Experimental Investigation of Radiative Transfer Between Metallic Surfaces at Cryogenic Temperatures

Experimental measurements of the radiative heat flux between two parallel copper disks in the liquid-helium temperature range are presented. The temperature levels investigated were primarily for the higher temperature disk (emitter) at 10.0 deg K and 15.1 deg K and the lower temperature disk (receiver) at approximately 4.5 deg K. For the 15.1 deg K emitter temperature, the spacing was varied from 0.201 cm to 0.001 cm. For the 10 deg K emitter case, the spacing was varied from 0.044 cm to 0.005 cm. Experimental data at small spacings show a definite spacing dependence of radiative transfer which agree qualitatively with the predicted result. Based on the measurements at large spacings, an estimate of the total hemispherical emissivity for the copper surfaces in the liquid-helium temperature range indicates a value of 0.015, which is approximately one order of magnitude higher than predicted. The possible causes for the discrepancies are discussed.