Theory and Technique for Reducing the Effect of Cracks in Multilayer Insulation from Room Temperature to 77 K

Abstract

Cracks or gaps in multilayer insulation blankets can significantly increase the heat load to a cryogenic system. Our experiments gave the mean equivalent thermal conductivity of a narrow crack to be 3 to 5 W/m-K between room temperature and 77 K. The heat flux through a crack was found to be ~150 W/m2. The dependence of the heat load on crack width, geometry, properties of the cold surface under the crack, the depth of the crack, and overall vacuum pressure were systematically studied. Aluminized Mylar patches covering the cracks were found to be very effective in reducing the heat load. Using the optimum number and distribution of patches determined in our experiments, it is possible to eliminate the effect of cracks on the overall heat load. In order to understand the mechanism of heat transfer through cracks, the temperature distributions in the multilayer insulation adjacent to cracks were measured. A theoretical model has been developed to explain this “black crack” phenomena and provide more quantitative heat leak estimates.KeywordsHeat FluxHeat LoadCrack WidthHeat Transfer MechanismCold SurfaceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.