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Active TRL 5 (started at 4, targeting 9)
Robust and reliable condensing heat exchangers (CHX) are needed to control temperature and humidity in the cabin which ensures human health and comfort and maintains electrical/mechanical equipment. Over time, system degradation caused by contamination can result in a compromised ability to collect moisture. Microbial growth on the surface can result in a risk to crew health. Both can cause problems for downstream equipment as well as maintaining the environment. A system that is robust against contaminants and microbial growth is required to minimize hardware replacement mass and limit operations required to maintain/replace the hardware.
The existing state-of-the art CHX on ISS is subject to degradation over time via the conversion of the coating from hydrophilic to hydrophobic. The process of rejuvenating a used and failed heat exchanger is extremely expensive and time-consuming, and data from ISS may be showing that a single rejuvenation event is all that can be expected over time, making long-term reuse undesirable.
The CHX project was initiated in order to demonstrate the use of an upgraded CHX on ISS in a legacy Common Cabin Air Assembly (CCAA) Heat Exchanger ORU in the integrated, relevant environment on ISS. CHX will be operated on ISS for as long as the system performs its intended function.
An Additively Manufactured Condensing Heat Exchanger (AMCHX) is being manufactured with an upgraded coating to demonstrate better performance and longevity. Using additive manufacturing techniques will reduce cost and manufacturing time for subsequent units.
The project has encountered several issues with metal powder and fusion of weld layers. The AMCHX is expected to be launched to ISS in 2028.
This effort includes the following via a contract with Collins Aerospace: building/flying a flight demo of an improved hydrophobic heat exchanger coating which is more resistant to siloxanes and microbial growth, enabling dormancy and limiting the production of dimethylsilanediol (DMSD) which affects water processor hardware life. The new CHX is smaller from a volumetric standpoint, and additive manufacturing is expected be quicker/less expensive in future once the process and print files are proven.
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