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Boiling Heat Transfer in ITER First Wall Hypervapotrons

Dennis Youchison, Mike Ulrickson and Jim BullockSandia National Laboratories

Albuquerque, NM

August 6, 2010

FNST/MASCO/PFC Meeting

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

under contract DE-AC04-94AL85000.

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Outline

• 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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• 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 .

Background

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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 criticalheat flux• Use Eulerian multiphase model in FLUENT & Star-CCM+• RPI model (Bergles&Rohsenow)• Features heat and mass transfer between liquidand 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/st=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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CCM+ boiling models were benchmarkedagainst US and Russian test data for rectangularchannels and hypervapotrons to within 10oC.

capability to predict CHF from CFD

Star-CCM+ Results

Surface temperature distribution, t=6.3 s

Case analyzed is a hot “stripe” on a section of the ITER first wall.

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With no boiling, heat transfer is highest under the fins

With boiling, the vapor fraction in grooves is 4%-6% on average

t=6.3 s

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. Iso-surface of 2% vapor volume fraction

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Star-CCM+ gives same h as Fluentfor 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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Te

mp

era

ture

(C

)

Thermocouple response 3.5 MW/m2 through 6 s

Russian data

Thermocouple response 4.0 MW/m2 through 6 s

Te

mp

era

ture

(C

)

ICHFTrip @ 400 C

Not ss yet!

Rectangular channelresults

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Russian HV CHF Mock-up

flow

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Total of 490k poly cells in mesh

Heated area is 100 mm x 48 mm

3 prism layers

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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

Russian data

4 s for TCs to ss

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Outlet temperature close to steady state.

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a) sub-cooledb) nucleate to transition boilingc) film boilingd) sub-cooled

All flow regimes can exist simultaneously.

4.0 MW/m2

115 oC, 2 MPa water1.0 m/s

T:

h:

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CHF Testing Testing of the HV mock-up

Water 2 m/sPabs 10 MW/m2

tpuls 300s

T/C (1.5 mm from CuCrZr surface)

Second pulse at 10 MW/m2)ICHF !