Insulation Performance of Vacuum-MLI Cavity Under Varying Residual Gas Pressure: Analytical Study and Application to Liquid Hydrogen System

In this study, the influence of residual gas pressure within a vacuum insulation cavity on the insulation performance of a multi-layer insulation (MLI) system was investigated through thermal analysis. Based on an electrical analogy, a thermal resistance network was constructed, considering heat transfer through the insulation system by gas conduction, solid conduction, and surface radiation. Lees’ four-moment model was employed to calculate the gas conduction across a wide range of vacuum conditions, including medium-to-low vacuum situations. The analysis shows that total heat flux and effective thermal conductivity exhibited non-linear increases as the pressure approached atmospheric level. This trend was successfully validated by comparisons with experimental data from the literature, thereby confirming the rationality of the proposed analytical model. Furthermore, the contributions of individual heat-transfer modes to the total heat flux within the insulation system were scrutinized, thereby revealing their redistribution patterns. Under high-vacuum conditions, solid conduction and radiation were the primary modes of heat transfer. However, with increasing pressure, the proportion of gas conduction rose markedly, becoming the primary heat-transfer mode under medium-vacuum and low-vacuum conditions. Finally, a validated analytical technique was utilized to predict heat-transfer characteristics under cryogenic boundary conditions associated with liquid hydrogen storage.