Sensitivity of the performance of a flat-plate liquid-to-air membrane energy exchanger (LAMEE) to the air and solution channel widths and flow maldistribution

Abstract Liquid-to-air membrane energy exchangers (LAMEEs) are novel energy exchangers which use semi-permeable membranes to separate air and desiccant solution streams. The semi-permeable membrane allows simultaneous heat and water vapor transfer between the air and the desiccant solution streams. These exchangers, which include bonded elastic membranes, are prone to significant variations in the flow channel widths, which causes flow maldistribution, and this causes performance degradation. This paper uses a numerical model to show the sensitivity of the steady-state performance of a flat-plate LAMEE to the air and solution channel widths, when operated as a supply air dehumidifier and a diluted desiccant solution regenerator. Simulations show that, without air flow channel width variations, the effectiveness of both the dehumidifier and the regenerator can always be increased toward 1.0 by reducing the nominal air and solution channel widths. To account for variations in the air channel widths, which occur due to construction tolerances and pressure differences across the membrane, laminar fully developed flow equations are used to investigate the influence of random variations in the air channel widths on the performance (i.e. effectiveness and air pressure drop) of the flat-plate LAMEE. The main contribution of this paper is that it shows that there exists an optimal air channel width for flat-plate LAMEEs with flow maldistribution due to random variations in the air channel width. Decreasing the air channel width below this optimal value will result in a decrease in effectiveness. It is found that the optimum nominal air channel width for flat-plate LAMEEs may be 5–6 mm and the optimum nominal solution channel width is 1–2 mm.