Investigation of the thermal stratification during the subcooled cryogenic propellant charging

• Cryogenic subcooled liquid oxygen charging methods were investigated. • Thermal stratification observed during the bottom charge of subcooled liquid oxygen. • Three different experimental results are validated according to Ri number. • The thermal stratification strengthens in lower gravity condition than the earth. This study explores thermal stratification phenomena in tanks under various conditions, focusing specifically on the influence of the Richardson number, inlet geometry, and gravitational variations. Initial experiments were conducted using liquid oxygen in small scale, followed by scaled-up experiments involving water and subcooled liquid oxygen, with comparisons made to previous research, including the X-33 tank tests. Experimental results revealed a significant correlation between the Richardson number and the degree of thermal stratification. Higher Richardson numbers resulted in clearer thermal boundaries and required more computational nodes for accurate numerical simulations. Specifically, Richardson numbers near 10 required about 1000 nodes, while lower numbers around 1 and below 0.001 required 200 and 20 nodes, respectively. Simulation results closely matched experimental data, validating the numerical approach and emphasizing the impact of inlet and outlet geometries. The X-33 experiment particularly illustrated a pronounced thermal stratification boundary, highlighting geometry’s critical role. Hypothetical analyses under Martian and lunar gravity conditions showed that lower gravitational environments increase the stratification length, requiring additional volumes of subcooled liquid to achieve uniform tank cooling. Mars conditions would see thermal stratification lengths increase by 5% over Earth conditions, whereas lunar conditions would increase stratification length by approximately 25% over total tank height. The findings from this study provide valuable guidelines for the design and operation of liquid storage tanks and propulsion systems across various gravitational settings, and establish a foundation for optimizing future computational simulation efforts based on the Richardson number.