Experimental evaluation of the performance of a thermodynamic vent system for a vapor-liquid storage tank with R141b as the testing fluid

Controlling the pressure of a propellant tank while minimizing the propellant mass loss is the primary technical demand of cryogen storage missions in the reduced gravity environment in space. Thermodynamic vent system (TVS) has been considered as a potential solution for this issue. Before conducting studies on TVS-equipped cryogen storage technology in space and on the ground, a TVS unit at room temperature with refrigerant R141b as the substituting phase-changing fluid was designed and tested. The performance of the TVS was evaluated at different combinations of the operation parameters including the fill level (35%, 50%, 65%), heat load (74.7 W, 108.8 W, 148.4 W), and control strategies. Mass loss, which is an unavoidable result of tank pressure control, was quantitatively compared between the TVS method and the direct gas vent method over a given period of time. Taking the heat load of 74.7 W as an example, the results showed that the mass loss can be reduced by as much as 79.3%. Assuming the vented stream contains 40% mass fraction of liquid if vented directly at zero-gravity, TVS can not only control the tank pressure within a designated range but also significantly help to reduce the mass loss.