The development of a novel apparatus to measure the emissivity of high-roughness materials at 82 K

Abstract

The emissivity of a material changes with temperature. The knowledge of emissivity plays an important role in the estimation of radiation heat load in cryogenic systems. As the emissivity values of different materials at cryogenic temperatures are scarcely available in the literature, room-temperature emissivity values have been extensively used to estimate the radiation heat load in cryogenic systems. This may lead to a significant deviation between the predicted and actual radiation properties at cryogenic temperatures. Therefore, in the present work, an apparatus is developed based on a calorimetric technique for measuring the emissivity of an opaque material around 82 K. The novelties of the apparatus are its compact size, ease of sample handling, shorter time required to reach thermal equilibrium and, most importantly, capacity to measure the emissivity of a sample of high roughness. To understand the effectiveness of low and high emissivity-coated heat radiators for the system, a theoretical and an experimental approach has been followed. It is found that the high-emissivity heat radiator leads to a significant reduction in the time required to reach thermal equilibrium compared to a low-emissivity heat radiator. To verify and validate this setup, the emissivities of Aeroglaze Z306 (high emissivity) and Cu (low emissivity) are measured and compared with the values reported in the literature. Finally, this work has been extended to measure emissivity at cryogenic temperature for the first time for PU1, SG121FD and indigenously developed novel materials, such as black paints, adhesive and activated charcoals of different granule sizes.