A computer-aided model to simulate membrane fouling processes

A computer model based on a 2-D Voronoi tessellation is proposed to represe nt the porous structure of an asymmetric inorganic membrane and to simulate the fouling process that takes place during filtration of particle suspens ions. Voronoi tessellation has proved to be an effective tool in modeling t his kind of porous media. II consists of dividing the space into irregular convex polygonal entities (polygons in 2-D). Th, tessellation structure can be changed by imposing different constraints. on the pattern of convex pol ygons that form it, allowing to represent very close the cross section of a n inorganic membrane. Several ways to transform a tessellation in a model o f porous media have been implemented. In this study, edges between polygons are considered to be pure segments making a whole pore space embedded into a solid structure. The geometry of each pore segment is completely specifi ed by three parameters: pore body diameter, pore throat diameter and pore l ength. The first one is computed so that the pore volume fraction matches t he porosity of the clean membrane. Pore throat diameter is randomly assigne d to each pore segment from a previously specified pore size distribution. Basic fluid dynamics is used to evaluate the fluid flow along a pore segmen t in terms of its geometry and the pressure difference at its ends. These l ocal flows are used to determine total fluid flow through the membrane and its effective permeability. The filtration process of a suspension of solid particles with a given size distribution is simulated. Particles larger th an pore bodies located on the active surface cannot move into the tessellat ion (membrane) but they can produce a surface layer leading to cake formati on. Otherwise, particles small enough penetrate the tessellation (membrane) blocking an interior pore segment (the fluid flow through that segment cea ses) or reducing its size. In both cases, a reduction in the total flow bec ause of interior fouling is produced. Data are presented for membrane perme ability and flow reduction at different degrees of fouling. The effect of p ore size distribution as related to particle size on the prevalent type of fouling is considered. (C) 2001 Elsevier Science B.V. All rights reserved.