The Rise of Taylor Bubbles in Vertical Pipes

Elongated bubbles which are constrained by the walls of a pipe are commonly known as Taylor bubbles. Taylor bubbles are prevalent in industrial gas-liquid flow, where they are commonly found in buoyancy driven fermenters, the production and transportation of hydrocarbons in the oil and gas industry, the boiling and condensing process in thermal power plants, and the emergency cooling of nuclear reactors. These bubbles also exist in the natural world, and are the driving force behind certain types of volcanic eruption. An analysis of the literature identified a paucity of experimental or numerical studies investigating the rise of Taylor bubbles in pipes with a diameter in excess of 0.12 m or in pipes which contain a change in geometry. The aim of this thesis was to gain a better understanding of the behaviour of Taylor bubbles in flow conditions which have not previously been studied. To achieve this, a CFD model was used to simulate the rise of single Taylor bubbles and a set of experiments conducted. The CFD model was validated against the results of published experimental studies, empirical correlations and theoretical predictions. Further validation was conducted using the results of the experimental study which investigated the rise of Taylor bubbles in a pipe of diameter 0.29 m. These experiments confirmed that the theoretically predicted stability and rise rate of the bubble were correct. Bubbles were also shown to exhibit oscillatory behaviour. Sets of parametric simulations replicated the behaviour observed in the experiments and predicted by theoretical models for a wide range of conditions. The qualitative and quantitative experimental behaviour of a Taylor bubble rising through an expansion in pipe geometry was replicated by the CFD model. Bubbles of sufficient length were observed split as they rose through the expansion in diameter, which produced pressure oscillations. The effects of a variation in a number of parameters, including the angle of expansion, the ratio of the upper to lower pipe diameters and the liquid viscosity, were explored.