Numerical Simulation of Droplet Formation in Microfluidic T-Junction Devices

The T-junction geometry has been widely used for producing monodisperse droplets in microfluidic devices. Droplet formation regimes and sizes are expected to depend on a variety of conditions including fluid flow properties and geometrical parameters. Experiments have investigated drop production in a narrow control parameter space and developed analytical models for specific operating regimes. We take advantage of numerical simulations based on volume-of-fluid method to explore this broad parameter space systematically, and contrast our results with prior experimental data. We find our simulations predict well different regimes of drop formation. We also observe that our drop size data is in good agreement with three different experimental reports. Although our results match experimental data, the analytical models do not agree with each other since they are based on specific operating conditions. We use numerical simulations to elucidate the missing components in the physics of drop formation at a T-junction. Furthermore, we investigate how the size of droplets is changed when the viscosity ratio of the two phases is varied. In this case, we find that higher dispersed phase viscosity leads to larger drop size. Building on previous models, an analytical expression is suggested to account for the effect of drop viscosity on drop size.