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Multiple Phase Flows

Multiple phase flows are often encountered in industrial systems. By definition, they are flowfields which involve more than single phase of fluid, such as gas-liquid or solid-gas flowfield. Oil-particle separators, vapor condensation, pump cavitation, inkjet droplet formation, trapped air pockets in fluid, and engine fuel sprays are good examples of multi-phase flows. Because of the complex physics of multiple phase flows, CFD has become an integral part of understanding and designing multiple phase flow systems.

To analyze a multi-phase flow, the first step is to decide whether it should be modeled using a homogeneous or inhomogeneous multi-phase flow model. The homogeneous model assumes the fluids of different phases possess the same field solutions in pressure, temperature, velocity, etc. It is best to apply the homogeneous model to multi-phase flow with a clear distinction between the different phases, such as free surface flows. The inhomogeneous model, on the other hand, solves individual sets of equation for each phase, and can be applied to all multi-phase flow situations. Although it provides a more accurate solution, the inhomogeneous model requires longer computational time.

The figure above demonstrates a multi-phase flow analysis for bubble column simulation. In this analysis, small air bubbles are injected into a water chamber through a port near the bottom surface. The size and distribution of the air bubbles can be specified. Air bubbles rise and disperse in the water chamber due to the interactions between buoyancy, surface tension, pressure, flowfield velocity, and turbulent dispersion. Each representative group of bubbles is tracked throughout the analysis to provide location and trajectory of the bubble, and its momentum exchange with the mean flow.