Experimental Investigation of Thermal Properties of Materials Used to Develop Cryopump

A cryopump works on the principle of cooling down a metal surface or a surface coated with a porous material, namely, cryopanels, to cryogenic temperature. The gases stick to cryopanels thus lowering pressure and thereby creating a vacuum in an enclosed space. Materials used in the development of cryopumps include metals like copper and steel as structural materials, composite material like G10 for supports, thermal insulation, adhesive to fix sorbent to the metal surface, Vespel as an insulator, and various kinds of coatings on metal surfaces. Thermal properties govern heat load management and thereby the temperature of the cryopanels and hence pumping phenomena. This paper focuses on the experimental investigation of properties like specific heat, thermal diffusivity, thermal conductivity of materials, and their variation with lowering of temperature to cryogenic levels. A study was carried out to quantify the thermal properties of adhesive to fix the sorbent, the metal sheet of the cryopanel coated with activated charcoal granules using the adhesive, materials like G10 and Vespel, and high-emissivity black coating. The thermal conductivity (studied up to −150°C) for different kinds of adhesives was found to be in the range of 0.48 to 0.9 W/m‧K; for Vespel SP21 and G10, it is 0.58 and 0.8 W/m‧K, respectively. The emissivity at room temperature of the sorbent-coated cryopanels was 0.94, and for the high-emissivity black coating, it was in the range of 0.93 to 0.94.