Based on the periodic oscillation of the stable acoustic cavitation bubble, we present a precise measure-ment technique for the bubble evolution. This technique comprises the lighting engineering of pulsing laser beam whose phase can be digitally shifted, and the long distance microphotographics. We used a laser, an acousto-optic modulator, a pulse generator, and a long distance microscope. The evolution of a levitated bubble can be directly shown by a series of bubble’s images at different phases. Numerical simulation in the framework of the Rayleigh-Plesset bubble dynamics well supported the experimental result, and the ambient radius of the bubble, an important parameter re-lated to the mass of the gas inside the bubble, was obtained at the same time.
The current work proposes a model describing the dynamics of coated microbubbles, which simplifies the traditional three-layer model to a two-layer one by introducing a visco-elastic interface with variable surface tension coefficients to connect the gas zone and the liquid zone. In the modified model, the traditional two interfaces boundary conditions are combined into one to simplify the description of the bubble. Moreover, the surface tension coefficient is defined as a function of bubble radius with lower and upper limits, which are related to the buckling and rupture mechanisms of the bubble. Further discussion is made regarding the effects resulting from the change of the surface tension coefficient on bubble dynamics. The dynamic responses of Optison and Sonozoid microbubbles, measured experimentally based on light scattering technology (adapted from previously published work), are simulated using both classic three-layer models (e.g. Church's model) and simplified model. The results show that our simplified model works as well as the Church's model.
The mass-exchange between the inside and outside of a cavitation bubble is a complicated process with several kinds of exchange forms acting together, such as gas diffusion, gas-liquid phase transition, chemical reactions and so on. A phenomenological model of mass-exchange was proposed, in which the pressure difference is considered as the drive. Compared with the previous physical models, it has a simpler form and less computational cost. Combining it with Rayleigh-Plesset equation, the equilibrium radius is calculated when the mass-exchange achieves the dynamic balance. The result shows that the equilibrium radius has multiple values. The relationships between the equilibrium radius and the driving ultrasound (pressure amplitude and frequency) are evaluated. We also investigated how these relationships were affected by the model parameters. Finally, the bubble radius evolution in the sulfuric acid driven by different pressures was measured. The experimental result that the equilibrium radius changes with the pressure agrees with the numerical results well.
Single-bubble sonoluminescence (SBSL) is achieved with strong stability in sulfuric acid solutions. Bubble dynamics and the SBSL spectroscopy in the sulfuric acid solutions with different concentra- tions are studied with phase-locked integral stroboscopic photography method and a spectrograph, respectively. The experimental results are compared with those in water. The SBSL in sulfuric acid is brighter than that in water. One of the most important reasons for that is the larger viscosity of sulfuric acid, which results in the larger ambient radius and thus the more contents of luminous material inside the bubble. However, sonoluminescence bubble’s collapse in sulfuric acid is less violent than that in water, and the corresponding blackbody radiation temperature of the SBSL in sulfuric acid is lower than that in water.
