Insight into the role of dissolution mechanism in the sonochemistry of acoustic cavitation bubble
Aissa Dehane, Slimane Merouani
Abstract
Abstract Using 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 ● , H 2 , and O 2 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: H 2 (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) > O 2 (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)>H 2 (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: H 2 > H ● > O > O 2 > ● OH > O 3 > HO 2 ● > H 2 O 2 . Nevertheless, above 213 kHz, this ranking starts to be disturbed with the dominance of the main species, i.e. H 2 , H ● , O, ● OH, and O 2 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.