Bursting at the surface: Fine droplet generation from an exploding water drop in hot oil

The explosion of a water drop near the surface of hot cooking oil may eject fine droplets into the air. Although such a process is often observed in activity in the kitchen, the formation process of these fine droplets has not been investigated extensively Kiyama et al., “Morphology of bubble dynamics and sound in heated oil,” Phys. Fluids 34, 062107 (2022). In this study, we use a high-speed camera to visualize this phenomenon, showing that the size of these droplets are of the order of 10 μm. The droplet formation process is divided into two sequential stages. The first stage, which is associated with the explosion of a submerged water drop and following rupture of the air-oil interface, largely governs the formation of fine droplets. The magnitude of the fine droplets formation seems to be related through the dimensionless relative distance from the bubble formed on the drop to the oil surface. The formation of the small droplets is driven by the Rayleigh–Taylor instability, which is similar to the fragmentation of a droplet by a laser pulse Klein et al., “Drop fragmentation by laser-pulse impact,” J. Fluid Mech. 893, A7 (2020). The second stage is associated with the splash dynamics. Liquid ligaments dispatch relatively larger droplets at later times. We also recorded sounds in the surrounding air, in which the impulsive sounds are related to rupturing of a bag, which is formed due to a sudden extension of exploded drop. The subsequent splash dynamicsalso have unique acoustic signals at a higher acoustic frequency than that of the enclosed cavity after the surface sealing. These characteristics suggests the acoustics may be useful for a better understanding of this complex fluid phenomenon including fine droplets sizes and cavity closure.