Analysis on the nonuniformity of cake formation in rotating-disk dynamic microfiltration

Abstract

Abstract This study analyzes the nonuniformity of cake formation and filtration flux in rotating-disk dynamic microfiltration of fine particles. Because the installation of a rotating disk in the filter chamber generates high shear stresses on the membrane surface, a rotating-disk filter can be used to achieve light cake mass and high filtration flux. The effects of operating conditions—such as disk rotation speed and transmembrane pressure—on the filtration flux, membrane fouling, and cake properties are discussed both experimentally and theoretically. Because the shear stresses generated by a rotating disk are not uniformly distributed on the membrane surface, the cake formations as well as the filtration flux are functions of position and rotating-disk structure. In this study, the distributions of fluid velocity and shear stress on the membrane surface were simulated using computational fluid dynamics. Combined with experimental data concerning local cake properties, such as thickness, porosity, and specific filtration resistance, the mechanism of cake formation based on a force balance model was analyzed. The result shows that the local filtration flux increases in tandem with critical particle size. The agreement between the calculated results and the experimental data demonstrates the reliability of the proposed method. The relationship between local filtration flux, critical particle size, and operation conditions can be expressed as a nonlinear equation. This method estimates the local cake mass and filtration rate, not only for optimizing operating conditions to achieve the best filtration performance but also for designing high-efficiency disk structures or filter modules.