CFD Simulation of Droplet Formation in Microchannels by a Modified Level Set Method

A level set method embedded in a Computational Fluidic Dynamics (CFD) simulation is a useful approach in the study of microfluidic two-phase flow. In this work, we established a new governing equation for the level set function to overcome the mass loss problem. The feasibility of the modified method was proved by the simulation of a droplet formation in a co-tube microchannel. The modified method was then used to simulate the droplet flow in a focusing shape microchannel. The simulation results showed that the droplet size would decrease with an increase in the continuous phase flow rate. In the early stage of the droplet formation process, there was strong inner circulation flow that enhanced the mass transfer between the two phases and generated a concentration notch at the head of the droplet. In the later stage of the droplet formation process, the droplet moving velocity became higher, and there was no longer inner circulation flow in the droplet. The mass transfer speed slowed, and there was an enrichment of the material at the head of the droplet. The total mass transfer ratio in the droplet formation process reached 50%. The simulation results were consistent with both our previous experiment results and the results reported in the literature, which further proved the feasibility of the modified method.