The prediction of flux decline in cross-flow microfilters via three-dimensional fluid dynamic models of tortuous pore structure
Cross-flow microfiltration is a viable method to increase the in-use lifetime of semi-synthetic metalworking fluids. However in operation, fouling of the microfilter has been shown to occur and bring about a reduction of microfilter flux. This research develops a fluid dynamic model of the tortuous pore geometry to simulate the progression of fouling and investigate the associated effect on flux decline. A three-dimensional tortuous pore geometry was created to study the development of fouling mechanisms via a fluid dynamic model. The geometry was obtained by reconstructing a three-dimensional geometry from images of two-dimensional cross-sectional slices of a α-alumina microfilter obtained from a focused ion beam. A wall collision model and a particle trapping model were developed for the investigation of fouling mechanisms in three dimensions. Hydrodynamic, particle-particle electrostatic, and Brownian forces as well as the wall collision model and particle trapping model were used in the reconstructed geometry via computational fluid dynamics to simulate metalworking colloidal particles traveling through and becoming trapped in the tortuous pore paths of a microfilter. Results revealed sharp flux decline initiating from partial pore blocking and subdued flux decline transitioning to cake layer development with steady-state flow. This flux behavior was consistent with experimental flux data. The fluid dynamic model was enhanced with particle-membrane electrostatic forces. The addition of such forces via Surface Element Integration was shown to affect particle trajectories in a tortuous three-dimensional microfilter membrane geometry. The model was validated by comparing experimental flux decline data with simulation flux decline data. A design of experiments was conducted to investigate the effects of transmembrane pressure, particle-membrane (PM) zeta potential, and particle-particle (PP) zeta potential on flux decline. The simulation experiments revealed that low flux decline was associated with relatively low transmembrane pressures and near-zero values of PP- and PM-zeta potential; and relatively high transmembrane pressures and more-negative values of PP- and PM-zeta potential. The amount of flux decline was shown to be correlated to the specific nature of partial and complete pore blocking in the pore structure.
membrane microfiltration, three-dimensional simulation, semi-synthetic, metalworking fluids, microfiltration, fluid dynamic model, flux decline, electrostatics
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign