Mechanistic Models to Simulate Slug Flow in Horizontal and Vertical Pipes

Abstract

While numerous studies have been conducted on using the one-dimensional, two-fluid model to simulate a range of flow regimes in horizontal and nearly horizontal pipes, no work has been conducted thus far on using the model to simulate intermittent flow in vertical pipes, specifically in the slug flow regime where large gas bubbles are separated by rising liquid slugs.

This thesis presents the development of the model to accurately simulate this flow regime. For the first time, it has been shown that the model can capture the underlying physics behind slug generation in vertical flow: that of a falling liquid film leading to a bridging of the pipe, thereby resulting in the formation of slugs.

Closure relations for the interfacial shear force are proposed, tested and developed, where it was found that the choice of model used in the flow development region has a significant effect on the flow downstream. A new correlation has been developed that is able to accurately reproduce results and trends seen experimentally. The effects of the viscous diffusion term, a pressure loss model at the slug front and the surface tension term, all previously introduced into the model, were tested for the vertical flow cases. The effects of mesh size and the influence of the inlet boundary conditions on the characteristics of the generated slugs were also investigated.

As well as the vertical slug flow work, the thesis also presents results obtained in testing the models capabilities to simulate two other effects found in two-phase flows in pipes. The first is the hysteresis phenomena found in horizontal pipes, where the point of transition from stratified flow to slug flow and vice versa is found to shift depending on the starting flow regime. The second is terrain-induced slugging, where bends in the pipe can cause a localised build-up of liquid, causing undesired fluctuations in flow rates and pressures at the pipe outlet.