Experimental study on composite insulation system of spray on foam insulation and variable density multilayer insulation

The composite insulation system of spray on foam insulation (SOFI) and multilayer insulation (MLI)/variable density multilayer insulation (VDMLI) is regarded as the most promising insulation system for cryogenic propellant in space application. In this paper, the composite insulation system composed of SOFI and MLI/VDMLI is studied in theoretical analysis and experimental testing. A test bed has been built to test the insulation performance of the insulation system. Heat leakage and temperature distribution of the insulation system were measured and analyzed. Theoretical calculation was carried out by “Layer by layer method” and “Lockheed method”. Composite insulation system was tested with simulated fluid of liquid nitrogen in high vacuum condition and atmospheric pressure condition, respectively. The test results show that the thermal resistance of SOFI accounts for only 0.12% of the total thermal resistance in high vacuum condition experiment, while 45.37% in atmospheric pressure condition experiment. With 50 layers of reflector, the measured heat leakage of VDMLI is lower than that of MLI by 13.57%, and heat flux decreases by 17.49%. By comparing the experimental results and the calculated value, it can be found that Lockheed method and Layer by layer method are suitable for calculating heat flux through MLI, but need to be improved in solving the temperature distribution.