| The research described in this dissertation focuses on the analysis and optimization of mixing in two industrially-relevant mixing devices that are currently employed for laminar to transitional flow applications: the impinging jet contactor and the roller bottle bioreactor. A full description of the fluid mechanics is obtained for each system by integrating fluid dynamics experiments and direct numerical simulations. Computational fluid dynamics simulations are used to obtain the fully-three-dimensional velocity fields in each device under laminar flow conditions, and particle image velocimetry is used to validate the velocity fields experimentally. Particle tracking algorithms are then used to characterize the velocity field in terms of Eulerian measures of mixing performance and to obtain explicit Lagrangian measures of mixing performance for each device under several operating conditions.; In the impinging jet contactor, two steady-state flow regimes are shown to exist: for jet Reynolds numbers less than ten, the jets do not impinge and the velocity field scales linearly with Reynolds number; for jet Reynolds numbers greater than 10, the jets begin to impinge and recirculation regions form above and below the impingement point. Mixing simulations show that no mixing occurs for. steady flow in a symmetric-jet contactor. However, mixing is improved substantially by slight modifications of the impinging jet geometry that disrupt geometric symmetry. To examine unsteady flows in the impinging jet, a laser-induced fluorescence (LIF) technique is developed. Using the LIF technique, optimum operating conditions are identified for two different impinging jet geometries as a function of Reynolds number.; Similar computational and experimental techniques are used to examine flow and cell settling in the roller bottle bioreactor. Results show that closed pathlines in the flow cause poor fluid mixing and inefficient cell settling. Such limitations, however, are readily overcome by introducing unsteadiness to the flow, and two transient methods are demonstrated. One method is based on a periodic reversal of bottle rotation direction, and the other involves rocking the rotating bottles. Using these two techniques, complete mixing and cell settling are shown to occur, greatly increasing the overall productivity of roller bottles. |
