Optimizing variable-density configurations: A multi-objective study on multilayer insulation performance

The number of density regions and the ratio of radiation shields within each density region for variable-density multilayer insulation (VDMLI) is the key to high vacuum insulation technology. To further improve the thermal performance of multilayer insulation (MLI) structure applied to cryogenic vessel, the NSGA-II-LINMAP method is employed in the optimization of VDMLI. The heat flux and the insulation thickness are defined as optimization objectives, and the optimal variable-density configurations under different working conditions are calculated. Additionally, the influences of different operating conditions on the heat flux as well as on the optimal variable-density configuration are analyzed. The results show that the heat flux decreases with an increase in the number of radiation shields, a decrease in the hot boundary temperature, an increase in the cold boundary temperature, and a higher vacuum level. When the number of radiation shields is fewer than or equal to 50 layers, the MLI structure consists of medium-density region and high-density region, with the medium-density region accounting for 20% of the total radiation shields. When the number of radiation shields is more than 50 layers, the VDMLI transitions to a configuration of low-density region and high-density region, where the low-density radiation shields comprise 10% of the total radiation shields. Furthermore, for identical radiation shields, the heat flux for VDMLI is 12.51% ∼ 16.10% lower than UDMLI; whereas for the same thickness, it reduces heat flux by 5.70% ∼ 9.00%; for the same thermal insulation performance, the thickness of VDMLI is 5.37% ∼ 8.47% thinner than the UDMLI.