Doctor of Philosophy (PhD)
Liquid-liquid segmented flows in a square microchannel are investigated numerically using a hybrid front-tracking/front-capturing method. The code is found to be well-adapted to a large range of flow parameters, but droplet flows are limited by poor accuracy at Laplace number above 100 – 1000 and plug flows are limited by the code’s current inability to adequately model the flow in thin films at low capillary numbers. A Schwarz-Aitken acceleration technique is investigated as a means to reduce computation time, but is found not to be advantageous compared to the parallel multigrid formulation of the code. Numerical simulations are divided into pressure-driven flows in a stationary channel and flows in a rotating channel, which may be driven by a combination of pressure gradients and centrifugal effects. A large set of parametric studies is run for pressure-driven flows of droplets and thick-film plugs. Pressure loss for these flows is shown to be predicted to within 13% by a single-phase model, with more precise predictions requiring knowledge of the droplet or plug volume and frequency. In rotationally-driven plug flows, both the plug mobility and the pressure drop are shown to be highly influenced by the buoyancy of the plug induced by the apparent centrifugal acceleration. High buoyancy, or large Eötvös numbers, can even reverse the slope of the plug mobility-capillary number relation and result in total bypass flow at low capillary numbers. Meanwhile, Coriolis acceleration is shown to cause the plugs to drift to an off-centre equilibrium position in the channel. This drift is typically small and proportional to the angular speed of the channel, but both the magnitude and, surprisingly, the direction of the drift depend on the Reynolds number of the flow. Further research is recommended to further quantify and explain these phenomena.
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Walker, Eamonn Daire, "Numerical Studies of Liquid-Liquid Segmented Flows in Square Microchannels Using a Front-Tracking Algorithm" (2015). LSU Doctoral Dissertations. 3923.
Nikitopoulos, Dimitris E.