Multi-parameter optimization of multiple vapor-cooled shields integrated with para-to-ortho catalytic conversion based on self-pressurization model of liquid hydrogen tank and MOGA

The temperature difference between the inside and the outside of liquid hydrogen storage tank is very large, so VMLI (vacuum multi-layer insulation) coupled with VCS (vapor cooled-shield) is generally introduced to shield external heat leakage. Further, VCS is filled with catalyst for hydrogen para-to-ortho catalytic conversion (POC), which can release cold energy to shield the external heat leakage. Based on the self-pressurization model of tank constructed in the research, it is found that the mass flowrate in VCS ṁ_vcs, the opening moment of VCS t_open, the duration time of VCS t_d, and VCS DP(dimensionless position) have obvious effect on the total mass of gas hydrogen consumed by VCS and the dormancy of tank, which are respectively described by two dimensionless factors λ_c and λ_d. It is hoped that the tank dormancy can be extended with as little hydrogen consumed by VCS as possible, by choosing appropriate (ṁ_vcs,t_open,t_d,VCS DP). Especially for TVCS, six parameters need to be determined, including (ṁ_vcs,t_open,t_d) and DP of the three VCSs. Therefore MOGA (Multi-objective genetic algorithm) is innovatively introduced to help search for the optimized (ṁ_vcs,t_open,t_d,VCS DP) in high-dimensional input parameter space, which can make λ_c and λ_d Pareto-optimal, and the corresponding (λ_c, λ_d) form the Pareto front. The Pareto front can be fitted as a straight line through the origin. The slope parameter of the line determines the theoretical limit of λ_d when λ_c is fixed. It means that, when the total mass of gas hydrogen consumed by VCS is fixed, the dormancy has a theoretical limit. When the TVCS-POC (triple vapor-cooled shield integrated with hydrogen para-to-ortho catalytic conversion) is adopted, (λ_c, λ_d) calculated according to the optimized (ṁ_vcs,t_open,t_d,VCS DP)(the three optimized points in high-dimensional input parameter space) are compared with that calculated according to the initial (ṁ_vcs,t_open,t_d,VCS DP). It is found that λ_c corresponding to the optimized points 1,2 and 3 decrease by 5.57%, 18.60% and 31.57% respectively, while λ_d increase by 64.57%, 42.60% and 20.25% respectively. It reveals that, after adjusting (ṁ_vcs,t_open,t_d,VCS DP), the total mass of gas hydrogen consumed by VCS is reduced while the dormancy is extended.