Numerical Simulation of Droplet Breakup, Splitting and Sorting in a Microfluidic Device

Droplet generation, splitting and sorting are investigated numerically in the framework of a VOF technique for interface tracking and a finite-volume numerical method using the commercial code FLUENT. Droplets of water-in-oil are produced by a flow focusing technique relying on the use of a microchannell equipped with an obstacle to split the droplets. The influence of several parameters potentially affecting this process is investigated parametrically towards the end of identifying "optimal" conditions for droplet breakup. Such parameters include surface tension, the capillary number and the main channel width. We show that the capillary number plays a crucial role in determining droplet properties and the efficiency of the related generation process. An obstacle configuration can be effectively used to split a droplet, with the droplets being naturally sorted at the end of the main channel. Larger values of the capillary number generally lead to an increase in the droplet frequency and a decrease in its typical size.