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A test apparatus was developed to measure the thermal conductivity of cryogenic insulations in a high-vacuum environment without the need of achieving thermal equilibrium throughout the specimen. In this device, the rate at which an insulated body (insulated with the material being evaluated) cools is used to determine the thermal diffusivity from which the thermal conductivity of the material can be calculated. The main advantages of such a calorimeter are: (1) the need for attaining steady state, which is extremely time consuming and difficult experimentally, is eliminated; and (2) thermal conductivities over a wide range of temperatures can be measured all in one experiment. Two versions of the apparatus, one for vacuum powder and the other for vacuum super insulations (alternate-layer types), have been built and are in use. They have been used to measure thermal conductivities ranging from 0.012 to 0.00012 Btu in./hr ft2 deg F, including materials with an anisotropic thermal-conductivity ratio of 30,000 to 1. The theory of operation, description of the apparatus, instrumentation requirements, test procedure, and an example of data reduction to numerical values are presented. A comparison of data obtained using the nonsteady-state apparatus and calorimeters of conventional steady-state design is made.
thermal conductivity, heat transfer, thermal insulation, cryogenics, low temperature, vacuum
Gibbon, N. C.
Section engineer, Union Carbide Corp., Tonawanda, N. Y.
Matsch, L. C.
Assistant technical director, Union Carbide Corp., Tonawanda, N. Y.
Wang, D. I-J.
Manager, Union Carbide Corp., Tonawanda, N. Y.