Performance investigation of liquid-to-air membrane energy exchanger under low solution/air heat capacity rates ratio conditions

Abstract

Liquid-to-air membrane energy exchanger is a novel membrane base energy exchanger, which allows both heat and moisture transfer between air and a salt solution. The heat and mass transfer performance of a single one is significantly dependent on two dimensionless parameters: number of heat transfer units and the ratio of heat capacity rates between solution flow and air flow (Cr*). The performance of liquid-to-air membrane energy exchanger under high Cr* (i.e. Cr* ≥ 1) has been comprehensively investigated experimentally and numerically in previous research. In this study, the effectiveness of a small-scale liquid-to-air membrane energy exchanger under low Cr* conditions (i.e. Cr* < 1) is experimentally tested. Good agreement between the experimental and numerical results is achieved under low Cr* cases. Practical application: The ideal energy exchanger is one that can transfer both heat and moisture because during hot and humid conditions such an exchanger is capable of transferring up to four times as much energy as an exchanger that can transfer sensible heat only. It is beneficial if the exchanger can transfer heat and moisture also between remote supply and exhaust airstreams, as this may minimize the ducting required and reduces contaminant transfer from one airstream to the other. This is very important for applications such as hospitals, laboratories, and manufacturing facilities, where slight cross contamination can cause serious health effects.