Phase difference sensitivity and stable output: Mechanisms of dual-frequency ultrasonic parameters in regulating cavitation intensity and sonochemical characteristics

This study systematically investigates the influence of acoustic amplitude, frequency combination, and phase difference on the dynamics of cavitation bubbles and their chemical products under dual-frequency ultrasound excitation. Through numerical simulations, the effects of phase difference (0–2π rad) variations on the maximum bubble radius (characterizing cavitation intensity), maximum oxidant yields, and the proportion of •OH radicals in the oxidants are analyzed under different amplitudes (Pe = 1.5, 2, 2.5, and 3 atm) and frequency combinations (20 + 40, 20 + 140, 20 + 200, 40 + 140, 40 + 200, and 140 + 200 kHz). The results show that the mechanism by which the phase difference affects cavitation varies significantly among different frequency combinations. High-frequency combinations (140 + 200 kHz) produce a stable cavitation enhancement effect that is independent of the phase difference, whereas the cavitation intensity and chemical output of low-frequency combinations (20 + 40 kHz) strongly depend on specific phase difference intervals. Increasing the acoustic amplitude significantly weakens the influence of the phase difference on all observed parameters, while simultaneously amplifying the effect of single-frequency excitation. Furthermore, it is found that •OH radicals consistently constitute the main component of the oxidants (proportion >50%), and their proportion can be regulated by adjusting the excitation parameters. This work provides an important theoretical basis and parameter design strategy for optimizing dual-frequency acoustic cavitation processes, enabling precise control for specific objectives, such as high-intensity acoustic cavitation, high-yield oxidant production, or selective generation of •OH radicals.