Insight into the role of dissolution mechanism in the sonochemistry of acoustic cavitation bubble

Abstract

AbstractUsing a detailed numerical model, in the present work, the dissolution process of the different species generated by the acoustic cavitation bubble was investigated through the analysis of bubble chemistry over a range of wave frequencies from 140 to 515 kHz. It has been observed that during the first bubble collapse, at 140 and 213 kHz, significant amounts of ●OH, O, H●, H2, and O2 molecules (from ~ 2.1×10‐20 to 4.86×10‐18 mol) are dissolved into the bulk liquid (2.84‐0.067%). However, with the rise of ultrasound frequency (>213 kHz), the number and the quantity of the dissolved substances are decreased (<1.16×10‐20 mol) until to be completely suppressed at 515 kHz. Over the first compression period, at 140 and 213 kHz, the dissolution tendency is in the order: H2 (4.86×10‐18‐9.44×10‐19 mol) > H● (4.41×10‐18‐7.76×10‐19 mol) > O (1.8×10‐18‐2.75×10‐19 mol) > ●OH (4.68×10‐19‐1.91×10‐19 mol) > O2 (8.43×10‐20‐2.1×10‐20 mol). Nevertheless, at 355 kHz, the dissolution of the main substances is in the order: H● (1.16×10‐20 mol)>●OH (5.13×10‐21 mol)>H2 (3.59×10‐21 mol). Despite the low dissolution percentages of the different species (compared to the total yield) during the first bubble collapse (<3%), it has been observed that the corresponding molar amounts (depending on the applied frequency) are of great importance (≤ 4.86×10‐18 mol). On the other hand, independently of the number of acoustic cycles (1, 2 or 3), the dissolution tendency of the different species, at 140 and 213 kHz, is in the order: H2 > H● > O > O2 > ●OH > O3 > HO2● > H2O2. Nevertheless, above 213 kHz, this ranking starts to be disturbed with the dominance of the main species, i.e. H2, H●, O, ●OH, and O2 molecules. According to the obtained findings in the present paper, the importance of the dissolution mechanism (into the bubble chemistry) is clearly evidenced; therefore, for an accurate simulation of the chemistry of an acoustic cavitation bubble, the consideration of the dissolution process should be taken into account throughout the bubble's oscillation.