Simulation of Heat and Mass Transfer in Direct Contact Membranedistillation (md): The Effect of Membrane Pore Space Description

Abstract

Abstract The concept of pore space inter–connectivity in a porous membrane is very essential and cannot be ignored in any realistic attempts to simulate mass and energy flux in membrane distillation (MD) processes. In this study, a Monte Carlo (MC) simulation model is developed to describe mass flux and related transport properties of interest in MD processes. This model is a three dimensional network model, it is designed to be comprehensive and free of adjustable parameters, and therefore, it can be applied to all MD processes regardless of their different physical setups. It takes into consideration the effects of employed membrane physical properties, pore level vapor flux transport mechanism(s), transport at the membrane boundaries (process dynamics), and temperature polarization phenomenon. To illustrate the influence of membrane pore space representation, direct contact membrane distillation process (DCMD) was chosen to be simulated among several MD models. A comparison of MC simulation model predictions, one when membrane pore space is described by a three–dimensional network model of inter–connected bonds and sites, and the other when it is described by the classical capillary tube model, show that DCMD process vapor flux and transport properties are significantly reduced when membrane pore space is described the capillary tube model. The only case when the MC simulation model predictions are in agreement regardless of membrane pore space model employed, is when membrane pore sizes are assumed to be of uniform radius, pore level vapor flux is linearly related to the pressure drop across the pore (Knudsen diffusion), and the temperature polarization phenomenon can be neglected, i.e., the three dimensional network model is practically functioning as a capillary tube model.