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

Abstract

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