Numerical study and controlled generation of double emulsion droplet in a six-way junction microfluidic device using design of experiment method

This study uses numerical simulations based on the Volume of Fluid-Continuum Surface Force (VOF-CSF) method to investigate the controlled generation of double emulsion droplets in a six-way junction microfluidic device. Using Design of Experiments (DOE) and Response Surface Methodology (RSM) in a flow-focusing microfluidic device, the simultaneous effects of important parameters, including the inner phase capillary number and phase flow rates, on the double emulsion characteristics, including droplet size, shell thickness, frequency of compound droplet generation, and monodispersity are investigated for the first time. According to our findings, the most significant parameter determining the double emulsion characteristics is the outer phase flow rate. Multi-core double emulsion droplets are also generated when the inner phase capillary number and middle phase flow rate increases and outer phase flow rate decreases. Additionally, we show that the monodispersity of the double emulsion under the dripping and jetting flow patterns is acceptable for most of the applications within the range of input parameters. This research develops beyond conventional droplet generation techniques by identifying the optimal flow combinations and providing quantitative equations for precisely predicting and controlling double emulsion characteristics based on the simultaneous effects of input parameters. Additionally, the proposed model enables it possible to generate multiple double emulsions with a wide range of shell thicknesses and different numbers of internal drops. The findings provide an innovative approach for designing microfluidic systems that have been successfully used in the double emulsions generation, especially in complicated encapsulation systems and for the food and pharmaceutical industries.