Effective thermal conductance from a thin film into liquid helium

The steady-state thermal dissipation from heat-generating thin-film strips, immersed in liquid helium, has been examined by measuring the thermal hysteresis of the magnetically induced resistive transition of superconducting thin films of tin, deposited onto glass and aluminum substrates. The dissipated heat was found to depend linearly on the temperature difference between the film strip and the helium bath. It was thus possible to characterize the heat transfer by an effective coefficient of heat transfer that was approximately ten times as great for films on aluminum substrates as for films on glass substrates. For a 0.12-×2.3- mm2 film strip, its value was approximately 8×10-3 W/°K for the aluminum substrate, approximately 9×10-4 W/°K for the glass substrate. The coefficient was also dependent on the nature of other thin films deposited beneath or above the film strip. Analysis of the data indicated that the thermal conductance between the film strip and the helium bath was about 0.1 W/cm 2°K, and the thermal conductance between the film strip and the aluminum about 1.7 W/cm2°K. © 1964 The American Institute of Physics.