Dual frequency ultrasonic cavitation in various liquids: High-speed imaging and acoustic pressure measurements

Abstract

Ultrasonic cavitation is used in various processes and applications, utilising powerful shock waves and high-speed liquid jets generated by the collapsing bubbles. Typically, a single frequency source is used to produce the desired effects. However, optimisation of the efficiency of ultrasound reactors is necessary to improve cavitation activity in specific applications such as for the exfoliation of two dimensional (2D) materials. This research takes the next step to investigate the effect of a dual frequency transducer system on the bubble dynamics, cavitation zone, pressure fields, acoustic spectra and induced shock waves for four liquids with a range of physical properties. Using ultra-high-speed imaging and synchronised acoustic pressure measurements, the effect of ultrasonic dual frequencies on bubble dynamics was investigated. The addition of a high frequency transducer (1174 kHz) showed that the bubble fragments and satellite bubbles induced from a low frequency transducer (24 kHz) were able to extend their lifecycle, increase spatial distribution, thus, extending the boundaries of the cavitation zone. Furthermore, this combination of ultrasonic frequencies generated higher acoustic pressures (up to 180%) and enhanced the characteristic shock wave peak, indicating more bubble collapses and the generation of additional shock waves. The dual frequency system also enlarged the cavitation cloud size under the sonotrode. These observations specifically delineated the enhancement of cavitation activity using a dual frequency system pivotal for optimisation of existing cavitation-based processing technologies.

Green Metrics Evaluation on The Cannizzaro Reaction of p-Anisaldehyde and Benzaldehyde Under Solvent-Free Conditions

“…This showcases ultrasonication's efficiency over reflux, attributed to its cavitation effect induced by ultrasonic or acoustic waves causing bubble formation and bursting in liquids. The presence of ultrasonic waves will increase the number of active cavitation bubbles which will increase the efficiency of the reaction by increasing the reaction rate, speeding up the reaction, 18 and increasing the local temperature and pressure of the liquid 20,21 . Therefore, the Cannizzaro reaction using the ultrasonic method is faster than the reflux method.…”

“…Table 1. is the result of the energy calculation of the ultrasonication and reflux method which is obtained from the formula of the equation that has been reported by 30 on research by 21 . According to Table 1.…”

Synergistic Enzyme‐Mimetic Catalysis‐Based Non‐Thermal Sonocavitation and Sonodynamic Therapy for Efficient Hypoxia Relief and Cancer Ablation

“…[22,23] However, cavitation events need a high acoustic pressure and continuously stable cavitation nuclei, [24,25] which is also difficult to control because any pocket present in the tissue may act as a nucleation site for initiation of random cavitation events. [26,27] Previous work involving the microbubbles contrast agents, [28,29] phase-shift perfluorooctyl bromide nanovesicles, [30] and perfluorohexane-encapsulated fullerene [31] into ultrasonic histotripsy has been proven to be an efficient method to increase cavitation nuclei and reduce cavitation threshold. [32][33][34][35] However, this method is still unsatisfactory since they allow cavitation for a very short time under pHIFU due to the rupture of their stabilizing gas shells.…”

“…[ 22,23 ] However, cavitation events need a high acoustic pressure and continuously stable cavitation nuclei, [ 24,25 ] which is also difficult to control because any pocket present in the tissue may act as a nucleation site for initiation of random cavitation events. [ 26,27 ]…”

Behaviors of cavitation bubbles driven by high-intensity ultrasound

“…Due to the secondary acoustic radiation generated by cavitation bubbles in ultrasound fields, bubble-bubble interactions should be considered to explain cavitation effects, such as the promotion or suppression of bubble oscillations, [1] which also depend on the splitting, polymerization, and nonspherical deformation of bubbles. [3][4][5][6] When multiple bubbles coexist in cavitation field, the coupling effect of bubbles cannot be ignored. Haghi et al [7] studied the collective nonlinear behaviors of bubbles in polydisperse bubble clusters, and found that the large microbubbles in clusters can force the small microbubbles to generate periodic frequency doubling and subharmonic oscillation.…”