Influence of condensed water on heat radiation absorptivity at cryogenic temperatures

Influence of water deposit on heat radiation absorptivity of a metallic surface was measured in a device designed for investigation of thermal radiative properties of materials at cryogenic temperatures. In this device heat transfer between planparallel surfaces of radiator and absorber is measured. An aluminium sample of 40 mm in diameter was used as absorber. A radiator consisting of an organic composite on a copper disk was used in two experiment stages. At temperature of 298 K, water outgassed from the organic layer formed the deposit on the absorber. Then the heat emitted from the radiator at temperatures from 45 K up to 250 K was used for the absorptivity measurement. Substantial influence of deposit of 85 mg/m2 on the sample absorptivity was found.