Three-dimensional numerical simulation of droplet formation in a microfluidic flow-focusing device

Three-dimensional numerical simulation is performed to study the formation mechanism and influencing factors of droplets in a microfluidic flow-focusing device (MFFD). Three types of liquid-liquid two-phase flow patterns include squeezing, dripping and jetting. Through the level-set method, the two-phase interface is tracked and the process of droplet generation is obtained. The key factors influencing droplet formation size and frequency are studied in MFFD. The results show that the formation of droplets is divided into three stages: Filling stage, Necking stage and Detachment stage, respectively. The formation of droplets is mainly that the continuous phase has flow-focusing effect on the dispersed phase. The flow rate ratio of two phases, the viscosity of the continuous phase and interfacial tension between two phases are the key factors that influence droplet size and frequency. As the flow rate ratio increases, the droplet size becomes larger and the frequency decreases. As the viscosity of the continuous phase increases, the size of the droplets becomes smaller and the frequency increases. When the two-phase interfacial tension becomes larger, the size of the droplets becomes larger and the frequency decreases.