Improved pool boiling heat transfer to helium from treated surfaces and its application to superconducting magnets

Abstract

Experiments reported here show that greatly increased heat transfer to a pool of boiling helium can be achieved by treating the surface being cooled. The essence of the treatment appears to lie in covering or partly covering the surface with a thin layer (~ 25 μm) of material of low thermal conductivity and low heat capacity (this feature is partly supported by theory): the superposition of rough particles (~ 100 μm) or porous material gives even greater improvement. The peak nucleate boiling heat flux is increased but the most marked effect is the increase in minimum film boiling heat flux by a factor of up to about 4 compared with a smooth copper surface. This phenomenon is useful in the construction of cryostatically stabilised magnets permitting the use of less copper stabilising material. An experiment is reported showing the increase in the recovery current in a typical conductor resulting from treating the surface.