Multiphase Flow Dynamics of Droplet Formation and Mixing Enhancement in Microfluidic Channel

Abstract

Interactions between multiphase fluids at the micro level in miniature fluidic systems constitute fundamental processes. Various fundamental processes have been recently investigated, leading to the discovery of optimized system configurations and appropriate operating parameters. The study of droplet formation represents one such multiphase interaction, resulting in the production of emulsions. This work explores droplet breakup dynamic and pinch-off for the two-phase flow through a microfluidic T-channel. The level set method (LSM) method has been utilized for the simulation in a microchannel. Based on the evolution of the interface, the droplet formation stages are classified as filling, necking, and pinch-off. This study underlines that the interfacial tension and density of the dispersed phase are dominating parameters in determining the pinch-off stage. We also put forth an analytical and numerical explanation to address the underlying cause of such a short period of pinch off-stage. The unsteady energy equation is solved during the pinch-off stage to provide a complete understanding of the pinch-off phenomena. Analytical relation for pinch-off time is a novel approach for interpreting its dependence on the physical variable. We have analyzed the pressure field, velocity fields, pinch-off time, and interface shape during the necking and pinching to affirm our understanding of pinch-off dynamics. In another study, we investigated the internal flow dynamics of droplet formation in the flow-focusing channel. An experiment has been performed using the μ − PIV and flow visualization techniques. The interaction of two immiscible fluids, De-aerated water, and Silicon oil, is used. The flow characteristics of the dispersed phase, the velocity fields, contour plots of vorticity (ωz), swirl strength (λ1), and circulation strength (Γ⁄UdW) have been investigated. The vortex flow region is identified during the droplet formation in such flow conditions (Re ~ 1 and Ca < 0.01). Our experimental methodology and results have illustrated the presence of a temporal vortex pair during droplet formation in the dispersed phase. Moreover, the flow characteristics have been interplayed by changing the geometry investigated.