A Thin Film Liquid Sorbent Reactor for CO2 Scrubbing Aboard Spacecraft
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For decades, direct contact liquid-gas CO2 sorbent beds have functioned successfully aboard confined crewed vehicles (i.e., submarines). Despite the unique challenges of microgravity fluids management, such approaches also offer attractive benefits for spacecraft air quality control. In a recent ISS technology demonstration experiment (CSELS—Capillary Sorbent), two 16-parallel open capillary channel contactors plumbed in series demonstrated passive ‘thin film’ control, modeling both absorption and desorption functions for a potential low-gravity CO2 scrubbing system for spacecraft. The open wedge-shaped channels mimic terrestrial falling film reactors by exploiting capillary pressure gradients instead of gravity. In this paper, we highlight the fluid mechanics of the process with and without the effects of CO2 absorption across the surface. The dramatic changes in fluid properties due to CO2 absorption in the contactor and temperature rise in the degasser are addressed via approximate analytic and numerical solutions to the species, energy, and momentum transport equations. We identify the limits of operation, stability, and transients for systems as functions of wedge geometry and working fluid thermo-physical properties. Analytical solutions are found that may be applied to systems of n-parallel channels. The analytical approach serves as the building blocks for massively parallel systems requiring large surface areas to achieve the desired performance.