Bubble motion, deformation, and breakup in stirred tanks

This thesis presents numerical and experimental studies on bubble motion, deformation and breakup in turbulence, which is a commonly encountered topic in industry. The numerical work was performed with a novel technique: the lattice-Boltzmann method (LBM), and the experimental work was carried out in a laboratory-scale stirred tank.; The simulations indicate that bubble breakup in turbulence is basically a force balance mechanism. The breakage occurs when the bubble Weber number reaches a critical value. This breakage results from the interaction between the deformed bubble and the nearby eddies with about the same size as the bubble. The breakup process is somewhat stochastic; it occurs when the velocity field around the bubble is pushing the neck and pulling the end.; The experimental results for bubble breakup show good agreement with the simulations. Surfactants have different effects on bubble breakup, depending on the size of the surfactant molecule. Inside the stirred tank, strong turbulence is concentrated in the impeller outflow region. The majority of the bubble breakup occurs in the strong turbulence region.; A computer code based on the LBM was developed and parallelized for both two-dimensional and three-dimensional multiphase flows. The code could be easily adapted to other applications. The LBM is a very useful computational fluid dynamic (CFD) tool for simulating complex flows.