Optimization of Radiation Shields Parameters in Multi-Layer Thermal Insulations

Multi-layer thermal insulations are fabricated by locating consequtive porous insulation and radition shields, which could be used at high temperature and cryogenic applications. In this type of insulations, different heat transfer methods such as conduction, convection and radiation would be occurred, although by using high density insulation (more than 20 kg/m^3 ), convection could be neglected. In this paper, radiation shiels parameters such as thickness, emissivity, distance and number of screens are studied and optimized. For investigating the effect of these parameters on effective thermal conductivity of multi-layer thermal insulation, a mathematical code has been improved in EES software. Then, the obtained results have been validated by another study. Moreover, Powell method has been applied in order to optimize the parameters. The results show that the amount of shield emssivity and shields arrangement have the most impact on the effective thermal conductivity of multi-layer thermal insulations. Also, the optimized distances between radiation shields indicate that this distance increased in the direction of heat transfer.