Global model of crossflow microfiltration based on hydrodynamic particle diffusion

Abstract

A global model of crossflow microfiltration is presented which predicts filtration flux and concentrated particle layer thickness as they vary along the axial coordinate of a crossflow microfilter under steady or quasi-steady operation. The model incorporates the concepts of shear-induced hydrodynamic diffusion of particles and the transport along the membrane surface of a fluid-like concentrated particle layer whose viscosity is a function of particle volume fraction. Conditions for which a stagnant layer of packed particles exists beneath a flowing layer are also described. This particle layer may impart a hydraulic resistance to flow of permeate which is modeled by standard filtration theory. The particle volume fraction and the suspension velocity within the flowing layer are predicted as they vary with both distance from the membrane surface and with distance from the channel entrance. The effects of shear rate, transmembrane pressure drop, particle size and other quantities on the permeate flux are discussed.