Evaluation of Multilayer Insulation Performance Equations Available in the Literature

Abstract

MLI blankets are the thermal insulation materials used in cryogenics, spacecraft applications and many other sectors. In literature, there are several equations to predict the thermal performance of MLI blankets. In the content of the thesis, some of heat flux predicting equations in the literature were investigated. The accuracy and the validity of these equations were discussed by using existing in-house experimental results of 8 and 22 layer MLI blankets. In order to utilize these equations, the specifications and the parameters of MLI blankets required for these equations were defined. According to these parameters, iterative and direct numerical computing codes were generated using a commercial software to predict the heat flux results of 8 and 22 layer MLI blankets with respect to different cold boundary temperatures. Obtained heat flux results of these equations were compared with experimental steady state heat flux results to observe the accuracy of these equations. Based on the studies carried out for the thesis, it was concluded that the Layer by Layer MLI Calculation Using a Separated Mode and Doenecke equation is able to predict the heat flux through MLI blankets successfully at the cold boundary temperature of -127°C and -75°C for the MLI blankets with different number of layers. However, Modified Lockheed equation gives unsatisfactory predictions at the same cold boundary temperatures. Obtained heat flux results of these equations were also compared with each other. Based on observations, it was concluded that the Layer by Layer MLI Calculation Using a Separated Mode and Doenecke equation gives similar results for the same cold boundary temperatures.