Testing of Vortex Phase Separator-Based Spacecraft Cabin Air Dehumidifier/Rehumidifier Unit for CO2 Removal Using Regenerable Ionic Liquid Desiccant

NASA’s challenging deep-space, long-duration exploration missions demand innovative, reliable, and cost-effective technologies for life support systems. A promising CO2 removal technology, CO2 Deposition System, utilizes cryogenic coolers to attain cold surfaces for CO2 capture and offers effective cabin air revitalization. Nevertheless, to maintain product purity for downstream Sabatier processing and ensure highly efficient CO2 capture, humidity from cabin air must be removed prior to CO2 deposition on cold surfaces. Currently, the primary CO2 removal system aboard the ISS employs solid desiccants (silica gels) for air dehumidification, which present challenges related to maintenance and energy consumption. A liquid desiccant can instead be utilized to build a humidity control subsystem as part of a CO2 deposition system and enhance its performance. This study investigates a novel Vortex Phase Separator (VPS)-based air-desiccant contactor design that can achieve a direct-contact, high-efficiency heat and mass exchange between air and desiccant, and offer reliable, high-throughput operation for dehumidification/rehumidification. When a subsystem is configured with two VPSs—a cold VPS and a hot VPS—functioning as the absorber and desorber within the process system, it can continuously dehumidify/rehumidify cabin air. This experimental effort focused on testing VPS-based spacecraft cabin air dehumidifier/rehumidifier unit for a CO2 removal system. The setup included one VPS, used ionic liquid (IL) 1-Ethyl-3-methylimidazolium ethyl sulfate [EMIM][ESO4] as a regenerable liquid desiccant, and operated either as a dehumidifier using cold IL, or as a rehumidifier using hot IL. The tests aimed to evaluate the effects of air flow rate (9.4- 28.3 l/min), IL flow rate (1.0-2.0 l/min), and IL temperature (15.4-57.8oC), on dehumidification/rehumidification performance. Overall, despite the use of highly saturated IL, the system achieved dehumidification and rehumidification ratios of up to 51.7% and 84.6%, respectively, demonstrating the viability of the VPS-based humidity control subsystem for integration into a next-generation spacecraft CO₂ removal system.