A quasi-2D thermodynamic model for performance analysis and optimization of liquid hydrogen storage system with multilayer insulation and vapor-cooled shield

Abstract

Liquid hydrogen (LH2) holds great potential in both aerospace and civil markets due to its high energy density. However, on account of the low boiling point and latent heat of vaporization of LH2, the high performance insulation storage system is the key to its efficient storage. One of the most efficient insulation methods for a LH2 storage system is considered to be Variable Density Multilayer Insulation (VDMLI) coupled with Vapor-Cooled Shield (VCS). This study establishes a quasi-two-dimensional (quasi-2D) thermodynamic model of liquid hydrogen storage system with VDMLI and VCS. The quasi-2D model incorporates the temperature gradient of VCS and its impact on VDMLI. The model can reveal the two-dimensional temperature and heat distribution in insulation systems, predict heat leakage and evaporation rate, and can be utilized for optimizing the design of the VCS structure. Using a NASA's tank as an example, the analysis conducted with the model indicates that the presence of VCS reduces the average temperature gradient of the inner VDMLI. The upper half of the tank exhibits a significantly smaller temperature gradient compared to the lower half, resulting in lower heat leakage. This effect becomes more pronounced as the VCS moves outward of the tank. Additionally, the VCS absorbs more heat in the inlet section than that in the outlet section, and this disparity becomes increasingly significant as the VCS moves outward of the tank. The model can also be employed to optimize the position of the VCS, resulting in a 69.73 % reduction in daily evaporation rate compared to NASA's original design. Lastly, a graphical method for the quick design of VCS structure is proposed which is based on calculated data for daily evaporation rate and apparent thermal conductivity. This method enables the retrieval of the corresponding apparent thermal conductivity based on the desired evaporation rate, facilitates the rapid determination of the range of VCS position, and allows for the quick prediction of the evaporation rate based on the VCS position. In conclusion, this research presents a new approach for the performance analysis and optimization design of liquid hydrogen storage system with VDMLI and VCS.