Interaction between number of formed bubbles, reaction rate and flow velocity of acoustic streaming in the initiation period of power-induced quenching.

To elucidate the detailed process of power-induced quenching in which the rate of sonochemical reactions decreases sharply as ultrasonic power increases, the interaction between the number of formed bubbles, the sonochemical reaction rate, and the flow velocity of acoustic streaming was investigated during the initiation period of ultrasonic irradiation. The investigation is conducted through the observation of formed bubbles, particle image velocimetry (PIV) measurement, and sono-chemical luminescence (SCL) observation. The experimental findings suggest that the SCL intensity decreased after irradiation for a certain period at the ultrasonic power at which the power-induced quenching occurred. During the quenching process, the number of formed bubbles initially decreased due to the waveform distortion caused by sound waves emitted during the oscillations of the bubbles. Subsequent to the decline in the number of bubbles, the SCL intensity and the flow velocity of acoustic streaming decreased. As the ultrasonic power increases, the decrease in time of SCL intensity, number of formed bubbles, and the flow velocity of acoustic streaming becomes shorter. These phenomena can be interpreted by rectified diffusion, the mass flux of which is largely varied due to the ultrasonic wave distortion.