TANK PRESSURE CONTROL EXPERIMENT: RESULTS OF THREE SPACE FLIGHTS

The Tank Pressure Control Experiment is a microgravity fluid management technology project that has accomplished three successful tests aboard the Space Shuttle. A refrigerant simulated the fluid dynamics and thermodynamics of cryogenic fluids subjected to small heat fluxes in microgravity while allowing video photography. The overall objective was to demonstrate the effectiveness of a low-velocity axial jet at mixing the fluid and thereby controlling its pressure. Pressure increases were induced with heaters, simulating in-space storage of a cryogenic fluid, and a recirculating jet mixer was operated to return the fluid to thermal equilibrium. Pressure control was found to be effective and repeatable at both high and low fluid fill levels, over a wide range of jet velocities, with varying amounts of noncondensibl e gases in the ullage, and with a variety of liquid/vapor orientations, acceleration environments, and heat inputs. Photography showed that the jet penetrated the ullage when its Weber number (momentum, or thrust, divided by surface tension) was greater than approximately 1.5, but effective pressure control was also observed without ullage penetration. Pressure spikes caused by explosive boiling were sometimes observed during heating at low heat fluxes, and these were shown to be controllable with gentle mixing.