超音波音場における微小気泡の成長 : 2周波数重畳法によるRectified Diffusionの増強効果(流体工学,流体機械)  [in Japanese] Growth of an Oscillating Microbubble in an Ultrasound Field : Enhancement of Rectified Diffusion with a Dual-Frequency Excitation Method(Fluids Engineering)  [in Japanese]

Acoustic cavitation has an important role in ultrasound applications, such as HIFU (High Intensity Focused Ultrasound) therapy. Control of the growth of the cavitation bubbles is one of the important factors to control the effects of the cavitating bubbles. Several researchers have shown that a dual-frequency excitation method can enhance the growth of the bubbles due to rectified diffusion and consequently enhances the effects of the cavitation. In this study, the growth of an oscillating bubble in an ultrasound field due to the rectified diffusion is numerically investigated. In the model, we consider the compressibility of the surrounding liquid, mist generation inside the bubble, and the heat and mass transfer through the bubble interface. Mass transfer is calculated by solving the gas diffusion equation in liquid phase with the boundary condition at the bubble interface. The results reveal that the dual-frequency excitation method can enhance the rectified diffusion in certain cases and it can be useful to control the growth of the cavitating bubbles.