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The Effect of Membrane Deflections on Flow Rate in Crossflow Air-to-Air Exchangers

Manufacturing of air-to-air heat and moisture crossflow exchangers can result in membrane surfaces with significant deflections due to moderate pressure differences across the membrane under normal operating conditions. This paper presents a methodology for the determination of membrane deflections for two types of support systems. Both initial slack and pre-stressed membranes are considered. Experimental data for two types of membrane are presented, which confirms the theoretical model of membrane elastic deflections. It is shown for fully developed laminar flow in crossflow exchangers that significant flow differences will occur in the supply and exhaust flow channels for the same pressure drop across the exchanger. It is concluded that these crossflow exchangers should be manufactured with pre-stressed membranes, and a good support scheme should be chosen to minimize the effect of membrane deflections on the exchanger performance.