Theoretical And Experimental Study On Variable Density Multi-Layer Insulation In Vaccum

With the development of deep space exploration, Technology oflong-term cryogenic propellants storage for space exploration has becomean effective method to solve the large-load and long-distance problem offuture resources development on the moon and explorations of outer spacesuch as Mars. In order to realize this technology, design of efficient, lightand safe cryogenic isolation is necessary. Under this situation, multilayerinsulation became more and more important in cryogenic storage. Whiletraditional vacuum multilayer insulation uses a unified layer density alongthe thichness, which rarely takes into account the fact that some parameterschange along the thichness. So it cannot gain the best thermal insulationperformance of the MLI material. Thus Variable Density MultilayerInsulation(VD-MLI) was put out.Variable Density Multilayer Insulation is a new type of MultilayerInsulation It changes the layer density along thichness to improve thethermal insulation performance.The thermal insulation performance of VD-MLI is studied. At first, theapplication background and impact factors of multilayer insulation issummarized. Then the concept of variable density multilayer insulation isintroduced. Furthermore, our own view of variable density distribution isproposed. In this article, we think the performance optimization forvariable density multilayer insulation requires two comprehensive consider,including the law within the multilayer insulation and spacer materialcharacteristics. Then the layer by layer model is used for further theoreticalstudies. Through this analytical model, the optimized layer densitydistribution is calculated and summarized, meanwhile the insulation performance improvement brought by variable density distribution isstudied. According to these analyzes，we learnt that to improve the thermalinsulation performance, the layer density near the cold boundary should berelatively small. And the thermal insulation performance is optimizedwhen the layer density near the cold boundary is about1/2of the averagelayer density. To verify the theoretical predictions by the modifiedlayer-by-layer model, an experimental apparatus for insulationperformance test is designed and fabricated. Afterward experiments onVD-MLI is carried out. According to the experimental data, the bestthermal insulation performance is reached when the layer density near thecold boundary is about1/2of the average layer density. This well fit thetheoretical predictions which means the layer by layer mode is a suitabletheoretical model for VD-MLI. At last, the heat flux change trend of eachdensity distribution versus warm boundary temperature is discussed.