| This thesis describes an experimental and theoretical investigation of electric-field-induced particle segregation in concentrated suspensions of particles having different electrical properties from that of the suspending fluid. When such a suspension is subjected to a spatially nonuniform electric field, the particles migrate toward the region of high- or low-field, depending on the relative polarization of the suspending fluid and the particles. This phenomenon, known as dielectrophoresis, finds numerous applications in processes involving the collection/trapping, selective filtration and manipulation of individual particles.; We begin by briefly summarizing the theory of the dielectrophoretic force in Chapter 1. In Chapter 2, we present the experimental setup and the suspension physical properties along with a brief description of the various instruments and the methods being employed for the measurement of the various suspension properties. Chapter 3 is devoted to the description of the theoretical model for non-dilute suspensions.; In Chapter 4, we present an experimental study demonstrating the influence of a relatively weak, rotating gravity force on the field-induced particle interactions in a "clinostat" using a positively polarized suspension of heavy particles.; In Chapter 5, we study the behavior of concentrated suspensions (c initial∼5--15%), comprised of neutrally buoyant, negatively polarized particles, subject to a spatially non-uniform electric field. We find that, following the field exposure, the suspension undergoes a field induced phase transition in which the particles concentrate in the low field region. The process was modeled using an electrohydrodyanamic model, developed by Khusid and Acrivos. In chapter 6, we analyze the electrohydrodynamic model in the special case when, via a similarity transformation, the model equations reduce to ordinary differential equations for the particle concentration. Chapter 7 is devoted to an experimental study of the particle aggregation in neutrally buoyant suspensions subject to a spatially uniform ac electric field in which a new, and hitherto unexplained, pattern formation has been observed. |
