The range of ambient radius for an active bubble in sonoluminescence and sonochemical reactions

Abstract

Numerical simulations of nonequilibrium chemical reactions inside an air bubble in liquid water irradiated by ultrasound have been performed for various ambient bubble radii. The intensity of sonoluminescence (SL) has also been calculated taking into account electron-atom bremsstrahlung, radiative attachment of electrons to neutral molecules, radiative recombination of electrons and ions, chemiluminescence of OH, molecular emission from nitrogen, etc. The lower bound of ambient radius for an active bubble in SL and sonochemical reactions nearly coincides with the Blake threshold for transient cavitation. The upper bound is in the same order of magnitude as that of the linear resonance radius. In actual experiments, however, the distribution of ambient radius for active bubbles may be narrow at around the threshold ambient radius for the shape instability. The threshold peak temperature inside an air bubble for nitrogen burning is higher than that for oxidant formation. The threshold peak temperatures depend on ultrasonic frequency and acoustic amplitude because chemical reactions inside a bubble are in nonequilibrium. The dominant emission mechanism in SL is electron-atom bremsstrahlung except at a lower bubble temperature than 2000 K, for which molecular emissions may be dominant.

Sonochemical Treatment of Water Polluted by Chlorinated Organocompounds. A Review

“…This is of course dependent on the size of the bubbles involved. This issue is far from being closed, but modern experimental observations [80] and theoretical results [81,82] suggest that the chemically active bubbles are in fact much smaller than the resonant radius, at least at low frequency. Concerning the dissemination of OH · radicals, this strongly depends on whether or not the bubble breaks up in the final stages of the collapse.…”

Influence of microparticle size on cavitation noise during ultrasonic vibration

“…In the ultrasonic sound field, all the bubbles are force to oscillate under the ultrasonic waves, 17 and undergo hundreds of oscillations 18,19 until they collapse. For bubbles oscillating under the acoustic waves, the radiated pressure wave p r could be expressed 20 by…”

Size Distribution of Cavitation Bubbles

“…This approach works by stabilizing the bubble size distribution within the active radius range, since active bubbles oscillate strongly as a response to the applied acoustic pressure. According to Yasui et al (2008), the active radius range spans from the Blake threshold to radii on the order of linear resonance radii. However, Hauptmann et al (2013) reported the strongest cavitation activity when the bubble size distribution was centered on the linear resonance size.…”

“…Therefore, knowledge about the size distribution of cavitation bubbles is critical for promoting or suppressing the aforementioned physical effects in order to optimize or minimize, respectively, the corresponding cavitation activity. Earlier studies have demonstrated that the equilibrium radius of a cavitation bubble encompasses a range of radii rather than a single linear resonance radius calculated using the linear equation for a given frequency (Yasui et al 2008;Yasui 2002). Furthermore, because of nonlinearity, the actual equilibrium radii of cavitation bubbles are always smaller than the calculated single value (Yasui 2002;Luther et al 2001;Lee et al 2005).…”