CFD study and experimental verification of droplet formation characteristics in a flow-focusing microfluidic device

This study numerically investigates droplet formation in a three-dimensional flow-focusing microchannel and validates the results with a lithographically fabricated device (error $<4\%$ ). The effects of injection angle, continuous phase viscosity, flow velocities, and interfacial tension on two-phase flow regimes, instantaneous flow fields, droplet size, formation frequency, and breakup time were examined. At acute angles, increasing the injection angle delays droplet detachment, producing larger droplets with greater interdroplet distance. At obtuse angles, larger injection angles slow down droplet formation and produce smaller droplets with shorter spacing. The injection angle of $\theta =90°$ yields the maximum droplet diameter. As the flow rate ratio increases, the influence of the injection angle decreases, whereas higher capillary numbers amplify its effect. Higher continuous phase viscosity and velocity accelerate droplet formation, producing smaller droplets, while higher dispersed phase velocity and interfacial tension delay detachment, yielding larger droplets. Repeatability tests (coefficient of variation $<1\%$ ) confirm high stability and reliability. These findings provide practical guidelines for designing controlled droplet generation in microfluidic applications.