Breakup and coalescence behaviors of oil droplets in complex swirling flow system

Droplet migration, coalescence, and breakup are common phenomena in cyclone systems. This study explores and provides insights into the breakup and coalescence behaviors of droplet groups in a swirling flow field through a combination of theoretical analyses and numerical simulations. A cylindrical cyclone with a tangential inlet was used to construct a stable swirling flow field, which was then comprehensively studied. The swirl intensity initially increased and then started decreasing, and the internal and external swirls coexisted. The breakup and coalescence behaviors of oil droplets in a complex swirling flow field were simulated, and their coalescence mode and breakup region were investigated in detail. Based on the energy-dissipation rate of the turbulence, the swirl-flow field was divided into strong- and weak-dissipation regions comprising overflow, separation, and underflow. Sauter mean diameter and energy-dissipation rate were evident in these: the overflow part exhibited a linear relationship, the separation part exhibited a quadratic linear relationship, the underflow part remained stable under low Reynolds numbers, and a quadratic linear relationship was observed at high Reynolds numbers. Based on the critical Weber number of droplets, a factor "g" is proposed to predict the droplet size, which has an exponential relationship with the Reynolds number.