Effect of Geometry on Droplet Formation in a Microfluidic Flow-Focusing Device

Abstract

Droplet formation in a microfluidic flow-focusing device studied using two different simulation techniques has been presented. The lattice Boltzmann method is found to be computationally faster as compared to the volume-of-fluid method to model a flow focusing device. Also, volume-of-fluid modeling required constant monitoring of residual as very high spurious velocities are developed at the interface, which requires the time step be reduced to satisfy the CFL condition. Subsequently, the lattice Boltzmann method was employed to study the effect of geometry of a microfluidic flow focusing device on droplet formation. Orifice width, orifice length and distance of the orifice from the inlet were varied for different Capillary numbers. It was observed that for a fixed geometry, droplet size decreases as the Capillary number is increased. The droplet size increases on increasing orifice width and on increasing the distance of orifice from the inlet. On increasing the orifice length, the droplet size first decreases to a minimum and then starts to increase to reach an asymptotic value, which depends on the flow parameters and geometry.