TRANSPORT THROUGH MICROFILTRATION MEMBRANES - PARTICLE HYDRODYNAMICS AND FLUX REDUCTION

The transport of a particle-containing liquid through a capillary pore has been studied using a finite element method. Direct calculation ha s been made of flow fields, drag correction factors, and pressure drop s for single particles and short chains of particles using the center- line approach. Three cases have been considered: a moving sphere in a stationary liquid, a stationary sphere in a moving liquid, and a movin g sphere in a moving liquid. The correction factors for the inner sphe re in short chains agree well with the results of complex stream funct ion calculations for infinite chains of particles. Two topics have bee n particularly addressed. First covered is the use of the numerical ca lculations to identify the limiting particle spacings for which single -sphere calculations give close agreement with the calculations for su ch inner spheres. It is shown that single-sphere calculations have a w ide range of applicability, considerably simplifying the effort involv ed in numerical calculation. Second, we carry out calculations up to l arge values of the particle radius/pore radius ratio. The case of a mo ving sphere in a moving liquid is directly relevant to the third topic of the paper-transport of particles through microfiltration membranes . Application of the numerical results for conditions corresponding to a commercial capillary pore microfiltration membrane show that hydrod ynamic interactions can result in the maximum achievable flux for part icle-containing fluids being significantly less than the pure water fl ux. Such hydrodynamic flux reduction has previously been neglected by membrane researchers. (C) 1994 Academic Press, Inc.