Testing of a Spray‐Bar Thermodynamic Vent System in Liquid Nitrogen Available to Purchase

To support development of a microgravity pressure control capability for liquid oxygen (LO₂), Thermodynamic Vent System (TVS) testing was conducted at Marshall Space Flight Center (MSFC) using liquid nitrogen (LN₂) as an LO₂ simulant. The spray‐bar TVS hardware used was originally designed by The Boeing Company for testing in liquid hydrogen (LH₂). With this concept, a small portion of the tank fluid is passed through a Joule‐Thomson (J‐T) device, and then through a longitudinal spray‐bar mixer/heat exchanger in order to cool the bulk fluid. To accommodate the larger mass flow rates associated with LN₂, the TVS hardware was modified by replacing the recirculation pump with an LN₂ compatible pump and replacing the J‐T valve. The primary advantage of the spray‐bar configuration is that tank pressure control can be achieved independent of liquid and vapor location, enhancing the applicability of ground test data to microgravity conditions. Performance testing revealed that the spray‐bar TVS was effective in controlling tank pressure within a 6.8‐kPa band for fill levels of approximately 90%, 50%, and 25%. Tests were also conducted with gaseous helium (GHe) in the ullage. The TVS operated satisfactorily with GHe in the ullage. However, the total cycle duration increase ranged from 14% to 28% compared to similar tests with gaseous nitrogen (GN₂). Testing demonstrated that the spray‐bar TVS design was flexible enough for use in two different propellants with minimal hardware modifications.