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Boiling Heat Transfer in ITER First Wall Hypervapotrons

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.

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Boiling Heat Transfer in ITER First Wall Hypervapotrons

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  1. 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 under contract DE-AC04-94AL85000. 1

  2. Outline • What are hypervapotrons? • Why hypervapotrons? • Geometry optimization • Boiling heat transfer in hypervapotrons • Why CFD? • Benchmarking with HHF test data • CHF prediction 2

  3. Background • 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 . 3

  4. ITER First Wall 04 4

  5. 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 5

  6. What are hypervapotrons? Hypervapotron FW “finger” 6

  7. 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 7

  8. 5 MW/m2 400 g/s t=2.05s Velocity distributions 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. 8

  9. Star-CCM+ 560 k polyhedra mesh Switches from Eulerian multi-phase mixture to VOF for film boiling. 9

  10. Star-CCM+ Results CCM+ boiling models were benchmarked against US and Russian test data for rectangular channels and hypervapotrons to within 10oC. Case analyzed is a hot “stripe” on a section of the ITER first wall. Surface temperature distribution, t=6.3 s capability to predict CHF from CFD 10

  11. With no boiling, heat transfer is highest under the fins With boiling, the vapor fraction in grooves is 4%-6% on average 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 t=6.3 s 11

  12. 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. 12

  13. Systematic parameter study performed on rectangular channels – then applied to hypervapotrons. 13

  14. Thermocouple response 3.5 MW/m2 through 6 s Thermocouple response 4.0 MW/m2 through 6 s Russian data ICHF Trip @ 400 C Temperature (C) Not ss yet! Temperature (C) Rectangular channel results 14

  15. Russian HV CHF Mock-up flow 15

  16. Total of 490k poly cells in mesh 3 prism layers Heated area is 100 mm x 48 mm 16

  17. Surface temperature – 6.0 MW/m2, 1 m/s 115 C inlet, 2 MPa 17

  18. CCM+ solid/fluid interface temperatures for 6.0 MW/m2 @6s 18

  19. Vapor fraction – 6.0 MW/m2 @6s 19

  20. Thermocouple response through 6 s 4 s for TCs to ss Russian data 20

  21. Outlet temperature close to steady state. 21

  22. All flow regimes can exist simultaneously. T: h: • sub-cooled • nucleate to transition boiling • film boiling • sub-cooled 4.0 MW/m2 115 oC, 2 MPa water 1.0 m/s 22

  23. CHF Testing Testing of the HV mock-up T/C (1.5 mm from CuCrZr surface) Water 2 m/s Pabs 10 MW/m2 tpuls 300s Second pulse at 10 MW/m2) ICHF ! 23

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