Parameter Analysis and Performance Optimization of Thermodynamic Vent System in Cryogenic Tanks under Microgravity

To address the pressure control challenges in space cryogenic propellant tanks and achieve long-term on-orbit operation of cryogenic propellants under microgravity conditions, this study developed a self-pressurization model and a thermodynamic vent system （TVS） model for liquid hydrogen. The self-pressurization process in the liquid hydrogen tank under the influence of external heat leakage was studied. The formation mechanism of the thermal stratification phenomenon was revealed. By integrating orthogonal experimental design and FLUENT simulations, a total of 16 operating conditions with distinct parameter combinations were configured when TVS started to work. The effects of circulation pump flow rate, exhaust venting rate, nozzle size, and throttle valve backpressure on the pressure reduction process were analyzed. The influence weight of each parameter was quantified. With the goal of minimizing exhaust mass, a parameter optimization design was conducted. The results indicate that increasing the circulation pump flow rate can shorten the pressure reduction time. Under identical circulation pump flow rate conditions, a higher exhaust venting rate leads to lower inlet temperature of the main fluid stream and more rapid depressurization process. For the same exhaust venting rate, smaller nozzle sizes result in greater inlet velocity and shorter pressure reduction time. In terms of exhaust mass, the parameter significance ranking is: exhaust venting rate > circulation pump flow rate > nozzle size > throttle valve backpressure. The optimal values of each parameter were determined through analysis of the mean main effect plots. The optimal operating parameters were as follows: circulation pump flow rate of 0.04 kg·s⁻¹, throttle valve backpressure of 10 kPa, venting rate of 1%, and nozzle diameter of 0.005 m. This study provides a theoretical foundation for the design and control of TVS systems in cryogenic propellant tanks, with potential follow-up work including experimental validation and exploration of applicability under dynamic operating conditions.