page 1 of 8 Concept development of pin-fin cooled divertors M. S. Tillack ARIES Project Meeting July 2010

page 2 of 8 Background Recent component design and analysis at UCSD has emphasized jet-cooled concepts Thermal-hydraulic studies at Georgia Tech have considered pin-fin cooling to improve thermal performance Goal:  Develop a work plan that integrates these activities and evolves reference concepts In this talk:  Fabrication and materials issues  Analysis approach  Discussion

page 3 of 8 Fabrication of pins is an additional burden for these concepts Electric Discharge Machining  Doesn’t scale well to reactors – too slow Slitting saw (hexagonal array)  Not sure it will work with W, high tool wear likely Hole drilling and brazing of pins  Too many brazes, high a probability of failure Laser machining  Ultrashort lasers provide no heat-affected zone Electrochemical machining  The inverse of electroplating

page 4 of 8 Fundamentals of Electrochemical machining

page 5 of 8 Electrochemical machining looks promising Commonly used in mass production Used for working extremely hard materials or materials that are difficult to machine using conventional methods Can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals such as titanium, hastelloy, kovar, inconel and carbide ~mm/minute speeds No tool wear Extensive literature on the subject, e.g. Adopted by EU for their divertor

page 6 of 8 Pins can be added to either plate or finger concepts Per Malang, pin fins on plates are not advantageous, because the plate concept can reach only 10 MW/m 2 and jets work fine up to that point. According to GT experiments, there appears to be modest benefit in using pin fins in the finger concept. Reverse flow is better than forward flow.

page 7 of 8 Thermomechanical analysis approach  Separate thermal hydraulics (GT) and thermomechanics (UCSD)  Pins themselves should not see high stress levels  No differential thermal expansion  Small temperature gradients  Relatively unconstrained  We could verify this with simple analysis  Can be treated as a heat transfer enhancement on existing models of plate and finger concepts  In any case, we would need to start over due to ANSYS compatibility issues from v.11 to v.12

page 8 of 8 Discussion and conclusions 1.Pins provide additional challenge of fabrication, and possibly reliability concerns. 2.Not clear pins offer an advantage. Finger design Thermal hydraulics studies suggest finger design sees only modest benefit from the use of pin fins. Further optimization may improve this. Plate design We can easily analyze the plate concept, although a new model (using ANSYS v.12) needs to be built  Using T w (or h and T b ) from GT, or using scaled values 3.Should we proceed with analysis?