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Description:
This thesis presents numerical methods, software, and simulations of multiphase flows with bubbles at various scales based on the volume-of-fluid approach. The applications originate from the goal of developing a numerical model of electrochemical reactors for water electrolysis. Conventional reactors use a proton-exchange membrane to separate the products. Membrane-less reactors, investigated in this work, instead rely on the flow of electrolyte that carries away the generated bubbles. Currently, electrochemical production of hydrogen is superseded by cheaper production from fossil fuels. This justifies research aimed at the reduction of the cost and exploring newer designs of electrolyzers. A major component of the model describes flows with bubbles including the effects of surface tension. The first part of the thesis presents a hybrid particle volume-of-fluid method for curvature estimation that is more accurate at lower resolutions than standard techniques. The method is applied to various cases of bubble coalescence, air entrainment, and bubbles in vortical flows. The second part is devoted to flows with bubbles that do not coalesce. Surfactants stabilize the liquid films between bubbles so they can collide or create a stable structure known as foam. A standard approach to describe such cases introduces a separate volume fraction field for each bubble making the cost proportional to the number of bubbles in the simulation. The multilayer volume-of-fluid method is introduced to overcome this challenge. The demonstrated applications include the generation of foam in microfluidic devices and breaking waves. Finally, the developed methods are applied to flows in electrolyzers. The simulations of bubble dynamics in electrolyzers supported by experimental data have helped to gain understanding of the physical mechanisms governing their operation. Components describing the relevant electrochemical phenomena are then combined in a multiscale model that represents small bubbles nucleated on the electrodes as ...