FNST/MASCO/PFC Meeting
Boiling Heat Transfer in ITER First Wall Hypervapotrons
Dennis Youchison, Mike Ulrickson and Jim Bullock
Sandia National Laboratories
Albuquerque, NM
August 6, 2010
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy’s National Nuclear Security Administration
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under contract DE-AC04-94AL85000.
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Outline
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What are hypervapotrons?
Why hypervapotrons?
Geometry optimization
Boiling heat transfer in hypervapotrons
– Why CFD?
• Benchmarking with HHF test data
• CHF prediction
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Background
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Star-CCM+ Version 5.04.006, User Guide,
CD-adapco, Inc., New York, NY USA
(2010).
S. Lo and A. Splawski, “Star-CD Boiling
Model Development”, CD-adapco, (2008).
D.L. Youchison, M.A. Ulrickson, J.H.
Bullock, “A Comparison of Two-Phase
Computational Fluid Dynamics Codes
Applied to the ITER First Wall
Hypervapotron,” IEEE Trans. On Plasma.
Science, 38 7, 1704-1708 (2010).
Upcoming paper in the 2010 TOFE .
ITER First Wall 04
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Why hypervapotrons?
Advantages:
•High CHF with relatively lower pressure drop
•Reduction in E&M loads due to thin copper faceplate
•Lower Cu/Be interface temperature (no ss liners)
•Less bowing of fingers due to thermal loads
Disadvantages:
•CuCrZr/SS316LN UHV joint exposed to water
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What are hypervapotrons?
Hypervapotron FW “finger”
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Two-phase CFD in water-cooled PFCs
Problem: conjugate heat transfer with boiling
• Focus on nucleate boiling regime below critical
heat flux
• Use Eulerian multiphase model in FLUENT & Star-CCM+
• RPI model (Bergles&Rohsenow)
• Features heat and mass transfer between liquid
and vapor, custom drag law, lift or buoyancy and influence of bubbles on
turbulence
• CCM+ transitions to a VOF model for the film when vapor fraction is high
enough – need to know when to initiate VOF
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Velocity distributions
5 MW/m2
400 g/s
t=2.05s
Drag on bubbles, lift or
buoyancy, changes in
viscosity and geometry,
all affect the velocity
distribution under the
heated zone.
2mm-deep teeth
and 3-mm spacing
optimized to
produce a simple
reverse eddy in
the groove.
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Star-CCM+ 560 k polyhedra mesh
Switches from Eulerian multi-phase mixture to VOF for film boiling.
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Star-CCM+ Results
Case analyzed is a hot
“stripe” on a section of
the ITER first wall.
CCM+ boiling models were benchmarked
against US and Russian test data for rectangular
channels and hypervapotrons to within 10oC.
Surface temperature distribution, t=6.3 s
capability to predict CHF from CFD
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Star-CCM+ Results
Case analyzed is a hot “stripe” on a
section of the ITER first wall.
The details of the heat transfer change
dramatically as boiling ensues.
With no boiling, heat transfer
is highest under the fins
Iso-surface of 2% vapor volume fraction
With boiling, the vapor fraction in
grooves is 4%-6% on average
t=6.3 s
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Star-CCM+ gives same h as Fluent
for nucleate boiling.
Heat transfer coefficients
increase in grooves where
boiling takes place ranging from
12,000 to 13,000 W/m2K.
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Systematic parameter study performed on rectangular
channels – then applied to hypervapotrons.
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Rectangular
channel
results
Temperature (C)
Thermocouple response 3.5 MW/m2 through 6 s
Russian data
Temperature (C)
Thermocouple response 4.0 MW/m2 through 6 s
ICHF
Trip @ 400 C
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Not ss yet!
Russian HV CHF Mock-up
flow
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Total of 490k poly cells in mesh
3 prism layers
Heated area is 100 mm x 48 mm
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Surface temperature – 6.0 MW/m2, 1 m/s 115 C inlet, 2 MPa
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CCM+ solid/fluid interface temperatures for 6.0 MW/m2 @6s
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Vapor fraction – 6.0 MW/m2 @6s
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Thermocouple response through 6 s
4 s for TCs to ss
Russian data
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Outlet temperature close to steady state.
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All flow regimes can exist simultaneously.
T:
h:
a)
b)
c)
d)
sub-cooled
nucleate to transition boiling
film boiling
sub-cooled
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4.0 MW/m2
115 oC, 2 MPa water
1.0 m/s
CHF Testing
Testing of the HV mock-up
T/C (1.5 mm from CuCrZr surface)
Second pulse at 10 MW/m2)
ICHF !
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Water 2 m/s
Pabs 10 MW/m2
tpuls 300s