Thermal and environmental control systems for future exploration spacecraft must meet challenging requirements for efficient operation and conservation of resources. Regenerative carbon dioxide (CO_2) removal systems are attractive for these missions because they do not use consumable CO_2 absorbers. However, these systems also absorb water vapor that may be vented to space along with CO_2, or may consume significant power to return the water to cabin air. This paper describes an innovative device designed to minimize water absorbed in regenerative CO_2 control systems. Design studies and proof-of-concept testing have shown the feasibility of a compact, efficient membrane water vapor exchanger (WVX) that will conserve water while meeting challenging requirements for operation on future spacecraft. Compared to conventional WVX designs, the innovative membrane WVX described here has the potential for high water recovery efficiency, compact size, and very low pressure losses. The key innovation is a WVX core design that maintains highly uniform flow channels built from water-permeable membranes. The proof-of-concept WVX incorporates all the key design features of a prototypical unit at a reduced scale (1/23 relative to a unit sized for a crew of six). The proof-of-concept WVX achieved over 90% water recovery efficiency in a compact core, in good agreement with analysis models. Furthermore the overall pressure drop is very small (less than 0.5 in. water, total for both flow streams) and meets requirements for service in environmental control and life support systems on future spacecraft. These results show that the WVX provides uniform flow through flow channels for both the humid and dry streams. Measurements also show that CO_2 diffusion through the water-permeable membranes will have negligible effect on the CO_2 partial pressure in the spacecraft atmosphere.
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