Ultrasonic Cavitation Bubbles Research Articles

Numerical Simulation Study of Factors Influencing Ultrasonic Cavitation Bubble Evolution on Rock Surfaces during Ultrasonic-Assisted Rock Breaking

Numerical Simulation Study of Factors Influencing Ultrasonic Cavitation Bubble Evolution on Rock Surfaces during Ultrasonic-Assisted Rock Breaking

Removal of surface-attached micro- and nanobubbles by ultrasonic cavitation in microfluidics

Surface-attached micro- and nanobubbles are known for their resistance to external forces. This study experimentally and theoretically investigates their response to strong ultrasonic fields. Surface-attached micro- and nanobubbles with contact radii from 2 μm to 20 μm are generated in a microchannel and exposed to ultrasound through a vibrating glass substrate. At a driving frequency over 200 kHz up to 2 MHz tested, no significant response from the micro- and nanobubbles is observed. By contrast, at 100 kHz–200 kHz, ultrasonic cavitation bubbles appear in the microchannel and migrate toward the surface micro- and nanobubbles. Then the surface micro- and nanobubbles merge with the ultrasonic cavitation bubbles, detach from the substrate, and become free gaseous nuclei susceptible to further cavitation. Notably, the removal process leaves no observable residue. Theoretical analysis suggests that the directional migration of cavitation bubbles is driven by mutual acoustic radiation forces. This work demonstrates that ultrasonic fields can effectively remove surface micro- and nanobubbles, transforming them into free gaseous cavitation nuclei.

Shake, shear, and grind! - the evolution of mechanoredox polymerization methodology.

In the last half decade, mechanoredox catalysis has enabled an entirely new genre of polymerization methodology. In this paradigm, mechanical force, such as ultrasonic cavitation bubble collapse or ball mill grinding, polarizes piezoelectric nanoparticles; the resultant piezopotential drives the redox processes necessary for free- and controlled-radical polymerizations. Since being introduced, evolution of these methods facilitates exploration of mechanistic underpinnings behind key electron-transfer events. Mechanical force has not only been identified as a "greener" alternative to more traditional reaction stimuli (e.g., heat, light) for the synthesis of commodity polymers, but also a potential technology to enable the production of novel thermoplastic and thermoset materials that are either challenging, or even impossible, to access using conventional solution-state approaches. In this Feature Article, significant contributions to such methods are highlighted within. Advances and ongoing challenges in both ultrasound and ball milling driven reactions for radical polymerization and crosslinking are identified and discussed.

Desynchronization of neuronal firing in multiparameter ultrasound stimulation

Low-intensity transcranial ultrasound stimulation, a novel neuromodulation technique, that possesses the advantages of non-invasiveness, high penetration depth, and high spatial resolution, has achieved positive neuromodulation effects in animal studies. But the regulatory mechanism remains controversial. The intramembrane cavitation effect is considered one of the mechanisms for ultrasound neuromodulation. In this study, the modified equations of ultrasonic cavitation bubble dynamics were coupled with the dual-coupled neuron Hindmarsh-Rose model, small-world neural network model, and the Jansen-Rit neural mass model, which simulate simple coupled neurons, complex neuronal networks, and discharge signals in epileptic disorders respectively. The results demonstrated that ultrasound stimulation has an appreciable modulatory effect on neuronal firing desynchronization in Hindmarsh-Rose model and small-world neural network model. The desynchronization effect is related to the stimulation frequency and intensity. Furthermore, ultrasound stimulation has an inhibitory effect on epileptic seizures, and the effect is enhanced by increasing ultrasound frequency from 0.1–1.0 MHz. This is the first combination of ultrasonic intramembrane cavitation effect theory with neurons and neural network firing desynchronization, which can provide guidance of parametric and theories support for the studies of neurological diseases such as epilepsy and Parkinson’s disease.

Molecular dynamics simulation of ultrasound cavitation occurring in copper–water nanofluid

It is necessary to reveal the impact of nanoparticles on ultrasonic cavitation phenomena in nanofluids, which is conducive to the heterogeneous nucleation applications of ultrasonic cavitation. In this work, the ultrasonic cavitation processes in pure water and nanofluids were simulated by molecular dynamics. Then, the effect of nanoparticles on ultrasonic cavitation was investigated by adding alternate positive and negative pressure waves. After that, the formation of critical bubbles in cavitation and the collapse of nanobubbles by shock waves were studied by using Voronoi mosaic method and rigid body model, respectively. Finally, the regenerated nanobubbles were analyzed after the collapse of nanobubbles. The results show that the nanoparticles could promote the formation of nanobubbles, and consequently, the nano-jets and nanoparticles movement occur during the collapse of nano-bubbles. Additionally, more tiny cavities generated after the collapsing of nanobubbles and the number of nanobubbles during second cycle will be larger than that of the first cycle. As a result, some of these cavities promote the generation of multiple ultrasonic cavitation bubbles in the subsequent ultrasonic cycle. This leads to the chain reaction effect of ultrasonic cavitation phenomenon occurring in nanofluids.

Simulation of dynamic process of double bubble coupled acoustic cavitation

In order to simulate the acoustic cavitation process of double-bubble coupling, based on the fluid dynamics governing equation and fluid volume fraction model, this paper proposes a three-dimensional finite element simulation model of double-bubble coupled ultrasonic cavitation in Fluent software, and numerically simulates the dynamic process of double-bubble coupled acoustic cavitation in fluid driven by ultrasonic wave. The nonlinear dynamic characteristics of coupled acoustic cavitation with double bubbles are studied by evaluating the variation of the acoustic field around the cavitation bubble. The results indicate that under the ultrasonic drive, the spherical bubbles gradually widen first to the maximal radius, then shrink swiftly, and finally collapse. There is an interaction force between the paired double bubbles, which inhibits the expansion of cavitation bubbles and increases the bubble contraction time. The ability of the cavitation bubble to converse the energy is strengthened in the contraction stage. Compared with the acoustic cavitation of the single bubble, the pressure inside the bubble is expanded when the coupled double bubble collapses. The analysis results in this paper will provide the reference for the dynamic process simulation of the ultrasonic cavitation bubbles.

Preparation of boron nitride nanosheets by glucose-assisted ultrasonic cavitation exfoliation.

Boron nitride nanosheets (BNNSs) have been widely used in many fields due to their excellent properties. However, low preparation rates and difficulty in functionalization hinder their further development. This study proposes a novel glucose-assisted ultrasonic cavitation exfoliation (GAUCE) method with glucose as an auxiliary solution to prepare BNNSs. Results show that the method has a high preparation yield of 55.58%, which is higher than the average preparation yield of 33.86%. The mechanism of preparing BNNSs by GAUCE was also investigated. The exfoliation of BNNSs was achieved using the energy of ultrasonic cavitation bubble collapse, which will break the interlayer forces in h-BN. The grafting of hydroxyl groups decomposed by glucose on the edge and surface of BNNSs during cavitation prevented the re-aggregation of the nanosheets, thereby increasing the exfoliation yield of BNNSs. In addition, the contact angle of BNNSs prepared by GAUCE was reduced, and the hydrophilicity was greatly improved.

Ultrasonic cavitation bubble- and gas bubble-assisted fractional precipitation for the purification of (+)-dihydromyricetin

Ultrasonic cavitation bubble- and gas bubble-assisted fractional precipitation for the purification of (+)-dihydromyricetin

Experimental investigation on the ultrasonic impregnation of wood through measurements of the intensity of sonoluminescence

Ultrasonic impregnation is thought to be an effective way of permeation of liquid into material through the material-surface reforming with the attack by an ultrasonic cavitation jet or by the shock wave emitted from a collapsing bubble, or through dynamic transformation of material like a sponge. The action of a cavitation bubble can also provide penetration of liquid into the interior of the material. This paper investigates whether there is a correlation between the intensity of sonoluminescence (SL) measured at different positions and the increment in the mass of the wood material (cedar) after sonication with immersion into water in order to clarify the role of cavitation bubbles for ultrasonic impregnation. It was found that a high mass change was obtained for the material located at the position for high (the maximum) SL intensity. The number density of ultrasonic cavitation bubbles that are able to collapse leading to the emission of SL is correlated with the degree of ultrasonic impregnation.

When Bubbles Are Not Spherical: Artificial Intelligence Analysis of Ultrasonic Cavitation Bubbles in Solutions of Varying Concentrations.

Ultrasonic irradiation of liquids, such as water-alcohol solutions, results in cavitation or the formation of small bubbles. Cavitation bubbles are generated in real solutions without the use of optical traps making our system as close to real conditions as possible. Under the action of the ultrasound, bubbles can grow, oscillate, and eventually collapse or decompose. We apply the mathematical method of separation of motions to interpret the acoustic effect on the bubbles. While in most situations, the spherical shape of a bubble is the most energetically profitable as it minimizes the surface energy, when the acoustic frequency is in resonance with the natural frequency of the bubble, shapes with the dihedral symmetry emerge. Some of these resonance shapes turn unstable, so the bubble decomposes. It turns out that bubbles in the solutions of different concentrations (with different surface energies and densities) attain different evolution paths. While it is difficult to obtain a deterministic description of how the solution concentration affects bubble dynamics, it is possible to separate images with different concentrations by applying the artificial neural network (ANN) algorithm. An ANN was trained to detect the concentration of alcohol in a water solution based on the bubble images. This indicates that artificial intelligence (AI) methods can complement deterministic analysis in nonequilibrium, near-unstable situations.

Ultrasonic cavitation bubble- and gas bubble-assisted adsorption of paclitaxel from Taxus chinensis onto Sylopute

Ultrasonic cavitation bubble- and gas bubble-assisted adsorption of paclitaxel from Taxus chinensis onto Sylopute

Inactivation of Algae and Plankton by Ultrasonic Cavitation

Microbial treatment by ultrasonic waves has been attracting attention as a useful water treatment technology because it does not use special chemicals and the equipment is simple. In addition, because microbial cells are destroyed during treatment, it can be applied to ingredient extraction technology. Although ultrasonic cavitation bubbles are thought to be involved in the processing mechanism, the details of the mechanism remain unclear. The purpose of this study was to elucidate the destruction mechanism of algae, microcapsules, and plankton by ultrasonic waves. Each sample was irradiated with ultrasonic waves over a wide range of frequencies, and frequency dependence was observed in all the samples. For algae and microcapsules, we matched the frequencies against the resonance frequency calculated based on the mechanical resonance model using adjacent ultrasonic cavitation bubbles. As a result, a good match was found. For plankton, partial damage to the shape was observed after ultrasonic irradiation, suggesting that shear stress, which is a local action caused by bubbles, was involved. By estimating the shear stress value based on the vibration equation of bubble, it was confirmed that the tendencies match.

Dynamic characteristics of bubbles in spherical bubble group considering evaporation and condensation of water vapor

<sec>In order to explore the dynamic characteristics of bubbles in the cavitation bubble cluster in detail, the dynamic equation of a bubble with arbitrary location inside the bubble cluster is established in this paper, based on the interactions between bubbles inside the bubble cluster driven by ultrasound. The effects of evaporation and condensation of the water vapor are also taken into account in the derivation process. Based on the proposed equation, the influences of the bubble position, number of bubbles, and initial radius of bubbles on the dynamic characteristics of cavitation bubbles are studied, and the corresponding change laws of the bubble radius, energy, temperature, pressure, as well as the number of water vapor molecules in a bubble are investigated under ultrasound.</sec><sec> The calculation results are shown below. 1) Comparing with an isolated bubble, the oscillation of a bubble inside the bubble cluster is suppressed by its surrounding bubbles, which leads to the fact that the vibration amplitude of a bubble inside the bubble cluster is smaller, and that the internal energy, maximum temperature, maximum pressure and the number of water molecules in the bubble all become smaller. As the distance between the bubble and the center of the bubble cluster increases, the vibration amplitude of the bubble become larger. 2) The initial radii of the bubbles in the bubble cluster can significantly affect the normalized vibration amplitude, collapse time, internal energy, temperature, and pressure of bubbles, as well as the number of water vapor molecules in bubbles of the bubble cluster. 3) As the number of bubbles in the bubble cluster increases, the vibration amplitudes of the bubbles decrease. 4) The higher the ultrasonic frequency, the smaller the oscillation amplitude of the bubble; the smaller the maximum pressure and energy of the bubble, the larger the minimum value of the internal pressure and temperature of the bubble and the less the number of water molecules in the bubble. When the ultrasonic frequency increases, the cavitation effects of bubbles in the bubble cluster are suppressed. 5) As the ultrasonic sound pressure increases, the oscillation amplitudes of the bubbles in the bubble cluster increase, the maximum values of the bubbles' radii increase, the collapse times of the cavitation bubbles increase, and the number of oscillations of bubbles decreases after the cavitation bubbles have collapsed. Additionally, the maximum value of internal energy, temperature, pressure, and the number of water molecules in the bubble also increase as the ultrasonic sound pressure increases, while the minimum value of the pressure and temperature of the bubble decrease. Besides, when the ultrasonic sound pressure increases, the cavitation effects of the bubbles in the bubble cluster turn stronger.</sec><sec> This paper focuses on the dynamic characteristics of ultrasonic cavitation bubble cluster from the theoretical aspect and the results can be further applied to experimental analysis.</sec>

Increase the yield of bioactive compounds from elder bark and annatto seeds using ultrasound and microwave assisted extraction technologies

We describe techniques to rapidly increase the yield of bioactive compounds from plant sources such as elder bark and annatto seeds using microwave dielectric heating and ultrasonic cavitation bubbles, a substantial improvement over conventional heating methods. For elder bark, the optimal extraction parameters were obtained with ethanol, using 0.01Lg−1 of solvent to material and extracting for at least an hour at 55°C. Ursolic acid was found to be more abundant in barks. Under the optimal conditions, the yields of oleanolic acid and ursolic acid were about 86% while using ultrasound assisted extraction and about 92% while using microwaves, respectively. Using the optimal extraction parameters for annatto seeds: ethyl acetate, the ratio of solvent to material at 0.05Lg−1 and at least 30min. extraction time, the yield of bixin reached about 85% with sonication and 95% with microwave heating. Assisted extraction techniques, with microwave assisted extraction being the most optimal technique, enhanced the extraction efficiencies and extracted higher concentrations when compared to standard methods.

Sonochemical degradation of surfactants with different charge types: Effect of the critical micelle concentration in the interfacial region of the cavity

Ionic surfactants tend to accumulate in the interfacial region of ultrasonic cavitation bubbles (cavities) because of their surface active properties and because they are difficult to evaporate in cavitation bubbles owing to their extremely low volatilities. Hence, sonolysis of ionic surfactants is expected to occur in the interfacial region of the cavity. In this study, we performed sonochemical degradation of surfactants with different charge types: anionic, cationic, zwitterionic, and nonionic. We then estimated the degradation rates of the surfactants to clarify the surfactant behavior in the interfacial region of cavitation bubbles. For all of the surfactants investigated, the degradation rate increased with increasing initial bulk concentration and reached a maximum value. The initial bulk concentration to obtain the maximum degradation rate had a positive correlation with the critical micelle concentration (cmc). The initial bulk concentrations of the anionic surfactants were lower than their cmcs, while those of the cationic surfactants were higher than their cmcs. These results can be explained by the negatively charged cavity surface and the effect of the coexisting counterions of the surfactants.

Cavitation bubble- and gas bubble-induced fractional precipitation of paclitaxel from Taxus chinensis

In this study, a fractional precipitation technique of paclitaxel using ultrasonic cavitation bubbles and gas bubbles is presented. Precipitation efficiency has been dramatically improved, and the time required for precipitation has been reduced by 20–30 times compared to conventional methods. As a result of investigating the mechanism of fractional precipitation in which cavitation and gas bubbles were introduced, it was found that the bubble surface itself acts as a nucleation site, resulting in faster nucleation and thereby improving precipitation efficiency. In addition, compared to the conventional fractional precipitation, the particle size was reduced by 7.8–8.9 times and 4.7–4.9 times for cavitation bubbles and gas bubbles, respectively, and the diffusion coefficient was increased by 10.3–11.9 times (cavitation bubble) and 4.7–4.9 times (gas bubble).

Enhanced Disintegration of Silicon Particles due to their Mutual Impact Caused by Ultrasonic Cavitation Bubbles

Fast development of nanotechnology leads to the top-down preparation of nanoparticles by various disintegration techniques taking a major part in the industrial sector. A very promising way seems to be the use of cavitation implosions. In our approach, the main mechanism of this type of disintegration is based on mutual collisions of solid microparticles in dense dispersions, powered by implosions of vapour cavitation bubbles generated between the particles.This paper presents experimental results of the disintegration of silicon microparticles to the sub-micron scale. In our experiments, the primary silicon particles of mean size of 5927 nm were reduced to 160 nm and 736 nm by the ultrasonic disintegration process after 240 minutes and at the ultrasonic frequency of 32 kHz. We also present a phenomenological model of particles erosive disintegration where particle fragments are approximated by spheres of equivalent volume. This model allows us to calculate the energy needed for successful disintegration of primary microparticles by measuring the particle size distribution. Thus, we can estimate the minimal energy conserved in the cavitation bubble alongside with its radius at a normal pressure of the surrounding liquid.

Investigation of Impact Loads Caused by Ultrasonic Cavitation Bubbles in Small Gaps

Ultrasonic cavitation shows a great potential in various industrial applications such as sonochemistry, food processing, ultrasonic cleaning, and surface treatments. These applications have the advantages of high temperatures or high pressure due to the collapse of cavitation bubbles. In surface treatments, the collapse of bubbles occurs near workpiece surfaces and creates micro-jets which lead to high impact forces. As one of these surface treatment processes, ultrasonic cavitation peening requires a small gap between the vibration source and the treated surface to obtain the maximum impact force. Due to these small gaps, the growth and collapse of cavitation bubbles are affected, which result in the changes of impact forces. Therefore, the investigation of the impact loads caused by ultrasonic cavitation bubbles in small gaps is the focus of this contribution. A theoretical model taking into consideration bubble interactions is utilized to estimate the optimal standoff distance at which the largest impact forces occur. Then, experimental investigations are carried out. A piezoelectric sensor with a titanium alloy cover is used to record the number of impacts and their amplitudes. The recorded signals are then processed in time and frequency domains. The experimental results show that large impact loads are generated when the gap width is in the range of 0.5–0.8 mm. It is also found that the maximum working efficiency occurs in this range.

Process mechanism in ultrasonic cavitation assisted fluid jet polishing

Material removal rate in fluid jet polishing is significantly enhanced when ultrasonic cavitation bubbles are introduced at the nozzle outlet. In this paper, two theories are put forward to explain the process mechanism: a micro-scale hypothesis in which the surface is micro-jetted by collapsing bubbles, and a macro-scale hypothesis in which vibration of the fluid in the impingement region increases abrasive particle erosive action. Experimental investigation suggests the higher likelihood of the macro-scale phenomenon, and a material removal model is proposed accordingly. Process footprints simulated by this model were found to agree well with experimental measurements.

Visualization of ultrasonic cavitation bubbles near an oil-deposited glass surface

Visualization of ultrasonic cavitation bubbles near an oil-deposited glass surface