Modeling and CFD Simulation of Membrane Flow Process

Abstract

In the processing industries several membrane technologies are used to separate and concentrate various fluid stream where the concentrate or/filtrate has high value products. Nevertheless, pore blocking is one of the major factors determining the applicability, efficiency and performance of the membrane filtration and separation system. Inside and outside membrane pore blockage leads to concentration polarization and cake buildup that reduces the flux rate and increases losses in system efficiency. Several experimental and theoretical works exist that describe the pore flow and blocking process. However, a limited amount of published work integrates the pore blocking with computational fluid dynamics (CFD). The change in the fluid stream and membrane characteristics during the process are the major challenges in CFD modeling. This paper presents the initial simulations of two-dimensional CFD models that directly model the actual micro pore flow and the porous medium flow (Darcy flow). Various pressure and pore sizes (porosity and permeability) were simulated. For the first model, pore flow model, simplified two-dimensional micro pores were modeled and the continuity and Navier-Stokes equations were solved in all regions including pores. Appling various inlet pressures, the velocity and pressure in all fluid regions are simulated. In second model, the membrane region is modeled as porous medium and the flow field is simulated by using porous medium characteristics. The porous medium characteristics, porosity and permeability, were estimated from pore flow average outlet velocity. The result indicates that both models with equivalent values can be used to predict the overall flow fields. However, both models have to overcome challenges to be widely used. With the direct pore flow (pores flow) simulation, mesh generation becomes a challenge since the membrane pores are very small as compared to the inlet and outlet regions. The pore flow simulation results indicate that CFD can be used to understand the membrane flow characteristics and fluid mechanics. It also can be used to design and / or select a membrane system. For the simulation of membrane as porous medium, the detail of flow through the porous medium including the inlet and outlet effects becomes obscured. However, the system overall performance can be simulated using CFD model for porous medium.