Study On Heat Transfer Characteristics Of Multilayer Insulation Structure Of Low Temperature Propellant Tank

Multi-layer insulation structure plays an important role in the insulation process of cryogenic propellant tank.In this paper,the thermal insulation performance of multi-layer insulation structure in vacuum and ground environment is analyzed.This paper first introduces the heat transfer theory of multi-layer adiabatic structure,introduces the radiation heat transfer of multi-layer adiabatic structure reflective screen,the solid heat conduction of spacers and the heat conduction of residual gas between layers.Based on these theories,the model is established under different conditions..Considering the radiation heat transfer of multi-layer reflecting screen and the solid heat conduction of spacer,a heat transfer model of multi-layer insulation structure in vacuum is established.Based on this model,the heat transfer effects of thermal boundary temperature and the number of reflecting screen layers on multi-layer insulation structure are studied.It is concluded that the heat flow of multi-layer insulation structure increases with the increase of thermal boundary temperature and the number of reflecting screen.The effect of layer density on heat transfer of multi-layer adiabatic structure is studied.It is found that there exists an optimal layer density when the thermal boundary temperature is low.Several different variable density multilayer insulation structures were analyzed.It was found that when the total thickness of the total layers was constant,the variable density multilayer insulation materials could achieve better insulation effect,and the performance was improved by4.8%.Considering the pressure changes at different locations of the multi-layer insulation structure,a new heat transfer model of the multi-layer insulation structure in the ground environment is established.The new heat transfer model is compared with the traditional multi-layer insulation structure analysis model.It is found that when the vacuum is small,the calculation gap between the two models is large and the heat flux calculated by the new model is high.The influence of heat flux density of multi-layer insulation structure on interlayer pressure and interlayer gas is analyzed by using the newly established model.It is concluded that heat flux density of multi-layer insulation structure decreases with the decrease of interlayer pressure,but after the pressure reaches 10^-3 pa,the change of heat flux density is very small,so the multi-layer insulation structure wants to achieve good results.It is necessary to keep the vacuum below 10^-3 pa for heat transfer performance.By analyzing the heat flux density of several kinds of residual gases between layers,it is found that the heat flux density of multilayer insulation material is the smallest when the residual gases between layers are N₂.