NASA's challenging deep space exploration missions demand innovative, reliable, and cost-effective technologies for life support systems. Air revitalization, particularly CO2 removal, in this manner, is a key life support system. However, the legacy solid sorbent (zeolite)-based CO2 removal technology used in the ISS experiences reliability issues and capability gaps. One of the alternative technologies under consideration is CO2 deposition. Recent NASA studies demonstrated that utilizing cryogenic coolers offers cold surfaces for CO2 capture (deposition) and can be an effective approach to revitalize cabin air. Nevertheless, to maintain purity to feed to a downstream Sabatier reactor, and to ensure high efficiency of CO2 capture, humidity from cabin air must be removed prior to CO2 deposition on cold surfaces. The current ISS dehumidification system employs solid desiccants (silica gels) and has maintenance and high energy consumption challenges. 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 work aims to utilize a unique 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/re-humidification. Such a subsystem employs a cold and hot VPS to serve as the absorber and desorber portions of the process system, produces temperature gradient by a heater and a chiller, as well as a regenerative heat exchanger, and uses two pumps for liquid desiccant recirculation. Therefore, the subsystem can continuously operate to dehumidify /re-humidify cabin air and regenerate desiccant. This paper describes design and development efforts of the VPS-based spacecraft cabin air dehumidification/re-humidification prototype that utilizes a selected regenerable liquid desiccant (ionic liquid EMIMESO4), and indicates the potential of this humidity control subsystem for implementation as part of an alternative spacecraft CO2 removal system.
Byanjankar et al. (Sun,) studied this question.