Numerical evaluation of the effects of asymmetric membrane heat conductivity and moisture adsorption hysteresis on the performance of air-to-air membrane enthalpy exchanger

Abstract

Effects of tangential heat conduction and moisture adsorption hysteresis of the membrane on the heat recovery performance of cross-flow and counter-flow membrane enthalpy exchangers are investigated numerically. The accuracy of the numerical simulation model is evaluated by predicting an experimental case and a reasonable accuracy is achieved. It is found that the temperature profile at the membrane surface is significantly influenced by the tangential heat conduction in the membrane. The variation of temperature profile at the membrane surface results in variations of the convective heat resistance and the sensible heat effectiveness. Simulation results demonstrate that the sensible heat effectiveness firstly increases and then decreases with the increasing membrane heat conductivity. The optimal membrane heat conductivity is about 0.1 ∼ 1 W m−1 K−1. Two types of the moisture adsorption hysteresis are assumed and expressed by simple expressions. It is found that the moisture adsorption hysteresis decreases the moisture diffusion flux across the membrane and accordingly decreases the latent heat effectiveness obviously for both counter-flow and cross-flow patterns. Current results indicate that membranes with large heat conductivity are not beneficial for sensible heat recovery and membranes with small adsorption hysteresis are beneficial for latent heat recovery.