CFD modeling of porous membranes

Membrane filtration has become firmly established as a primary technology for ensuring the purity, safety and efficiency of treatment of water or effluents. Water desalination is one of the major applications of this technology around the world. Several researches have been performed to develop and design membrane systems in order to increase the process accuracy and performance. In this research, the laminar fluid flow in porous tubes, a mode of crossflow filtration tubular membrane, is simulated numerically using the computational fluid dynamics (CFD) techniques. A two-dimensional numerical solution of the coupled Navier–Stokes, Darcy’s law and mass transfer equation has been developed using control volume based finite difference method. Case study was performed for a microfiltration process. Prediction of the growth rate of the concentration polarization boundary layer along the length of tubular membranes has been performed. Effects of various operating conditions (e.g. geometrical dimension, required membrane surface area, Reynolds number and fouling) on the performance of membrane are studied and some comments on designing of such membranes are suggested.

In the present work, the effects of different operating conditions on the concentration polarization layer have been studied. This has done with developing a numerical finite volume code, using SIMPLE algorithm, for solution of flow and concentration fields. A two-dimensional microfiltration membrane with permeable walls in cylindrical system was considered as the case study. The developed numerical model successfully predicts the fundamental mechanisms involved in flux decline behavior during crossflow filtration. The axial concentration profiles present the important influence of the membrane length which is a very important factor in designing a microfiltration crossflow membrane. The concentration polarization under a wide range of operating conditions has been analyzed in terms of the concentration boundary layer thickness. These numerical results show that a higher axial Reynolds number leads to a decrease of the thickness of the local concentration boundary layer and that a higher Schmidt number leads to a decrease of the thickness of the local concentration boundary layer. It is generally accepted that approaching to turbulent conditions can improve the performance of the membrane.