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A unique Liquid Carry Over Sensor (LCOS) is being developed as part of the condensing heat exchanger and filter assembly (CHXFA). The CHXFA is used in the Environmental Control and Life Support System (ECLSS) of the Columbus Orbital Facility (COF), the European Module of the International Space Station (ISS). The LCOS is designed to monitor the performance of the condensing heat exchanger assembly and the COF air-water separator by detecting water within 2 mm of the sensor element surface. The sensor has been designed to fit flush with duct wall, with no intrusion into the air flow. The sensor surface has a fused glass finish with very low porosity and near zero water retention, and is able to detect extremely small levels of moisture. The LCOS design is based on a capacitive technology which is largely insensitive to contaminants, unlike competitive resistive technologies, thereby ensuring maintenance free, long lifetime performance which is a requirement of all ISS applications.

Condensing heat exchangers (CHX) are used in space life support systems to control cabin temperature and humidity. Humidity control is provided by cooling the air below its dew point and separating the condensed water from the gas flow. To achieve efficient air/condensate separation in the absence of gravitational forces, a hydrophilic coating is added to the air flow passages of the heat exchanger and a slurping section is added to the air outlet. It is necessary to monitor the air exiting the CHX to verify that condensate droplets are not carried over with the air flow. For short missions, it is possible to use intrusive structures to catch the carried over moisture and direct it to a measurement cell where the overall accumulation can be detected. However, for long-term missions, such as those proposed for the International Space Station (ISS), the impact of contamination, both as dust and microbial species, dramatically reduces the attractiveness of an intrusive sensor.