Investigation of noninertial cavitation produced by an ultrasonic horn

Abstract

This paper reports on noninertial cavitation that occurs beyond the zone close to the horn tip to which the inertial cavitation is confined. The noninertial cavitation is characterized by collating the data from a range of measurements of bubbles trapped on a solid surface in this noninertial zone. Specifically, the electrochemical measurement of mass transfer to an electrode is compared with high-speed video of the bubble oscillation. This gas bubble is shown to be a "noninertial" event by electrochemical surface erosion measurements and "ring-down" experiments showing the activity and motion of the bubble as the sound excitation was terminated. These measurements enable characterization of the complex environment produced below an operating ultrasonic horn outside of the region where inertial collapse can be detected. The extent to which solid boundaries in the liquid cause the frequencies and shapes of oscillatory modes on the bubble wall to differ from their free field values is discussed.

A parametric review of sonochemistry: Control and augmentation of sonochemical activity in aqueous solutions

“…That is, an area beyond a point where no transient cavitation can be detected and only non-cavitation behaviour such as bubble motion, acoustic streaming, etc. occurs [189,190]. Vessels with a diameter greater than 90 mm have been shown to exhibit a reduction in sonochemical activity for a 60 mm diameter transducer [97].…”

“…The size and shape of the vessel for plate transducers can determine the influence of applied parameters and the cavitation activity [97,153,[188][189][190]. For larger vessels there is an increase of calorimetric power in the liquid with vessel diameter, however this does not necessarily translate to an increase in sonochemical activity [97].…”

Cavitation clusters in lipid systems – surface effects, local heating and streamer formation

“…For example, the piston like emitter (PLE) is a common sound source employed in HIU applications. The PLE system has been shown to produce a complex environment where hot spots 11,12 , bubbles, bubble clusters [13][14][15] , inertial 16,17 cavitation and non-inertial [18][19][20] cavitation exist and where different processes may be driven (for example surface erosion 21,22 , chemical changes [23][24][25][26][27] and mass transfer [28][29][30] effects). While many experimental studies of these effects in water environments exist, oils, and in particular lipids 31 have received little fundamental investigation.…”

Fast bubble dynamics and sizing

“…The advantage of using a single tethered bubble is that it prevents the occurrence of Doppler effects. The dynamics of the tethered bubble differ from those of the free bubble mainly by the dependence of the inertial (or added) mass on the contact angle [49][50][51]: the resonant frequency may be lowered down to 20percent. However, it was checked that in the case of a bubble with a radius ranging between 40 and 160 μm, no adhesion effects are visible in the volumetric vibrations as long as the bubble is not masked by the wire [35].…”