The work presented in this dissertation provides a novel technique of manipulation of colloidal entities during membrane filtration based on an AC electrokinetic phenomenon called dielectrophoresis. First, the influence of dielectrophoretic (DEP) forces created on a membrane surface to levitate colloidal particles is studied both theoretically and experimentally. A numerical model based on the convection-diffusion-migration equation is presented to calculate the concentration distribution of colloidal particles in shear flow under the influence of a repulsive DEP force field. The simulation results indicate that particle accumulation on the membrane (or membrane fouling) during filtration can be averted by creating a repulsive DEP force field on the membrane surface. Corresponding experimental study employs a microelectrode array on a glass surface in a tangential flow cell, to apply repulsive DEP forces on polystyrene particles suspended in an aqueous medium. Applying a non-uniform AC electric field on the microelectrodes generates the DEP force field that levitates the polystyrene particles above the surface. This study indicates that the repulsive dielectrophoretic forces imparted on the particles suspended in the feed can be employed to effectively mitigate membrane fouling in a crossflow membrane filtration process.
The second phase of the study is aimed at controlling colloid transport through a microporous membrane using DEP forces acting across the pores. A theoretical analysis of colloid transport through straight cylindrical capillaries in the presence of a non-uniform AC electric field is developed. Numerical simulations demonstrate that the interaction of the particles with the electric field generates strong repulsive DEP forces, acting selectively on the colloidal particles to control particle transport through the pore. A combination of DEP forces and size exclusion in porous material is proposed to develop an energy efficient technique for colloid filtration. Experimental results on this steric-dielectrophoretic filtration are also obtained using novel ``sandwich membranes" and colloidal suspensions in a dead-end filtration system. The primary advantage of this steric-dielectrophoretic mechanism is that the filtration can be achieved by filter media (such as membranes) that have considerably larger pore sizes than the retained colloids. The technique can also result in tunable filtration mechanisms, where particles with same size but different electrical properties can be separated using suitably designed membranes. / Fluid mechanics, Electrokinetic filtration
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.10048/483 |
| Date | 11 1900 |
| Creators | Molla, Shahnawaz Hossain |
| Contributors | Subir Bhattacharjee (Mechanical Engineering), Lianfa Song (Texas Tech), Ken Cadien (Chemical Engineering), Robert Koch (Mechanical Engineering), Mike Lipsett (Mechanical Engineering), David Nobes (Mechanical Engineering) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 5229578 bytes, application/pdf |
| Relation | Molla and Bhattaccharjee (2005), Molla and Bhattaccharjee (2007), Molla and Bhattaccharjee (2008) |
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