TESTING THE EFFECTS OF HELIUM PRESSURANT ON THERMODYNAMIC VENT SYSTEM PERFORMANCE WITH LIQUID HYDROGEN Free

In support of the development of a micro-gravity pressure control capability for liquid hydrogen, testing was conducted at the Marshall Space Flight Center (MSFC) with the Multipurpose Hydrogen Test Bed (MHTB) to evaluate the effects of helium pressurant on the performance of a spray-bar thermodynamic vent system (TVS). The testing, with an ambient heat leak of about 70 W and tank fill levels of 90, 50, and 25%, was performed for 14 days during August and September 2005. The TVS successfully controlled the tank pressure within a $±3.45 kPa$ band with various gaseous helium (GHe) masses in the ullage. Relative to pressure control with an “all hydrogen” ullage, the GHe presence resulted in 37 to 68% longer pressure reduction cycle durations, depending on the fill level, during the mixing/venting phase of the control cycle. Testing was also conducted to evaluate thermodynamic venting without the recirculation pump operating, at a very low fill level. Although ullage stratification was present, the ullage pressure was successfully controlled without the pump. It was evident that the spray-bar and heat exchanger configuration, which extended almost the entire length of the tank, enabled significant thermal energy removal from the ullage even without the pump operating.