Numerical investigation on helium pressurization behavior of cryogenic propellant in microgravity

Abstract

In deep space exploration, the pressurization of cryogenic propellant in microgravity is an essential technique of propellant transfer on orbit. In this study, a numerical model is newly developed based on an open source computational fluid dynamics (CFD) code OpenFOAM to address the helium pressurization of cryogenic fluids in microgravity. The model incorporates phase change model, species transfer model, and interface reconstruction to predict the interface, temperature and concentration distributions. In the microgravity pressurization, weak buoyancy-driven convection prevents the formation of temperature and species stratification in the ullage. The smaller vorticity during microgravity pressurization results in reduced wall heat flux compared to normal gravity. The contact line of the solid–liquid interface reaches a maximum height of 122.5 mm, which leads to evaporation dominating the microgravity pressurization process. Fluctuations of gradually increasing amplitude at the interface result in localized gas stagnation, which reduces heat flux at the interface. This reduction in heat transfer from the gas phase subsequently leads to an increase in the pressurization rate to peak value. As a result, the combined effects of interface evaporation and the reduced heat flux at both the interface and inner wall lead to a higher pressurization rate under microgravity conditions compared to normal gravity. Specifically, the average pressurization rate in microgravity is approximately two times greater than in normal gravity. The findings of this study are crucial for enhancing the understanding and optimization of microgravity pressurization processes, offering valuable insights for future cryogenic propellant transfer systems in space exploration.