Development of a Thermal Control System Dual-Membrane Gas Trap

The Internal thermal control system (ITCS) for the International Space Station Alpha (ISSA) employs a dual-membrane gas trap to remove and vent noncondensed gases entrained in the water-cooling loop. The removal of noncondensed gas bubbles is significant because the gases impede the performance of the centrifugal pump, interfere with the coolant flow, and affect instrumentation readings. The gas trap utilizes hydrophobic and hydrophilic membrane tube pairs to vent separated gases to ambient. Bench-top tests of the current configuration have demonstrated removal of nitrogen at concentrations up to 8 percent by volume at a 3000 lbm/hr water flow rate.

Optimization studies to maximize the removal of noncondensed gases from the water-cooling loop with minimal pressure drop have been performed to determine the ideal membrane configuration. The flight test design uses one hydrophobic hollow fiber per membrane tube pair to minimize water vapor loss. In order to meet a revised system burst pressure of 150 psid, the gas trap flight design has also evolved by increasing the density of the secondary hydrophobic membrane.

This paper describes the gas trap development and presents test results of the current full-scale design. Testing consisted of steady-state nitrogen injections at varied levels and nitrogen slug tests that utilize a pressurized vessel to release bursts of nitrogen into the water stream.