Thermodynamic behaviors of pressure-driven cryogenic non-vented filling under various gravity and thermal conditions

The non-vented filling (NVF) of cryogenic propellants is a key technology for in-space refueling. Existing numerical models commonly assume a constant inlet flow rate. In contrast, this study employs a transient computational fluid dynamics model featuring an instantaneous pressure-driven inlet boundary condition. This model is validated against ground-based liquid nitrogen NVF experiments. Validation results confirm that this model accurately reproduces the experimental wall temperature profiles and specifically achieves higher accuracy in predicting tank pressure than the conventional constant-flow assumption. Subsequently, the validated model is applied to conduct a systematic comparative analysis of the NVF process across varying gravity levels (normal, lunar gravity, and microgravity) and initial wall and inlet liquid temperatures. The results show that the gravity level governs the tank pressure and final filling level by modulating the competition between buoyancy and surface tension. Specifically, the normal and lunar gravity cases terminate prematurely due to the pressure limit. In contrast, the microgravity (30 μg₀) case achieves the target filling level at a lower final pressure, as the specific flow conditions promote interfacial condensation. Furthermore, under microgravity, a higher initial wall temperature promotes early evaporation and extends the filling duration, and a lower inlet temperature effectively moderates the overall tank pressurization by curtailing flash and providing greater subcooling. This work establishes a validated numerical framework, systematically quantifies the effects of key operational parameters, and provides critical insights for the design of orbital cryogenic refueling systems.