The thermal conductivity of cryogenic insulation materials and its temperature dependence

For the presentation of the thermal conductivity of cryogenic insulation materials and their integral mean values an empirical function is suggested, with which experimentally found values can be extrapolated to other temperature levels. The selection of materials includes granulated and fibrous insulations under atmospheric pressure as well as under vacuum and a multilayer insulation for most high performances. It is shown theoretically, how the constants in the empirical function can be determined. Their calculation is demonstrated practically by using real measurements. For a multilayer insulation a theory is developed, with which a measured value can be extrapolated to other temperatures, gas pressures and numbers of layers. Its application to a real insulation system is demonstrated too. The results are listed in a tabular summary. (C) 2006 Elsevier Ltd. All rights reserved.