Ryuya Hayashi, Takuya Yamamoto
The power-induced quenching for sonochemical reactions in which the rate of sonochemical reactions decreases sharply as ultrasonic power increases is interpreted by a multiscale numerical simulation based on the Caflisch model. The utilization of a representative acoustic bubble for each numerical grid cell facilitated the numerical modeling of the interaction between the fundamental ultrasonic wave and the sound emission and absorption from the bubbles. The numerical results indicated that the waveform of ultrasound is largely distorted by the sound emission and absorption from the bubbles, generating harmonics and broadband noise. In the highly distorted conditions, the maximum temperature at the moment of bubble collapse experiences a substantial decrease, which contributes to the phenomenon of power-induced quenching. While the larger bubble number density and larger equilibrium bubble radius result in heightened sound emission and absorption from the bubbles, leading to a modest decline in the maximum temperature within the bubble, the predominant factor contributing to the temperature decrease and the sound emission and absorption is the sound pressure amplitude. This finding further substantiates the phenomenon of power-induced quenching. The sound wave maintains a standing wave configuration at a low-pressure amplitude, but transitions into a traveling wave configuration at a high-pressure amplitude due to the process of sound emission and absorption from the bubbles. In the traveling wave field, the temperature within the bubble is observed to decrease, while the distribution of the high-temperature zone becomes more extensive. This phenomenon aligns closely with the outcomes of previous experimental studies.