Cavitation near a liquid-liquid interface is a well-known and an important phenomenon owing to the wide application of cavitation bubbles in emulsion preparation, wastewater treatment, petroleum refining, and other processes. However, very few studies have been conducted to observe bubble dynamics near a liquid‐liquid interface, and the interaction between a bubble and the liquid-liquid interface of oil films and water has not been considered in the literature. To gain a better understanding of bubble dynamics and offer an effective way to improve cavitation techniques, this study investigates the dynamics of a cavitation bubble near an oil film‐water interface.
Dimethyl silicone oil and deionized water are utilized to produce an oil film-water interface, and the pulsed laser-induced method is applied to generate a single cavitation bubble near the interface. To nucleate a single bubble, a laser pulse with a 532-nm wavelength is expanded and collimated by a beam expander, and then focused into a glass tank. A time delay trigger connected to the pulsed laser and two high-speed cameras is used to realize the synchronized recording of the two cameras after firing the laser pulse. Cavitation bubble dynamics near the oil film-water interface and the evolution of the lower interface (liquid‐liquid interface) are captured using the high-speed camera with a frame rate of 105 frame/s, whereas the evolution of the upper interface (gas-liquid interface) on a much longer time scale is recorded using a high-speed camera with a frame rate of 2000 frame/s.
The effects of the dimensionless distance γ and oil film thickness D on the cavitation bubble collapse characteristics and interface evolutions are explored. Owing to the existence of the oil film-water interface, the cavitation bubble collapses nonspherically, moves away continuously, and produces a high-speed jet away from the interface under different experimental conditions. The displacement of the cavitation bubble centroid increases logarithmically with an increase in the anisotropic parameter ζ (i.e., the decrease in γ), resulting from the enhancement of the interaction between the cavitation bubble and liquid‐liquid interface. As the total collapse shock wave energy decreases with increasing ζ, more energy is needed to drive the bubble rebound to a larger volume in the secondary period of bubble oscillation; therefore, the relative rebound radius also increases logarithmically with the increase in ζ. The lower interface of the oil film evolves during the bubble collapse, which is mainly caused by the inertia of the bubble oscillation. The upper interface evolves on a much longer time scale owing to the competing effects of interfacial tension, gravity, and viscosity. Three typical modes of liquid jet are observed for the upper interface: hump jet (Fig. 6), thin jet (Fig. 7), and two-tier jet (Fig. 8). Three typical modes of motion are also observed for the lower interface: slight disturbance (Fig. 9), inverted hill deformation (Fig. 10), and cone deformation (Fig. 11).
In this study, a single cavitation bubble is generated near the liquid‐liquid interface of the oil film and water using the pulsed laser-induced method. Two high-speed cameras are used to simultaneously record the cavitation bubble collapse and evolutions of the upper and lower interfaces of the oil film. The results show that the cavitation bubble generated near the oil‐water interface continuously moves away from the interface during the process of nonspherical collapse and develops a high-speed jet away from the interface. The relation between the displacement of the cavitation bubble centroid and anisotropic parameter ζ and the relation between the relative rebound radius and ζ are both logarithmic. The lower interface motion of the oil film is observed during the bubble collapse, whereas the upper interface starts to deform after the bubble collapse is over. Three typical liquid jet modes (hump jet, thin jet, and two-tier jet) are observed for the upper interface, and three typical motion modes (slight disturbance, inverted hill deformation, and cone deformation) are observed for the lower interface. In the case of a hump jet, the dimensionless maximum height hm follows the power law, hm ∝ γθ. The observations herein offer a deeper understanding of the cavitation dynamics and provide theoretical guidance for cavitation techniques.
