Exploiting Capillary Sorbent Films for Air Revitalization aboard Spacecraft: Analysis of a Semi-Passive CO2 Scrubber
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Liquid sorbents have provided a primary means for robust carbon dioxide (CO2) control aboard submarines for decades. Unfortunately, such systems have not been adopted for use aboard spacecraft due to the fact that fine droplet sprays, thin falling films, and buoyancy-driven bubbly flows are not easily managed in the essentially gravity-free environments of orbiting spacecraft. Such applied engineering challenges have remained outstanding for the microgravity fluid physics community. As a work-around, in this research, a stable, silent capillary-driven ‘thin film’ is produced over a massively parallel network of open channels for both CO2 uptake and degas functions in a microgravity environment. Following several quantified assumptions, simple analytical models of species, heat, mass, and momentum transport are invoked providing clear design guides for a future engineering demonstration of the approach aboard the International Space Station. For critical sorbent properties such as CO2 capacity, effective diffusion rate, and concentration- and temperature-dependent viscosity, we provide the essential requirements of flow rate, size, shape, stability, power draw, and other aspects of the system. The results imply that a considerable reduction in system mass and volume is possible for the liquid sorbent approach for CO2 scrubbing when compared to the current state of the art.