Dynamics and controllability of droplet fusion under gas–liquid–liquid three-phase flow in a microfluidic reactor

Gas–liquid–liquid three-phase flow systems have unique advantages of controlling reagent manipulation and improving reaction performance. However, there remains a lack of insight into the dynamics and controllability of water droplet fusion assisted by gas bubbles, particularly scaling laws for use in the design and operation of complex multiphase flow processes. In the present work, a microfluidic reactor with three T-junctions was employed to sequentially generate gas bubbles and then fuse two dispersed water droplets. The formation of the dispersed phase was divided into multiple stages, and the bubble/droplet size was correlated with operating parameters. The formation of the second dispersed droplet at the third T-junction was accompanied by the fusion of the two dispersed water droplets that were formed. It revealed a two-stage process (i.e. drainage and fusion) for the two droplets to fuse while becoming mature by breaking-up with the secondary water supply stream. In addition, a droplet contact model was employed to understand the influence on the process stability and uniformity of the merged/fused droplets by varying the surfactant concentration (in oil), the viscosity of the water phase, and the flow rates of different fluids. The study provides a deeper understanding of the droplet fusion characteristics on gas–liquid–liquid three-phase flow in microreactors for a wide range of applications.