Lattice Boltzmann simulation of droplet formation in microchannels under an electric field

Abstract

The intermolecular potential model of the lattice Boltzmann method (LBM) is used to simulate the effect of an imposed electric field on droplet formation process from mixing of immiscible fluid streams in a 2D microchannel with non-wetting walls. The electrodes are placed near the inlet of the main channel where droplet breakup occurs. Simulation results show that droplet size decreases and formation frequency increases as the intensity of the electric field is increased. This is because the gap between the emerging droplet and main channel wall is decreased under the action of the electric field during the droplet formation process, which induces the emerging droplet to block the continuous phase more effectively. The obstruction increases the pressure difference across the droplet interface, leading to stronger squeezing effects on the neck of the droplet. For a fixed velocity ratio of the continuous phase to the disperse phase, there exists a critical value of electric field intensity for which the droplet begins to touch the surfaces of the electrodes. At this critical value of electric field intensity, the droplet size suddenly decreases and droplet formation frequency suddenly increases drastically. At high electric field intensity when the electric force dominates the flow field, deformation of droplet is relatively independent of the velocity of the continuous phase. Simulation results show that an electric field can be used to control droplet size and droplet formation frequency effectively.