Heat Transfer Behaviors on Combinational Insulation of Spray-On Foam and Variable Density Multilayer for Cryogenic Propellant Tanks

Abstract

Efficient and reliable thermal insulation for cryogenic propellant storage in orbit is an essential ingredient for long-duration missions in future space exploration. A new combinational thermal insulation composed of spray-on foam insulation (SOFI) and variable density multilayer insulation (VD-MLI), is suitable for cryogenic propellant storage due to its excellent heat insulation and light quality. Based on the heat transfer calculation model of SOFI/VD-MLI for ground and space stages, the variations of total heat flux through the combinational insulation with the thickness of SOFI and VD-MLI, the warm boundary temperature, and storage medium were analyzed. Comparison between numerical results and experimental results from the literature shows that the model is feasible to be applied in engineering. In the ground stage, the heat flux through the SOFI/VD-MLI decreases by approximately 92.7% with a SOFI thickness of 10 mm than 150 mm in the condition of constant VD-MLI thickness, and declines by 8.4% with the VD-MLI thickness of 10 mm than 150 mm in the condition of constant SOFI thickness. In the space stage, however, the descent degree of the heat flux is approximately 13% and 90%, respectively, in the corresponding aforementioned conditions. Because the warm boundary temperature is constant, the total heat flux through the combinational insulation will be less sensitive to the storage medium. Furthermore, variations in VD-MLI thermal resistance and heat fluxes by solid heat conduction and heat radiation with layer position presented a jumping change at the interface of different layer density regions. The results show that there is an optimal combination thickness for SOFI and VD-MLI on the ground and in space.