Numerical Calculation And Experimental Study On Thermal Contact Conductunce In Mutli-Layer Insulation

The peak of R&D movement of multi-layer insulation (MLI), the so-called"super insulation", began in 1960s. However, due to the hardness of solving questions of interlayer solid heat conduction and residual gas conduction, the pace of research has been slowed.This thesis tries to solve the two questions mentioned above, so the breakthrough in theoretical research could facilitate the utilization of MLI in practical engineering. Firstly, an ideal heat transfer model is proposed,(namely,in this model,only radiation heat transfer occurs in ideal multilayer insulation which the reflector is installed without spacerand contact)by using this model,the smallest limit of real multilayer insulation can be numerically calculated through Newton interative method,so the better comparison of insulating efficiency among different real multilayer insulation becomes feasible; Secondly a layer-by-layer heat transfer model based on separation of three ways of heat transfer inside layers (that is, solid contact conduction, residual gas conduction and radiation) is built. Through summing up all the unknown influences of diversified factors related with solid contact conduction to a coefficient of"f", which stands for the ratio between actual contact area and nominal contact area between two contacting solids, the model gets the calculated total heat flux and corresponding heat flux of solid thermal contact conductance, radiation and residual gas conduction, the results indicate that the errors are within 10%, which undoubtedly proves the validity of this model. At the same time, the calculated temperature distribution of shields is coincided with the experimental results.Next focus is experimental study of different multilayer insulation and effective thermal conductivity of fiber sheets .First by testing the practical multilayer insulation in a cryogenic tanker, which is the carilometer in my paper,some affecting factors on multilayer insulation are analysed, then by using the low-temperature and vacuum environment caused by multilayer insulation, the effective thermal conductivity of multiple fiber paper with 5 layers is tested.Through Newton interativemethod,an empirical formula is deduced to computer the thermal conductivity of fiber paper,The errors between experimental thermal conductivity and the calculated conductivity by empirical formula are below10%,so the formula of fiber conductivity can be applied to practical enginnering. Finally, based on the assumption that the thermal contact resistance is much larger than other thermal resistance caused by gas conduction and bulk solid conduction among the fiber sheets, the thermal contact resistance at the interface of two layers of fiber paper is calculated, the results are comparable with other experimental results in the literature.