Effect of frequency ratio and phase difference on the dynamic behavior of a cavitation bubble induced by dual-frequency ultrasound

Abstract

The best cavitation can be obtained only with an appropriate frequency ratio and phase difference. To optimize dual-frequency ultrasonic cavitation and to analyze the influence of the frequency ratio and phase difference, a dynamic model of dual-frequency ultrasonic cavitation that considers energy and material exchange inside and outside the bubble was established. The results show that the negative-pressure amplitude of dual-frequency ultrasound is higher than that of single-frequency ultrasound for the same energy input. For a harmonic, the phase difference that results in a maximum of the negative-pressure amplitude of dual-frequency ultrasound is periodic for different frequency ratios. The phase difference that results in expansion–contraction oscillations of the bubble changes periodically as 1.5π → π → 0.5π → 0 → 1.5π for different frequency ratios. The maximum bubble radius and the maxima of the pressure, energy, and number of water vapor molecules inside the bubble all reduce spirally and the intensity of cavitation decreases with an increase of the frequency ratio. Compared with a harmonic, the maxima of the cavitation parameters are less affected by the phase difference for an ultraharmonic. Therefore, similar cavitation can be easier to obtain by employing an ultraharmonic, which is helpful in achieving stable cavitation.