Development of a numerical methodology for the simulation of active-pressurization of cryogenic tanks

In this study, a numerical methodology, which is suitable to describe the main thermo-fluid-dynamics phenomena characterizing the active-pressurization inside cryogenic tanks, is proposed. This task is carried out comparing the numerical predictions obtained with several models with experimental results, retrieved from the literature, of a ground-based active-pressurization experiment of a liquid nitrogen (N₂) tank pressurized with high temperature gaseous N₂. The tank is modeled as 2D axisymmetric, and the solution of the heat conduction through the tank wall is coupled to the fluid-dynamic solution by means of a conjugate heat transfer model. The two-phase fluid interface is tracked using the Volume-of-Fluid (VOF) method, and the phase transition is calculated with the Lee model. Temperature varying thermophysical properties are considered for the vapor and the wall, given the wide operational temperature range. The proposed methodology allows to accurately reproduce both the pressure rise rate during gas injection and the pressure drop occurring after the end of gas injection. Finally, the results show that the introduction of a turbulence model is necessary to describe, with higher fidelity, the active-pressurization phase and that, among the tested models, the SST $k-\omega$ with low-Reynolds corrections is the most adequate to represent the pressure decrease occurring after the end of gas injection.