Computer analysis of transient heat transfer from coated surfaces

Abstract

The transient thermal response of internally heated, coated surfaces in contact with liquid helium was investigated with a previously developed computer model. The coatings were found to affect the time required to initiate film boiling or to quench a superconductor in the substrate. The energy which can be absorbed without an unacceptably large temperature rise depends most strongly upon the coating thermal property group (kpC p )½and on the peak nucleate boiling heat flux. Dielectric materials for electrical insulation usually have low thermal property group values, but a new class of ceramic materials shows great promise for application with superconducting devices aselectrical insulations with good thermal properties. Coating materials with thermal property group values greater than that of OFHC copper at liquid helium temperatures provide the same thermal stability as a bare copper surface exposed to the helium bath. Possible applications of the new materials to potted windings are also discussed.