Study on Performance Improvement of Composite Thermal Insulation Structure Combining Vapor Cooled Shield by Integrating Para-ortho Hydrogen Conversion

To explore the effect of integrating different types of para-ortho hydrogen conversion with the Variable Density Multilayer Insulation （VDMLI） structure combining one Vapor Cooled Shield （VCS） on thermal insulation performance improvement of liquid hydrogen storage tanks, a steady-state heat transfer model for the composite insulation structure with the continuous and adiabatic para-ortho hydrogen conversion was established. The influence of the VCS position and the para-ortho hydrogen converter position on the insulation performance of the composite insulation structure was analyzed. The results show that the performance of the insulation structure with the continuous conversion is better than that with the adiabatic conversion. The minimum heat leakage of the structure with the continuous conversion is 0.1175 W·m⁻², 13.48% less than that without para-ortho hydrogen conversion. If the adiabatic conversion is used, the minimum heat leakage can reach 0.1210 W·m⁻² with a reduction of 10.30% compared with that without para-ortho hydrogen conversion, when the ratio of the distance between the converter and the VCS tube inlet to the total length of the VCS tube is 30% to 77.5%. When the converter is installed near the middle of the tube, the initial temperature of the adiabatic conversion and the heat absorption during the conversion can be increased, which is beneficial to offset the external heat flux and improve the thermal insulation performance. This study provides quantitative theoretical basis and technical guidance for the design of the composite insulation structure in liquid hydrogen temperature range.