Prediction of particle deposition and layer growth in the preparation of a dynamic membrane with cross-flow microfiltration

Abstract

Theoretical and experimental investigations were conducted to predict particle deposition and layer growth during formation of a dynamic membrane using cross-flow microfiltration. A critical particle size model was developed and solved in radial, circumferential and axial directions by analyzing the forces acting on a single particle. The model accounted for the normal drag, lateral lift, shear-induced and Brownian diffusion forces in the depositional direction, the van der Waals force in the circumferential direction, and the cross-flow drag and van der Waals forces in the axial direction. Cross-flow velocity and feed temperature were selected as representative influencing factors to examine variations of the critical particle sizes with permeate flux. Experiments were then conducted with carbon tubes as the support and zirconium dioxide particles as the coating material to verify the model. Results showed that a dynamic layer with non-uniform thickness along the circumferential direction was formed within the horizontal tube due to gravity. The layer thickness decreased as the cross-flow velocities were increased under a given trans-membrane pressure difference and feed concentration. An appropriately large cross-flow velocity was beneficial to achieve thickness uniformity during formation. The effect of the feed temperature on the critical particle size and layer thickness can be ignored. Comparisons between the theoretical predictions and experimental data of the layer thicknesses displayed good agreements. The effects of trans-membrane pressure differences and feed concentrations were finally examined in the present work.