Testing of Commercial Hollow Fiber Membranes for Spacesuit Water Membrane Evaporator

Three commercial off-the-shelf hollow fiber membrane evaporators, which were modified for low pressure, were tested as potential spacesuit water membrane evaporator (SWME) heat rejection technologies at pressures below 33 pascals in a vacuum chamber. Water quality was controlled in a series of 25 tests, first by simulating potable water that was reclaimed from wastewater and then by changing periodically to simulate the ever-concentrating make-up of the circulating coolant over that which is predicted over the course of 100 extravehicular activities. Two of the systems, which are comprised of nonporous tubes with hydrophilic molecular channels as the water vapor transport mechanism, were severely impacted by increasing concentrations of cations in the water. One of the systems, which was based on hydrophobic porous polypropylene tubes, was not affected by the degrading water quality or the presence of microbes. The polypropylene system, the SWME 1, was selected for further testing. An inverse flow configuration was also tested with SWME 1, with vacuum exposure on the inside of the tubes providing only 20% of the performance of the standard configuration. SWME 1 was also modified to block 50% and 90% of the central tube layers, and was tested to investigate performance efficiency. Performance curves were also developed in backpressure regulation tests; these revealed important design considerations arising from the fully closed valve. SWME 1 was shown to be insensitive to air bubbles that were injected into the coolant loop. Development and testing of a full-scale prototype that is based on this technology is in progress.