Computational studies of protein and particle transport in membrane system

Particle transport plays a critical role in many membrane systems both with respect to the filtrate flux and the overall selectivity. A number of previous studies have used particle trajectory analysis to obtain insights into the effects of particle transport on the behavior of membrane systems; however, these studies have typically been based on simplified models for the interactions often neglecting the effects of electrostatic, interparticle, and Brownian forces. The objective of this thesis was to obtain a more fundamental understanding of the behavior of membrane systems by performing detailed numerical simulations of the flow and particle trajectories as a function of the device operating conditions.;Numerical calculations were performed using the commercial software package FLUENT. The fluid streamlines were evaluated by solution of the Navier-Stokes equation, both in the presence and absence of counter-electroosmosis. Particle trajectories were evaluated by numerical integration of the Langevin equations accounting for the combined effects of electrostatic repulsion, enhanced hydrodynamic drag, Brownian diffusion, and interparticle forces.;In the absence of Brownian forces, the particles are unable to enter the pore unless the drag force on the particle associated with the filtration velocity can overcome the electrostatic repulsion between the charged particle and the charged membrane. Interparticle interactions can significantly alter the particle trajectories, allowing particles to overcome the energy barrier and thus reducing the critical flux for particle transmission. Brownian forces allow particles to enter the pore even when the magnitude of the electrostatic repulsion is greater than the hydrodynamic drag, with the particle transmission increasing with increasing filtration velocity. Counter-electroosmosis has a relatively small effect on the fluid streamlines and particle trajectories if simulations are performed at a constant filtrate flux; simulations at constant pressure show a significant difference due to the reduction in filtrate flux associated with the induced streaming potential. Simulations were also performed to evaluate the possible effects of transmembrane pressure pulsing, although un-realistically rapid pulsing was required to have a significant effect on the critical flux.;These results provide important insights into the nature of particle motion in membrane systems, and they provide a framework for future analyses of particle trajectories, critical flux, and particle transmission in both microfiltration and ultrafiltration.