Development of a Hydrodynamic Technique for Rapid Concentration of Dilute Suspensions

In this thesis, we develop a hydrodynamic technique for the rapid concentration of dilute suspensions using the inertial secondary flow in the rotating parallel plate system. The major purpose of this thesis is the improvement of bioparticle detection by accelerating the sample preconcentration process. Current techniques such as centrifugation, filtration, dielectrophoresis, and immunomagnetic separation are time consuming and have sample volume limitations. The mechanism we employ is the shear induced secondary flow produced in the rotating upper plate and stationary lower plate system. This flow field has been well established by a regular perturbation expansion (e.g., Mellor, et al., 1967). We couple this flow to the particle motion model of a rough sphere interacting with a smooth plane (King & Leighton 1997). The model was tested experimentally and showed good agreement with no adjustable parameters. In addition to studies of the unmodified parallel-plate geometry, we also examined a modified geometry produced by adding triangular bumps at the bottom plate to accelerate inward particle migration. We investigate the interaction between particles and this bump geometry through both experiment and the simulation results. While the bumps were found to accelerate inward migration, they also imposed limitations on allowable rotation rates which prevented an overall improvement in concentration under some conditions. We conclude by identifying the scaling laws necessary for further design improvement.