Lattice Boltzmann simulation of droplet behaviour in microfluidic devices

Abstract

We developed a lattice Boltzmann model to investigate the droplet dynamics in microfluidic devices. In our model, a stress-free boundary condition was proposed to conserve the total mass of flow system and improve the numerical stability for flows with low Reynolds number. The model was extensively validated by the benchmark cases including the Laplace's law, the static contact angles at solid surface, and the droplet deformation and breakup under simple shear flow. We applied our model to study the effects of the Pelcect number, the Capillary number and wettability on droplet formation. The results showed that the Peclet number has little effect on droplet size though it slightly affects the time of droplet formation. In the creeping flow regime, the Capillary number plays a dominating role in the droplet generation process. Wettability of fluids affects the position of droplet detachment, the droplet shape and size, and its impact becomes more significant when the Capillary number decreases. We also found that the hydrophobic surface generally can produce smaller droplet.