Research on the binary droplet collision of coalescence, separation and breakup processes of water in oil emulsions based on fluid dynamics

This study investigates the complex physical phenomenon of binary droplet collisions, focusing on the effect of the Weber number (We) on collision outcomes. A series of binary droplet collision models were established for varying We, and the critical We ranges for droplet coalescence, separation, and breakup were determined. The results indicate that the critical We for coalescence and separation is around 248, while the critical We for separation and breakup is approximately 1200. Specifically, when We≤247, the colliding droplets coalesce; for 249 ≤ We≤1199, separation occurs; and for We≥1201, the droplets break up after collision. Expressions for the critical Weber numbers for coalescence–separation (We₁) and separation–breakup (We₂) were derived. Additionally, nomograms were developed to illustrate the effects of Reynolds (Re) and Ohnesorge (Oh) numbers on collision outcomes. As Oh and Re increase, the coalescence region narrows, while the breakup region expands. Furthermore, with increasing Oh, the critical Re position gradually decreases, with a progressively smoother rate of decrease.