Phase Inversion in Liquid-Liquid Pipe Flows

Phase inversion is the phenomenon where the continuous phase of a liquid-liquid dispersion changes to become dispersed and the dispersed becomes continuous. Phase inversion has important implications for a number of industrial applications where liquid-liquid dispersions are used, since the change in the mixture continuity affects drop size, settling characteristics, heat transfer and even the corrosion behaviour of the mixture. In pipeline flows, phase inversion is usually accompanied by a step change or a peak in pressure drop. The chapter reviews the work on phase inversion during the pipeline flow of liquid-liquid mixtures when no surfactants are present. Investigations have revealed that in pipes a transitional region occurs during inversion from one phase continuous to the other, characterized by complex flow morphologies (multiple drops, regions in the flow with different continuity) and even stratification of the two phases over a range of dispersed phase volume fractions. The observations on the phase inversion process in pipelines are discussed and the parameters which affect the phenomenon are summarized. In addition, the various models available for predicting phase inversion are analyzed, as well as the methodologies developed to account for the transitional region with the complex morphologies and the flow stratification and to predict pressure drop during inversion.