Microporous Hydrophobic Hollow Fiber Modules for Gas-Liquid Phase Separation in Microgravity

Gas-liquid interphase mass transfer operations, such as gas-liquid phase separation, gas absorption into liquid or dissolved gas separation from liquid, gas humidification and drying via liquid contact, and evaporative cooling are readily accomplished on the Earth with settling/spray chambers, packed towers, or bubble columns. The inability of these gravity-dependent phase contact and/or separation devices to function in microgravity has almost completely precluded the use of gas-liquid mass transfer as a available unit operation in spacecraft and spacesuit fluid processing systems. Recent advances in hollow fiber membrane performance have made this technology suitable for gas-liquid mass transfer operations in microgravity, in which the walls of many small hollow fibers provide very high volume-specific-surface-area for fluid phase separation or contact without gravity dependence or phase intermixing. This paper reports on gas-water mass transfer tests performed utilizing microporous hydrophobic Hollow Fiber Modules (HFMs) of the type currently employed as blood oxygenators in heart-lung machines. In these HFMs, gases are transferred to and from water or other hydrophilic liquids through the microporous fiber walls; liquid water does not enter the pores of the highly hydrophobic wall material. The experiments included air-water phase separation, absorption of oxygen and carbon dioxide into water and separation of these dissolved gases from water, air humidification and drying by contact with temperature-controlled water, and controlled evaporation of water into vacuum. In each of these experiments, a small, light HFM successfully performed the mass transfer function, with no leakage of liquid water through the porous walls of the hollow fibers, even with high pressure across the fiber walls for extended periods of time. These results demonstrate that gas-liquid mass transfer unit operations on hydrophilic liquids, implemented with microporous hydrophobic HFM technology, are ready for use in microgravity fluid processing systems.