Numerical study of head-on collisions between two glass microsphere droplets

The collision of molten glass microsphere droplets represents a fundamental phenomenon in spheronization, yet a comprehensive understanding of this process remains elusive. A numerical simulation is conducted to investigate the head-on collision dynamics of two molten glass microsphere droplets at varying Weber numbers, by integrating the level set and volume of fluid methods. Three distinct collision regimes are identified: merging, separation into satellite-free droplets, and separation leading to the formation of satellite droplets. Furthermore, the critical Weber numbers delineating the different regimes are presented. Examination of axial and radial variations in the droplets reveals the existence of five distinct states spanning the three collision regimes. The distribution of external vortices around the droplets directly influences the outcomes of droplet collisions. High-pressure regions and high-pressure liquid bridges within droplets serve as key factors in determining the merging or separation of the droplets. Region of high pressure at the end of the liquid bridge acts as a critical indicator for distinguishing between collision separations with and without satellite droplet generation. Observations of velocity and pressure distributions in separations that produce satellite droplets are consistent with the end pinch-off mechanism. This study holds significant implications for controlling high sphericity during the spheronization of glass microsphere droplets.