1. DL Youchison 5931/31.02 1 Boiling Heat Transfer in ITER First Wall Hypervapotrons Dennis Youchison, Mike Ulrickson and Jim Bullock Sandia 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.

2. DL Youchison 5931/31.02 2 Outline What are hypervapotrons? Why hypervapotrons? Geometry optimization Boiling heat transfer in hypervapotrons –Why CFD? Benchmarking with HHF test data CHF prediction

3. DL Youchison 5931/31.02 3 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

4. DL Youchison 5931/31.02 4 ITER First Wall 04

5. DL Youchison 5931/31.02 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

6. DL Youchison 5931/31.02 6 What are hypervapotrons? Hypervapotron FW “finger”

7. DL Youchison 5931/31.02 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

8. DL Youchison 5931/31.02 8 Velocity distributions 5 MW/m 2 400 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.

9. DL Youchison 5931/31.02 9 Star-CCM+ 560 k polyhedra mesh Switches from Eulerian multi-phase mixture to VOF for film boiling.

10. DL Youchison 5931/31.02 10 CCM+ boiling models were benchmarked against US and Russian test data for rectangular channels and hypervapotrons to within 10 o C. 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.

11. DL Youchison 5931/31.02 11 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

12. DL Youchison 5931/31.02 12 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/m 2 K.

13. DL Youchison 5931/31.02 13 Systematic parameter study performed on rectangular channels – then applied to hypervapotrons.

14. DL Youchison 5931/31.02 14 Temperature (C) Thermocouple response 3.5 MW/m 2 through 6 s Russian data Thermocouple response 4.0 MW/m 2 through 6 s Temperature (C) ICHF Trip @ 400 C Not ss yet! Rectangular channel results

15. 15 Russian HV CHF Mock-up flow

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

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

18. 18 CCM+ solid/fluid interface temperatures for 6.0 MW/m 2 @6s

19. 19 Vapor fraction – 6.0 MW/m 2 @6s

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

21. 21 Outlet temperature close to steady state.

22. DL Youchison 5931/31.02 22 a)sub-cooled b)nucleate to transition boiling c)film boiling d)sub-cooled All flow regimes can exist simultaneously. 4.0 MW/m 2 115 o C, 2 MPa water 1.0 m/s T: h:

23. DL Youchison 5931/31.02 23 CHF Testing Testing of the HV mock-up Water 2 m/s P abs 10 MW/m 2 t puls 300s T/C (1.5 mm from CuCrZr surface) Second pulse at 10 MW/m 2 ) ICHF !