A liquid–liquid slug flow regime is generated when two immiscible liquids are pumped into a channel at varying flow rates. However, the addition of a second immiscible phase is accompanied by an increase in pressure drop relative to the single phase flow case. The focus of this work is to experimentally investigate the pressure drop associated with a liquid–liquid slug flow regime and in particular to examine the effects of slug length, slug numbers and continuous phase on the pressure drop in a hard walled FEP Teflon circular capillary of 1.59mm inner diameter. The flow was analysed over the dimensionless Reynolds and Capillary number ranges of 0.68–97.63 and 0.000045–0.06 respectively by employing four different carrier fluids; Pd5, Dodecane, FC40 and AR20 with water as the dispersed phase. Experiments involved varying the dimensionless water slug length between 1.05–11.01 and the dimensionless oil slug length between 0.71–14.14. Results show a large increase in pressure drop for such flows compared to single phase values. A comparison between the experimental data and correlations in the literature highlights the lack of flow physics in their composition. An alternative approach is presented that can be used for predictive purposes to estimate the interfacial contribution to the total pressure drop in a liquid–liquid slug flow regime.

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