Hydrodynamics of triple emulsion droplet generation in a flow-focusing microfluidic device

A numerical research is conducted to investigate the triple emulsion droplet generation in a threedimensional axisymmetric flow-focusing device. The simulation predicts three flow regimes: dripping, jetting, and threading. The hydrodynamics underlying the droplet generation and effects of operation conditions on the droplet generation are clarified. An increase in flow rate of one dispersed phase results in the larger droplet enclosing this phase and smaller droplet enclosed by this phase. As the interfacial tension between any two phases increases or viscosity of any phases decrease, the flow regime transits from jetting to dripping, accompanied by a decrease in the droplet size. Increasing the interfacial tension coefficient or decreasing the viscosity under both two regimes can increase the droplet size. Additionally, regime diagrams for single, middle, and triple emulsion droplet generation are compared, and an empirical equation is proposed to predict the flow regime transition. (c) 2021 Elsevier Ltd. All rights reserved.