A Cryogenic CO2 Scrubber with an Integrated Switchable Heat Pipe

Human missions to explore Moon, Mars, and beyond will require reliable, compact air revitalization systems. Using a cryogenic separation system to sublimate CO2 in the processed air steam and thus remove it from the air flow is a very attractive approach for long-duration missions because it eliminates the need for consumable adsorption systems. The required cryocooling power to achieve the target CO2 removal rate for a spacecraft with four crewmembers is quite high, more than tens of Watts below 125 K. A critical need for this technology is a cryogenic CO2 scrubber with an integrated heat transport mechanism to efficiently transfer heat to a remotely located active or passive cooler during the collection phase, and to thermally disconnect from the cooler during the regeneration phase to eliminate the need for two separate cryocoolers. To meet this need, we are developing a CO2 scrubber with a built-in cryogenic liquid trap switchable heat pipe to connect the scrubber with a cooler. The scrubber has enhanced heat transfer surfaces to collect CO2 snow. The enhanced surfaces are directly cooled by evaporation of heat pipe working fluid, instead of relying on thermal conduction cooling to minimize temperature gradients on the enhanced surfaces. The enhanced surfaces also have features to promote a uniform air flow and minimize impact of channel clogging as CO2 accumulates. The design of the scrubber and switchable heat pipe is built on JPL’s experience in additive manufacturing of two-phase thermal devices with porous media. This paper discusses the design of the scrubber and the switchable heat pipe, as well as the test setup and preliminary test data for the proof-of-concept switchable heat pipe.