The Dynamics of Massively Parallel Open Capillary Channel Systems for Direct-Contact Liquid Sorbent Applications in Spacecraft Life Support

Direct contact liquid-gas sorbent beds offer unique benefits for spacecraft air quality control. In a recent ISS technology demonstration experiment (CSELS—Capillary Sorbent), two 16-parallel channel wedge capillary contactors plumbed in series demonstrated passive ‘thin film’ control, modelling both absorption and desorption functions for a potential low-g gas scrubbing system for spacecraft. The open wedge channels mimic terrestrial falling film reactors by exploiting capillary pressure gradients instead of gravity. A fully functional, though scaled, CO2 scrubber system is under consideration for technology demonstration on short schedule aboard ISS. In this presentation we highlight the fluid mechanics of the process. We identify the limits of operation, stability, and transients for systems as functions of wedge geometry and working fluid thermophysical properties. Rare exact solutions are found which may be applied to enormous systems of n parallel channels. The analytical approach serves as the building block for massively parallel systems requiring large surface areas for transport. Such compact high liquid surface area systems may find value in that poorer performing lower toxicity working fluids may still trade well against other more toxic chemical approaches.