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An inexpensive calorimeter for comparing and evaluating the performance of evacuated multilayer insulation materials between ambient and cryogenic temperatures for varying thicknesses is described and discussed. Simply stated, the calorimeter comprises an easily dismantleable dewar which provides for convenient replacement of insulation and thus incorporates in the measured k-value the influence of overlapping of joints which commonly exists in practical applications. The heat-transfer rate is measured by boiloff of cryogenic fluid. Utilizing a completely wrapped dewar eliminates or minimizes the edge effects which are a major factor in the testing of anisotropic multilayer insulation. Estimated errors and design considerations which reduce the errors to a minimum are discussed. The chief advantages of this type of calorimeter are its low cost, simple operation, and the fact that it most nearly duplicates, in many cases, the expected use conditions of the insulation. Principal limitations are the difficulty of measuring the thermal conductivity at variable temperatures on the warm side and the impossibility of measuring thermal conductivity of insulation as a function of compressive load. Selected results for some of the more common multilayer insulations with temperature interval from ambient to LN2 and LH2 for various thicknesses of insulation and layer densities are presented.
thermal insulation, lamina, calorimeter, cryogenics, thermal conductivity, anisotropy, low temperature, heat transfer
De Haan, J. R.
Research specialist, Cryogenic Engineering Co., Denver, Colo.