrifugal
action. The droplets then remain inside the separator and are collected at the bottom, where the level
can be recorded from the water glass. The dry steam will pass out of the calorimeter into a small
condenser for the collection of the condensate. However, not all the water droplets remain in the
collector tank. Some water droplets pass through to the condenser, and hence this calorimeter only
gives a close approximation of the dryness fraction of the steam. From the results obtained from the
two collectors, the dryness fraction may then be found from
Dryness fraction =
This can be expressed as:
x=
M is the mass of dry steam and m is the mass of suspended water separated in the
calorimeter in the same time.
2. Throttling calorimeter:
It is used when steam is nearly dry. This calorimeter is operated by first opening the stop valve
completely so that the steam is not partially throttled as it flows through the apparatus for a while to
allow the pressure and temperature to stabilize. If the pressure is very near to atmospheric pressure,
the saturation should be 100°C, it may be assumed that the steam is superheated. When the conditions
have become steady, the gauge pressure before throttling is read from the pressure gauge. After
throttling, the temperature and gauge pressure are read from the thermometer and manometer. The
barometric pressure is also recorded.
From the equation h1=h2 .We have:
ℎ2 p1=hsup at p2
ℎ𝑓1 + 𝑋 ∗ ℎ𝑓𝑔1 = ℎ𝑔2 + 𝐶𝑝 (𝑇𝑠𝑢𝑝 − 𝑇𝑠𝑎𝑡 )
𝑋=
Figure 2: Throttling calorimeter
ℎ𝑔2 + 𝐶𝑝 (𝑇𝑠𝑢𝑝 − 𝑇𝑠𝑎𝑡 ) − ℎ𝑓1
ℎ𝑓𝑔1
3. Separating and throttling calorimeter:
If the steam dryness fraction is to be determined is very wet then throttling to atmospheric pressure
may not be suitable to ensure superheated steam at exit. In this case it is necessary to dry the steam
partially, before throttling. Done by passing the steam from the main through a separating calorimeter
as shown in figure 3. The steam changes direction suddenly, and the water being denser than the dry
steam is separated out. The quantity of water which is separated out (mw) is measured at the separator,
the steam remaining which now has a higher dryness fraction, is passed through the throttling
calorimeter. With the combined separating and throttling calorimeter it is necessary to condense the
steam after throttling and measure the amount of condensate (ms). If a throttling calorimeter only is
sufficient, there is no need to measure condensate, the pressure and temperature measurements at exit
being sufficient.
Figure 3: Separating and throttling calorimeter
APPARATUS USED




Mini steam power pant
Separating calorimeter
Throttling calorimeter
Measuring cylinder
PROCEDURE
The isolating valves (V1) were checked to see if it was closed for both the separating and throttling
calorimeter. Steam flow along the steam header was arranged furthermore the steam trap pipe in the
closure unit, P7682 was not isolated. Moreover the steam header was allowed to reach full working
pressure and temperature. The cooling water supply valve (V4) was then turned on, furthermore the
condensate collecting valves were placed under the condenser outlet. Afterwards the drain valves (V2)
and the small valves (V3) were closed and the digital manometer of throttling calorimeter was isolated.
Moreover water flowing through the condenser was checked to ensure it being sufficient to condense
the steam. The steam valves (V1) were then open allowing steam to flow, followed by the partial
opening of the drain valve (V2) the steam flowed through the separating chamber to warm up the
system. During this process the drain vessel collects water. Afterwards the drain valve (V2) were closed
followed by the opening of valve (V3) to the manometer. The separating condensate level was allowed
to build up and can be seen in the calorimeter level tube. Furthermore the main condensate collecting
vessel was drained and put back. The following measurements were then taken, the initial value of fluid
level in the separating calorimeter, the initial value of the condensate level in the collecting vessel, the
steam pressure, the steam pressure after throttling and the main steam temperature. The values of the
last four quantities were recorded every 10 minutes for about six times during the experiment, followed
by the recording of the barometric pressure. Furthermore a reasonable amount of condensate was
allowed to collect then measured and the value of fluid level in the separating calorimeter was also
noted .Afterwards the steam supply (V1) was turned off once the experiment ended, followed by the
closing of valve (V3) to isolate the manometer. Moreover everything was allowed to cool and the
condenser cooling water valve (V4) was turned off .Draining of the separating calorimeter and the
condensate collecting vessel was done.
RESULTS
Table 1: Showing results found in the experiment
DATA
Steam pressure in
P1(bar)
Temperature in main
before throttling
T1(deg)
Steam pressure after
throttling P2(bar)
Temperature in main
after throttling
T2(deg)
1
7
2
6.5
3
7
4
7
5
6.75
6
6.5
Average
6.792
172
170
172
172
172
171
171.5
73
72
71
72
72
72
72
116
120
121
121
122
124
121
Table 2:Showing the values of separated water, condensate and the barometric pressure
DATA
Quantity of separated water(ml)
Quantity of condensate water(ml)
Barometric pressure(bar)
VALUE
415
11590
1.5
Figure 4: Separating and throttling calorimeter
Calculating the dryness fraction of the steam supply by using
a) Separating calorimeter:
𝑚𝑠
𝑚𝑠 + 𝑚𝑤
11590
=
11590 + 415
= 𝟎. 𝟗𝟔𝟓
𝑥1 =
b) Throttling calorimeter
ℎ𝑔 + 𝐶𝑝𝑠 (𝑇𝑠𝑢𝑝 − 𝑇𝑠𝑎𝑡 ) − ℎ𝑓
ℎ𝑓𝑔
(ℎ2− ℎ1 )(𝑝 − 𝑝1 )
ℎ𝑔 =
𝑝1 − 𝑝2
(2722 − 2766)(72 − 70)
=
+ 2722
75 − 70
= 2754.4 𝑘𝐽/𝑘𝑔
(ℎ2− ℎ1 )(𝑝 − 𝑝1 )
ℎ𝑓 =
𝑝1 − 𝑝2
(697 − 670)(6.792 − 6)
=
+ 691.384
7−6
691.384𝑘𝐽
=
𝑘𝑔
(ℎ2− ℎ1 )(𝑝 − 𝑝1 )
ℎ𝑓𝑔 =
𝑝1 − 𝑝2
𝑥2 =
(2067 − 2087)(6.792 − 6)
+ 2087
7−6
𝑇2 − 𝑇1
𝑇𝑠𝑎𝑡 =
× (𝑝 − 𝑝1 ) + 𝑇1
𝑝2 − 𝑝1
290.5 − 285.8
=
× (72 − 70) + 285.8
75 − 70
= 𝟐𝟖𝟕. 𝟓℃
=
Therefore:
2754.4 + 2.1(121 − 287.5) − 691.384
2075.16
= 0.256
c) Combined throttling and separating calorimeter
𝑋 = 𝑥1 × 𝑥2
= 0.826 × 0.996
= 𝟎. 𝟖𝟐𝟐
𝑥2 =
DISCUSSION
The dryness fraction of the combined separating and throttling calorimeter was calculated using the
individual dryness fractions from separating calorimeter is 0.996 followed by 0.826 from throttling and
then multiplying them together, the value obtained was 0.822. This shows that the steam was wet but
because the value is close to 1, this means it contained few particles of water. The value of the dryness
fraction calculated with the throttling calorimeter is not realistic as when we compare it with that of a
similar experiment conducted by,( Sagar G. Mushan et al, 2020), the value is always above 0.95. this
error may have been caused by experimental errors including but not limited to: incorrect calibration of
the steam calorimetry, incorrect reading of the temperature and pressure on the system and human
error when taking the water level readings with respect to the sight glass reference work. it would be
recommended to maintain the laboratory apparatus to reduce risk of more experimental error.
CONCLUSION
In conclusion, the purpose of this experiment was to estimate the quality of steam using a combined
throttling and separating calorimeter and the objective of the experiment was completed. The dryness
fraction of steam at the separating and throttling calorimeter was 0.996 and 0.822 respectively. when
combined the overall value was 0.822.
REFERENCES
5.2 calorimetry - chemistry 2E. OpenStax. (n.d.). Retrieved March 17, 2023, from
https://openstax.org/books/chemistry-2e/pages/5-2-calorimetry
Moran, M. J., & Shapiro, H. N. (2004). Fundamentals of Engineering Thermodynamics. John Wiley &
Sons.
Sumeet Salunkhe: “Performance improvement of throttling calorimeter”, M.Tech Report, 2017