Conceptual Study on a Passive Thermodynamic Vent System for Long-Term Storage of Cryogenic Propellants in Space

In this study, the effects of the thermo-hydrodynamic characteristics of the two-phase flow discharged from the J-T device on the in-space storage duration of the cryogenic propellant is numerically investigated as a part of the conceptual design of a passive thermodynamic vent system (PTVS). For this purpose, a mathematical model is developed to predict the thermodynamic characteristics of a cryogenic propellant within a tank, as well as the heat transfer rate through a heat exchanger. Liquid oxygen (LOX) is selected as the cryogenic propellant. Using the developed model, the time-varying pressure, temperature, and mass of the propellant in the tank is investigated according to the exit vapor mass quality of the J-T device and the maximum allowable pressure of the tank, as input variables. The simulation results show that the cooling performance of the PTVS and the storage duration for the cryogenic propellant improve with higher exit vapor mass quality and lower maximum allowable pressure of the tank. For the range of input variables examined in this study, the longest storage duration is 150.4 days, showing an improvement of approximately 39.3% compared to the shortest duration of 107.9 days. The findings in this study provide a foundation for the comprehensive design of a heat exchanger and a J-T device that can maximize the long-term storage capability of a PTVS.