1997-07-01

Development of a Liquid Carry Over Sensor for Monitoring the Performance of Condensing Heat Exchangers 972350

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. Any proposed sensor must have a certain degree of immunity to contamination and should not present an opportunity for accumulation of contamination or enhanced microbial growth.
This paper describes the development and testing of a Liquid Carry Over Sensor (LCOS) designed for use in the Columbus Orbital Facility (COF), the European Laboratory Module of the ISS.
The LCOS is a capacitive-type sensor which has been designed to fit into the ducting wall, providing no intrusion into the airflow. The sensor surface has a fused glass finish with extremely low porosity and near zero water retention and is able to detect extremely small levels of moisture.

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