MIGRATION AND DEPOSITION OF SUBMICRON PARTICLES IN CROSS-FLOW MICROFILTRATION

The migration and deposition of submicron particles in laminar crossfl ow microfiltration is simulated by integrating the Langevin equation. The effects of operating conditions on the particle trajectories are d iscussed. It is found that the Brownian motion of particles plays an i mportant role in particle migration under a smaller crossflow velocity of suspension or a smaller filtration rate. Based on the simulated tr ajectories of particles, the transported flux of particles arriving at the membrane surface can be estimated. The particle flux increases wi th an increase of filtration rate and with a decrease of particle diam eter; however, the effect of crossflow velocity on the particle flux i s not obvious. The forces exerted on particles are analyzed to estimat e the probability of particle deposition on the membrane surface. The probability of particle deposition increases with an increase of filtr ation rate, with a decrease of crossflow velocity, with a decrease of particle diameter, or with an increase of zeta potential on the partic le surfaces. The simulated results of packing structures of particles on the membrane surface at the initial stage of filtration show that a looser packing can be found under a larger crossflow velocity, a smal ler filtration rate, or a smaller diameter of filtered particles. Cros sflow microfiltration experiments are carried out to demonstrate the r eliability of the proposed theory. The deviation between the predicted and experimental data of filtration rate at the initial period of fil tration is less than 10% when the Reynolds number of the suspension fl ow ranges from 100 to 500.