Ultrasonic waveform upshot on mass variation within single cavitation bubble: Investigation of physical and chemical transformations

Abstract

The mechanical disturbance created by an ultrasonic wave travelling through a liquid medium induces the formation of cavitation that oscillates due to rarefaction and compression of the wave. The duration and the magnitude of the pressure applied by the ultrasonic wave at each instant would generate a specific impact on the variation of the bubble radius, the temperature, the pressure and the mass inside it. In this paper, a numerical study is conducted to simulate four waveforms (sinusoidal, square, triangular and sawtooth) travelling an aqueous media saturated with oxygen with an amplitude of 1.5 and 2 atm and a frequency of 200, 300 and 500 kHz. The purpose is to highlight the mass evolution within acoustic cavitation bubble during one cycle due to physical transformations and sonochemical effect. The obtained results demonstrated that square signal enhances temperature and pressure growth inside the bubble, as well as mass transfer by evaporation and condensation. This leads to an improvement of produced quantities of free radicals but also to a selectivity of O as a major product in the detriment of HO and OH. These trends are less and less observed when passing to sinusoidal, triangular and square signal.

Numerical Characterization of Acoustic Cavitation Bubbles with Respect to the Bubble Size Distribution at Equilibrium

“…Let us consider a log-normal distribution [27,56,57] of the number density of bubbles according to their ambient radii, with an expected value of 3 µm, fairly acceptable as the average equilibrium radius at 300 kHz frequency [29]. The following notation is then adopted.…”

“…The probability of occurrence of each ambient radius in terms of number densities of bubbles is known by the resolution of the iterative algorithm. The number density related to each homogeneous sub-population is retrieved by the application of microscopic and macroscopic energy balances based on Equation (9) [57] and (10) [16,17,44], respectively. Equation (9) represents the energy balance applied on a single acoustic cavitation bubble of a radius R evolving in water under an oxygen atmosphere, within which 45 elementary chemical equations [13] are supposed to emerge, giving rise to 9 chemical species, as shown in Table 1.…”

Predicting the Sonochemical Efficiency for Water Decontamination: An Upscaled Numerical Approach

“…As the pressure drops to values below the saturating pressure of water, the cohesion of liquid molecules becomes no longer possible and the saturating gas, namely oxygen, is no longer soluble in the liquid, thus germs of gas tend to expand, inducing cavitation. As the wave evolves in function of time, the bubble radius R(x,t) 1) varies nonlinearly from R 0 according to the modified Keller-Miksis equation [8] accounting for the Hertz-Knudsen mass flow of water molecules at the interface [25].…”

The effect of organic ions on the formation and collapse of nanometric bubbles in ionic liquid/water solutions: A molecular dynamics study

“…In this context, the more complicated models give the same answer as the original Rayleigh-Plesset equation, then, we will only consider the RPE model in our discussion. [50][51][52][53][54][55] We extend these types of investigations to include solutions of organic salts belonging to the room temperature ionic liquids variety. Two compounds are considered, i.e., tetra-ethyl In what follows, tension θ is used as synonymous of negative pressure, and it is defined in the present context as θ = −P , with both P and θ being expressed in the same units, either bar or kbar.…”