Effect of interface deformation on hydrodynamics of liquid-liquid two-phase flow in a confined microchannel

Effect of interface deformation on flow patterns, recirculation flow, vorticity magnitude, and liquid film thickness of liquid-liquid two-phase flow in a confined microchannel was investigated via a simulation method using the VOF-CSF model. The quantitative control over the droplet interface deformation is achieved by systematically studying the influences of diameter ratio, viscosity ratio, continuous phase flow rate as well as interfacial tension coefficient, and further, the corresponding interface deformation mechanisms are comprehensively revealed based on the force field characteristics. Especially, two typical flow field structures inside the droplet are clarified to quantitatively distinguish the liquid-liquid two-phase flow patterns, namely slug and plug flow, and the transition law of flow field structure is also investigated. The slug flow is characterized by two vortices inside the droplet and the dominant forces are the differential pressure force and shearing force. However, in plug flow, two additional secondary recirculating vortices are observed, in which the Laplace pressure force plays a significant role. Moreover, it is also found that the vorticity magnitude is positively correlated with the interface deformation coefficient. Taking multiple variables with a wide range into account, a universal correlation model for predicting the liquid film thickness with several dimensionless numbers is established. Finally, the obtained results could provide theoretical guidance for designing a liquid-liquid two-phase flow microsystem to enhance heat and mass transfer and reaction process.