The Heat Transfer Study Of Cryogenic Vapor Cooled Shield Compounded Insulation

The thermal protection technology has a great influence on the heat leakage of the tank,especially in the aerospace, the using of efficient thermal protection technology will significantly reduce the heat leakage of the tank and the evaporation loss of cryogenic propellant, and the zero boil-off storage of cryogenic propellants will be realized. The compounded insulation, which consists of vapor cooled shield insulation, Spray-on Foam Insulation, and Variable- Density Multilayer insulation is a new and efficient thermal insulation technology of cryogenic storage tank, and has the advantages of excellent heat insulation and light weight. It can further satisfy the demand of the heat leakage of cryogenic storage tank in the ground, launching and on-orbit stages of aircraft, and also is the more desirable form of thermal protection.The vapor cooled shield compounded insulation of cryogenic storage tank was taken as the research object. For the vapor cooled shield compounded insulation, the heat transfer mechanism was analyzed, the heat transfer model was established and calculated, and the numerical simulation of temperature fields was studied. The main research works and conclusions are as follows:(1)The heat transfer mechanisms of the vapor cooled shield compounded insulation in the ground and space stages. The ground stage being the atmospheric environment, the gas conduction between adjacent reflectors of VD-MLI do exist, SOFI plays a main role to thermal insulation. In the space stage, the gas conduction between adjacent reflectors of VD-MLI can be ignored due to high vacuum. The insulation performance of VD-MLI is better than that of SOFI, and VD-MLI plays a main role. On this foundation, the heat transfer models in the ground and space stages were established respectively.(2)The vapor cooled shield compounded insulation in the ground and space stages were calculated by MATLAB. The result showed that during the ground stage when the vapor cooled shield is placed in the position between SOFI and VD-MLI, the heat insulation effect of the vapor cooled shield compounded insulation is the best, and during the space stage, the tank heat-leak will increase as the shield lies in the outside or inside of VD-MLI, it will get the optimal heat insulation effect for the vapor cooled shield to be placed near the middle position of VD-MLI. Taking into account that the spacecraft is in orbit most of the time, the final optimal heat insulation effect for the vapor cooled shield should be placed near the middle position of VD-MLI.(3)To ensure heat transfer sufficiently between cryogenic gas and inner wall of coil,among all the lengths of coil calculated in ground stage and space stage, the optimum length should be the greatest. The coil thickness is 1mm,the coil external diameter is 7 mm, the optimal coil lengths of cryogenic storage tanks with liquid nitrogen, liquid oxygen and liquidmethane are 8.18 m, 8.88 m, 11.61 m, the number of turns are 2,2,3 respectively.