Hydrodynamics of liquid-liquid two-phase flow accounting for the coupling of dean vortices and Poiseuille flow

Abstract

Hydrodynamics of liquid–liquid (L-L) two-phase flow in a confined helical microchannel are investigated via a VOF-CSF model, and further the influences of continuous phase flowrate, interfacial tension, viscosity ratio, helical screw pitch, helical radius as well as the diameter ratio of droplet to channel were systematically ascertained. To achieve the precise control over the interface deformation in a confined helical microchannel, the correlation equations with several key dimensionless numbers are established to predict the droplet aspect ratio, eccentricity and the minimum liquid film thickness. Especially, the minimum film thickness can be used to distinguish the flow field structures, and when the dimensionless outer minimum liquid film thickness (δ*out) is greater than 0.16, there is only one complete vortex system structure inside the droplet. Otherwise, two vortices are observed. Besides, the Q-criterion is used to quantitatively confirm the disappearance of vortices inside the droplet. Finally, the force field characteristics are also discussed to reveal the corresponding droplet interface deformation mechanisms, and it is found that, the droplet is driven forward by the differential pressure force, and deformed by the shear force along its flow direction. Both of the Dean force and Coriolis force usually control the interface deformation of droplet in the radial direction. The results in our study offer valuable guidance for designing the L-L two-phase flow microsystems to realize the goal of process intensification.