Liquid-liquid emulsions will undergo a phase inversion, in which the dispersed phase becomes the continuous phase and vice versa, under certain conditions. A phase inversion is not a smooth transition and an emulsion close to the inversion point may oscillate back and forth between the oil-in-water (O/W) and water-in-oil (W/O) forms, creating flow instabilities that may be detrimental in certain industrial situations. The results of laboratory laminar flow experiments in which an aqueous and an organic liquid phase are emulsified as they flow through a circular tube containing a commercial high-shear static mixer are discussed. As the concentration of the dispersed phase and/or its flow rate is increased, flow instabilities are initiated in the test-section and are measured as fluctuations in pressure drop. The intensity of these fluctuations reaches a maximum as the liquid-liquid system approaches the phase inversion point. Once a stable phase inversion is achieved, the fluctuations subside. This phenomenon was observed over a wide range of viscosity ratios for the two liquid phases, but was absent for low viscosity ratios and low-shear static mixers.
Observations Regarding the Nature of Oil-Water Phase Inversion and Instability in Laminar Flow Through Circular Tubes Containing Static Mixers
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Sood, A, Cheluget, E, & Karnik, U. "Observations Regarding the Nature of Oil-Water Phase Inversion and Instability in Laminar Flow Through Circular Tubes Containing Static Mixers." Proceedings of the ASME 2005 Fluids Engineering Division Summer Meeting. Volume 2: Fora. Houston, Texas, USA. June 19–23, 2005. pp. 181-186. ASME. https://doi.org/10.1115/FEDSM2005-77438
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