A Porous Media-Based Heat Exchanger: Experimental Measurements of Moisture Condensation

Temperature and humidity control using condensing heat exchangers in microgravity requires condensation and separation of liquid from the air stream. A layered porous media-based condensing heat exchanger where capillary suction is used to imbibe and selectively remove the condensed water from a flowing air stream provides an attractive alternative to current designs. Experiments using a porous flat-plate, consisting of top and bottom halves with cooling tubes embedded in the middle, show that a hydrophilic porous graphite substrate can condense, and imbibe moisture without forming a liquid layer on both the top and bottom parts of the condensing surface. Measured condensation and heat transfer rates for a porous graphite substrate for a range of inlet air temperature and relative humidity at atmospheric pressure are presented in this paper. Without condensate removal, dripping of the condensate does not occur under terrestrial condition until the overall saturation reaches approximately 45% in the graphite substrate. When condensate is removed at a steady rate, liquid saturation levels as high as 80% has been observed without dripping or liquid layer formation. The results from these experiments should help in the design of a passive, porous media-based condensing heat exchanger capable of gravity independent operation.