Numerical model of a small-scale liquid-to-air membrane energy exchanger: Parametric study of membrane resistance and air side convective heat transfer coefficient

A small-scale single-panel liquid-to-air membrane energy exchanger (LAMEE) is a novel membrane based energy exchanger that allows heat and moisture transfer between a supply air stream and a salt solution flow through a semi-permeable membrane. In this paper, the steady-state effectiveness of the small-scale single-panel LAMEE is experimentally measured and numerically modeled. The numerical model is compared with the experimental data for summer and winter test conditions. Parameters those are investigated using the numerical model include membrane vapor diffusion resistance (VDR) and air side convective heat transfer coefficient. The membrane VDR in the small-scale LAMEE is measured and the effect of this parameter is studied for the steady-state effectiveness. Decreasing the membrane VDR from 56 s/m to 24 s/m increases the LAMEE latent effectiveness by 11%, and as expected, it doesn't have any effect on the LAMEE sensible effectiveness. Enhanced convective heat transfer coefficient in the air flow of the small-scale LAMEE is calculated, and the effect of this parameter on the LAMEE effectiveness is investigated. The results show 138% improvement in the convective heat transfer coefficient in the air channel of the LAMEE with an air screen at Re-air = 1570 which results in 11% improvement in the LAMEE effectiveness. Finally, the modified numerical model is validated by the experimental data for the steady-state effectiveness of the small-scale LAMEE under summer test conditions at four different values of the thermal capacity ratio (Cr* = 1, 3, 5 and 7) and NTU = 3.8. Moreover, the numerical model is used for winter test conditions, and the results are compared with the experimental data. The results show that the numerical model agrees with the experimental data for the latent and total effectiveness of the LAMEE under the air heating and humidifying and air heating and dehumidifying test conditions. (C) 2013 Elsevier Ltd. All rights reserved.