Relation between thresholds of free radical generation and atomization under ultrasound exposure

Abstract

The relationship between thresholds of free radical generation and atomization under ultrasound exposure was investigated to elucidate the mechanisms of ultrasonic atomization. In the experiments to gradually increase the transducer driving voltage, the free radical generation, a quick transition of the water surface shape from a protuberance to a fountain, and atomization had the same threshold. The experiments using the acoustic loading conditions with the different water surface shapes also confirmed this fact. Furthermore, a focused shadowgram of the ultrasound field taken using a small container that mimics the protuberance visualized the generation of spotty-shaped high-intensity nodes inside and near the boundary of the protuberance. These results indicate that the induction of cavitation promoted by the high-intensity nodes triggers the appearance of the fountain that leads to the creation of atomization.

Ultrasonic Atomization—From Onset of Protruding Free Surface to Emanating Beads Fountain—Leading to Mist Spreading

“…Bulk-liquid cavitation: As stated in Section 1 repeatedly, obtaining the information regarding the concurrent formation of cavitation-along with the structural transitioning of the free surface from flat to protruding to jetting-should be quite helpful (Simon et al, 2015;Aikawa and Kudo, 2021). While it is extremely difficult in the present study to capture any images of cavitation bubbles inside the protuberance, doing so through the bulk liquid above the UsA transducer up to the free surface has been attempted.…”

“…Aikawa and Kudo (2021) rendered useful insights, in terms of the thresholds in triggering free radical generation and atomization, into a demarcation in structural variation of the free surface. The former phenomenon is an outcome of the cavitation collapsing process; the latter should require the shape transition of free surface (Wang and Tsuchiya, 2022) from a protrusion to a "slender" fountain (of aspect ratio exceeding unity; Aikawa and Kudo, 2021). Upon increasing the transducer input power density, they detected essentially the identical threshold level, 2.5 W/cm 2 -for all these four [cavitation collapsing-free radical(s) generation-free-surface shape transition: from protuberance to prolate fountain-atomization] phenomena.…”

Ultrasonic measurement of thickness of carotid arterial wall using its natural longitudinal displacement

“…13) Many research have been conducted on high-intensity focused ultrasound therapy 14) and its safety. 15) Many ultrasonic studies involving measuring the properties of the intima-media complex (IMC) have been conducted to evaluate the degree and state of progression of atherosclerosis. [16][17][18][19][20][21] At present, the IMC thickness (IMT) of the carotid arterial wall measured using B-mode imaging is regarded as an indicator for diagnosis with a high level of evidence, [22][23][24] demonstrating its importance in the diagnosis of atherosclerosis.…”

High-speed photography of gas release from bioactive glass

“…[16][17][18][19][20] Liquid jet occurence has been associated with the generation of shock waves, 21) as well as the production of free radicals and heat. [22][23][24] To numerically simulate pulsations of released gas, solutions of the Rayleigh-Plesset equation were computed using the ode45 differential equation solver of MATLAB ® (The MathWorks, Inc., Natick, MA, USA) for initial bubble radii between 0.1 μm and 5.0 μm. 25) Bubble radii were plotted as a function of time, a so-called R(t) curve.…”