23 - Numerical insight into the liquid compressibility effect on the sonochemical activity of acoustic bubbles

Abstract

Listen

Translate article

Acoustic cavitation is the central event of the sonochemical process, which is one of the most recent advanced oxidation processes for water treatment. Even though the liquid compressibility effect on acoustic cavitation has already been investigated by certain studies, their results are still limited to the radial dynamics and the thermodynamic behavior of the gas inside the bubble. In this chapter, the liquid compressibility effect on the bubble dynamics and reactions occurring therein has been studied theoretically. A reaction scheme based on 25 reversible chemical reactions has been adopted for simulating the chemistry inside the bubble at the strong collapse. Numerical simulations have been conducted at various liquid temperatures (T∞=15°C–55°C) and diverse external static pressures (p∞=0.6–2atm), for different frequencies of ultrasound (355, 515, and 647kHz). It was found that including the liquid compressibility reduced the maximum bubble temperature (Tmax) and pressure (pmax) inside the bubble as well as the production rate of free radicals, particularly •OH (r•OH). While losses in Tmax and pmax decreased significantly with increasing liquid temperature and external static pressure, those obtained for (r•OH) showed the inverse trend; they increased significantly with increasing T∞ and p∞. Moreover, these obtained trends were frequency-dependent. Higher losses in Tmax and pmax, recorded at lower T∞ and p∞, become more pronounced at lower frequency (355kHz), whereas the higher r•OH obtained at higher T∞ and p∞ become more elevated at the lowest frequency (647kHz). As conclusion, the role of liquid compressibility could not be stopped at regarding its impact on Tmax and pmax achieved inside the bubble, as generally reported in the literature, but it should be extended to the chemical bubble yield, because the liquid compressibility showed controversial effect toward the bubble dynamics and the chemical activity of the bubble.