Production and dispersion of free radicals from transient cavitation Bubbles: An integrated numerical scheme and applications

Penetration of hydroxyl radicals in the aqueous phase surrounding a cavitation bubble

“…The choice of oxygen bubble is based on several previous sonochemical studies [19] , [20] , [21] , [22] that showed an improved removal efficiency of organic pollutants in wastewater treatment when oxygen is used as the sparging gas. Also, there are several theoretical investigations to analyze the radicals produced inside the oxygen bubble [3] , [15] , [23] . Our research follows these efforts and extends the focus to the penetration of radicals in the liquid phase.…”

“…Moreover, two salient features of the oxygen bubble make it an ideal prototype for studying sonochemical effects. First, compared with inert gases such as argon, the presence of oxygen can trigger more complex chemical reactions both inside and outside of the bubble [3] , [20] . On the other hand, however, OH radicals constitute the main bulk of radical yields [3] , [15] , just as in the case of an inert gas bubble.…”

“…First, compared with inert gases such as argon, the presence of oxygen can trigger more complex chemical reactions both inside and outside of the bubble [3] , [20] . On the other hand, however, OH radicals constitute the main bulk of radical yields [3] , [15] , just as in the case of an inert gas bubble. Considering that the recombination reactions are the main pathway for consuming radicals in the liquid phase, the reported penetration behavior based on oxygen bubbles can be translated to other inert gas bubbles.…”

“…The quasi-adiabatic collapse of microbubbles creates extreme conditions in the interior, where water vapor and other gases are dissociated into free radicals. Among the various products, the hydroxyl radical (OH • ) constitutes the bulk of the generated reactive species and plays a central role in the sonochemical reactions [2] , [3] , [4] , [5] . Owing to the high oxidation potential and nonselective nature, hydroxyl radicals can attack and degrade most organic pollutants, including those recalcitrant ones, such as hydrocarbons [6] , pesticides [7] , and pharmaceutical compounds [8] .…”

“…1 . Previous studies [3] , [12] have established that due to the slow diffusivity (on the order of 10 -5 cm 2 /s), the free radicals that escape from the bubble accumulate to high concentrations within a boundary layer near the gas–liquid interface. There, strong recombination reactions among the reactive species ensue and rapidly deplete the radicals.…”