Dual-Membrane Gas Trap for the Space Station Freedom Internal Thermal Control System 932162

A gas trap is being developed for use in the internal thermal control system (ITCS) of Space Station Freedom. The function of the gas trap is to remove and vent noncondensed gases (NCG) that may be entrained in the ITCS water loop. Noncondensed gas bubbles in excessive concentrations can cause the performance of the centrifugal pump to degrade, block coolant flow in remote components, and cause inaccuracies in instrumentation readings.

A design has been created utilizing polypropylene hydrophobic and nylon hydrophilic membranes. The hydrophobic membrane allows gas transfer from the water/gas mixture across the membrane to ambient, and blocks liquid flow at the expected ITCS pressure levels. The hydrophilic membrane permits ITCS water to flow through the membrane, and blocks noncondensed gas at the expected water pressure differential. The water leaving the hydrophilic membrane is degassed and exits from the gas trap. The gas trap orbital replacement unit (ORU) design weighs 10.5 lb, has a water pressure drop of 2.5 psid at a flow rate of 3000 lb/hr, and will meet water leakage requirements at system pressures of 85 psig. Subscale tests of the final configuration have shown essentially complete removal of air NCG at concentrations up to 10 percent by volume at a 3000-lb/hr water flow rate and up to 20 percent by volume at a 1230-lb/hr water flow rate.

This paper describes the pump sensitivity tests, gas trap trade study, membrane selection process, development testing, and evolution of the gas trap membrane module. The final gas trap design is nearing completion, and the latest test results are presented in this paper.