Cavitation Bubbles Research Articles

Fingering of a cavitation bubble in a thin gap: Ejection of the reversed boundary layer into the bulk flow

Fingering of a cavitation bubble in a thin gap: Ejection of the reversed boundary layer into the bulk flow

Correlation of Escherichia coli inactivation with histotripsy bubble cloud size

Bacterial loads can be effectively reduced with cavitation-mediated focused ultrasound, or histotripsy. Our previous in vitro work with Escherichia coli (E. coli) established strong trends of bactericide with increasing peak negative pressure amplitude, pulse length, PRF, and treatment time. The current study correlates bactericide as a function of the histotripsy bubble cloud size produced for these treatment parameters at several frequencies. Histotripsy was applied to E. coli suspensions in 10-ml sample vials at 810 kHz, 1.2 MHz, or 3.25 MHz for 40 min. Separately, cavitation was recorded using a Photron Fastrax high-speed camera for acoustic parameters equivalent to those used in the E. coli studies. The images were used to quantify the maximum size of each bubble cloud, with the assumption that the cloud was axially symmetric around the propagation direction. A strong linear relationship exists between log kill versus cloud size (R2 = 0.96). Remarkably, across all variables studied, the log-reduction in viable bacteria exhibited a direct proportional relationship with the dimensions of the bubble cloud. This strong correlation between bacterial reduction and cavitation bubble cloud size could have significance for clinical applications where bacteria cannot easily be sampled. [Work supported by NIH R01AR080120 and R01EB023910.]

BIMBAMBUM: A potential flow solver for single cavitation bubble dynamics

In the absence of analytical solutions for the dynamics of non-spherical cavitation bubbles, we have implemented a numerical simulation solver based on the boundary integral method (BIM) that models the behavior of a single bubble near an interface between two fluids. The density ratio between the two media can be adjusted to represent different types of boundaries, such as a rigid boundary or a free surface. The solver allows not only the computation of the dynamics of the bubble and the fluid-fluid interface, but also, in a secondary processing phase, the computation of the surrounding flow field quantities. We present here the detailed implementation of this solver and validate its capabilities using theoretical solutions, experimental observations, and results from other simulation softwares. This solver is called BIMBAMBUM which stands for Boundary Integral Method for Bubble Analysis and Modeling in Bounded and Unbounded Media. Program summaryProgram Title: BIMBAMBUMCPC Library link to program files:https://doi.org/10.17632/89vv35pmhr.1Licensing provisions: GPLv3Programming language: C++ and PythonNature of problem: The code solves the axisymmetric dynamics of single cavitation bubble in the vicinity of different types of boundaries. The boundaries are treated as an interface between two fluids, where the fluids can have different density ratios. The two fluids are considered inviscid and incompressible and the associated flows irrotational so that Laplace's equation is valid everywhere.Solution method: A boundary integral method is used to calculate the velocities on the discretized bubble surface and the fluid-fluid interface. The position of these boundaries can then be updated in time using a Lagrangian approach. In the fluid domain surrounding the bubble, the velocities and pressure are estimated using a combination of the boundary integral method and finite differences.Additional comments including restrictions and unusual features: The code solves the bubble dynamics as long as its surface remains simply connected.

Synchrotron X-ray phase-contrast imaging of ultrasonic drop atomization

Ultrasonic atomization is employed to generate size-controllable droplets for a variety of applications. Here, we minimize the number of parameters dictating the process by studying the atomization of a single drop pending from an ultrasonic horn. Spatiotemporally resolved X-ray phase-contrast imaging measurements show that the number-median sizes of the ejected droplets can be predicted by the linear Navier–Stokes equations, signifying that the size distribution is controlled by the fluid properties and the driving frequency. Experiments with larger pendant water drops indicate that the fluid–structure interaction plays a pivotal role in determining the ejection onset of the pendant drop. The atomization of viscoelastic drops is dictated by extended ligament formation, entrainment of air, and ejection of drop-encapsulated bubbles. Existing scaling laws are used to explain the required higher input amplitudes for the complete atomization of viscoelastic drops as compared to inviscid drops. Finally, we elucidate the differences between capillary wave-based and cavitation-based atomization and show that inducing cavitation and strong bubble oscillations quickens the onset of daughter drop ejection but impedes their size control.

A semi‐empirical approach for determining the number density and void fraction of acoustic cavitation bubbles in sono‐reactors

AbstractA new semi‐empirical technic has been established relying on the linkage between the chemistry in the bulk liquid and that taking place in the acoustic cavitation bubble. The open‐source COPASI software has been used for the optimization of number density according to the total yield of a single bubble and the fitting of the experimental yield of hydrogen peroxide in the sonicated solution. It was observed that the number density is increased with the rise of ultrasound frequency from 200 to 1140 kHz, independently of the saturating gas nature (O2, Ar or air). Within this range of wave frequencies, i.e. from 200 to 1140 kHz, the number of active bubbles goes up from 9.35 × 107 to 3.65 × 1015 L−1 s−1. On the other side, it has been demonstrated that the number density obtained under air atmosphere is greater than that resulting either under argon or oxygen‐saturating gas. Interestingly, with respect to the saturating gas nature (O2, Ar, air) and the range of ultrasound frequency (200–1140 kHz), it was observed that the increase of number density was not necessarily accompanied by a proportional increase of void fraction (total volume of bubbles).

Biofilm removal from Difficult-to-Reach places via secondary cavitation within a constrained geometry mimicking a Periodontal/Peri-Implant pocket

Biofilm removal from the apical region of the periodontal or peri-implant pocket, which is very difficult to achieve with mechanical instruments, is a major unresolved issue in dentistry. Here, we propose the use of photoacoustically induced streaming and secondary cavitation to achieve superior cleaning efficacy in the apical region of the periodontal and peri-implant pocket. We have used a prefabricated narrow wedge system that mimics the consistency of periodontal and peri-implant pockets of both healthy and severely inflamed tissue. We studied the effect of single-pulse modality Er:YAG on Pseudomonas aeruginosa biofilm removal. We used different laser energies, fiber-tip positions, and laser treatment durations. The cleaning process was monitored in real-time with a high-speed camera after each individual laser pulse application. The obtained results suggest that biofilm cleaning efficacy in a difficult-to-reach place in healthy model tissue is directly related to the onset of secondary cavitation bubble formation, which correlates with a significant improvement of biofilm removal from the apical region of the periodontal or peri-implant pocket. In comparison to the healthy tissue model, the laser energy in inflamed tissue model had to be increased to obtain comparable biofilm cleaning efficacy. The advantage of photoacoustic cavitation compared to other methods is that laser-induced cavitation can trigger secondary cavitation at large distances from the point of laser application, which in principle allows biofilm removal at distant locations not reachable with a laser fiber tip or other mechanical instruments.

Laser direct overall water splitting for H2 and H2O2 production

Hydrogen (H2) and hydrogen peroxide (H2O2) play crucial roles as energy carriers and raw materials for industrial production. However, the current techniques for H2 and H2O2 production rely on complex catalysts and involve multiple intermediate steps. In this study, we present a straightforward, environmentally friendly, and highly efficient laser-induced conversion method for overall water splitting to simultaneously generate H2 and H2O2 at ambient conditions without any catalysts. The laser direct overall water splitting approach achieves an impressive light-to-hydrogen energy conversion efficiency of 2.1%, with H2 production rates of 2.2 mmol/h and H2O2 production rates of 65 µM/h in a limited reaction area (1 mm2) within a short real reaction time (0.36 ms/h). Furthermore, we elucidate the underlying physics and chemistry behind the laser-induced water splitting to produce H2 and H2O2. The laser-induced cavitation bubbles create an optimal microenvironment for water-splitting reactions because of the transient high temperatures (104 K) surpassing the chemical barrier required. Additionally, their rapid cooling rate (1010 K/s) hinders reverse reactions and facilitates H2O2 retention. Finally, upon bubble collapse, H2 is released while H2O2 remains dissolved in the water. Moreover, a preliminary amplification experiment demonstrates the potential industrial applications of this laser chemistry. These findings highlight that laser-based production of H2 and H2O2 from water holds promise as a straightforward, environmentally friendly, and efficient approach on an industrial scale beyond conventional chemical catalysis.

Exploring viscosity influence mechanisms on coating removal: Insights from single cavitation bubble behaviours in low-frequency ultrasonic settings

The role of acoustic cavitation in various surface cleaning disciplines is important. However, the physical mechanisms underlying acoustic cavitation-induced surface cleansing are poorly understood. This is due to the combination of microscopic and ultrashort timescales associated with the dynamics of acoustic cavitation bubbles. Here, we have precisely controlled single-bubble cavitation in both space and time. Ultrasonic excitation leads to the cavitation of generated single bubbles. A synchronous ultrafast photomicrographic system simultaneously records the dynamics of single acoustic cavitation bubbles (SACBs) and the cleaning process of the nearby surface in liquids with varying viscosities. Finally, we analysed the correlation between bubble dynamics and surface cleaning situations. The differences in the typical dynamic characteristics of the bubbles during collapse in liquids with varying viscosities reveal two main mechanisms underlying surface cleaning by acoustic cavitation, which are respective the Laplace pressure during the bubble’s movement and liquid jets during bubble collapse. Our study provides a better physical understanding of the ultrasonic cleaning process based on acoustic cavitation, and will help to optimize and facilitate the applications of surface cleaning, especially for the cleaning of substrates with tightly attached dirt.

Unveiling Fundamentals of Multi-Beam Pulsed Laser Ablation in Liquids toward Scaling up Nanoparticle Production.

Pulsed laser ablation in liquids (PLAL) is a versatile technique to produce high-purity colloidal nanoparticles. Despite considerable recent progress in increasing the productivity of the technique, there is still significant demand for a practical, cost-effective method for upscaling PLAL synthesis. Here we employ and unveil the fundamentals of multi-beam (MB) PLAL. The MB-PLAL upscaling approach can bypass the cavitation bubble, the main limiting factor of PLAL efficiency, by splitting the laser beam into several beams using static diffractive optical elements (DOEs). A multimetallic high-entropy alloy CrFeCoNiMn was used as a model material and the productivity of its nanoparticles in the MB-PLAL setup was investigated and compared with that in the standard single-beam PLAL. We demonstrate that the proposed multi-beam method helps to bypass the cavitation bubble both temporally (lower pulse repetition rates can be used while keeping the optimum processing fluence) and spatially (lower beam scanning speeds are needed) and thus dramatically increases the nanoparticle yield. Time-resolved imaging of the cavitation bubble was performed to correlate the observed production efficiencies with the bubble bypassing. The results suggest that nanoparticle PLAL productivity at the level of g/h can be achieved by the proposed multi-beam strategy using compact kW-class lasers and simple inexpensive scanning systems.

Charged Cavitation Multibubbles Dynamics Model: Growth Process

The nonlinear dynamics of charged cavitation bubbles are investigated theoretically and analytically in this study through the Rayleigh–Plesset model in dielectric liquids. The physical and mathematical situations consist of two models: the first one is noninteracting charged cavitation bubbles (like single cavitation bubble) and the second one is interacting charged cavitation bubbles. The proposed models are formulated and solved analytically based on the Plesset–Zwick technique. The study examines the behaviour of charged cavitation bubble growth processes under the influence of the polytropic exponent, the number of bubbles N, and the distance between the bubbles. From our analysis, it is observed that the radius of charged cavitation bubbles increases with increases in the distance between the bubbles, dimensionless phase transition criteria, and thermal diffusivity, and is inversely proportional to the polytropic exponent and the number of bubbles N. Additionally, it is evident that the growth process of charged cavitation bubbles is enhanced significantly when the number of bubbles is reduced. The electric charges and polytropic exponent weakens the growth process of charged bubbles in dielectric liquids. The obtained results are compared with experimental and theoretical previous works to validate the given solutions of the presented models of noninteraction and interparticle interaction of charged cavitation bubbles.

Influence of interactions between bubbles on physico-chemical effects of acoustic cavitation

Ultrasound technology has been extensively used as one of the efficient and economic methodology to achieve the desired outcomes in many applications by harnessing the physico-chemical effects of acoustic cavitation. However, the cavitation-associated effects, primarily determined by the oscillatory dynamics of cavitation bubbles, are considerably complex and still remain poorly understood. The main objective of this study was to perform a numerical analysis of the acoustic cavitation (i.e., the cavitation dynamics, the resultant temperature, pressure and chemical yields within collapsing bubbles), particularly focusing on the influence of the interactions between bubbles. A comprehensive model was developed to simulate the acoustic cavitation dynamics via combining the influences of mass transfer, heat conduction and chemical reactions as well as the interaction effects between bubbles. The results demonstrated that only the large bubble exerts a greater impact on the small one in a two-bubble system. Specifically, within parameter ranges covered this study, there are noticeable decreases in the expansion ratio of the small bubble, the resultant temperature, pressure and molar yields of free radicals, hence weakening the cavitation intensity and cavitation- associated physico-chemical effects. Moreover, the influences of the interactions between bubbles were further assessed quantitatively under various parameters, such as the ultrasound amplitude PA and frequency f, the distance between bubbles d0, the initial radius of the large bubble R20, as well as the liquid properties (e.g., surface tension σ and viscosity μ). It was found that the suppression effect can be amplified when subjected to ultrasound with an increased PA and/or a decreased f, probably due to a stronger cavitation intensity under this condition. Additionally, the suppression effect is also enhanced with a decrease in d0, σ and μ, but with R20 increasing. This study can contribute to deepening knowledge about acoustic cavitation and the resultant physical and/or chemical effects, potentially further facilitating the ultrasound-assisted various applications involving acoustic cavitation.

Synthesis of Nickel-Based Nanoparticles by Pulsed Laser Ablation in Liquids: Correlations between Laser Beam Power, Size Distribution and Cavitation Bubble Lifetime

Pulsed laser ablation in liquids (PLAL) is a colloidal synthesis technique attracting significant interest from the scientific community due to the quality of the nanoparticles being produced. In this type of synthesis protocol, the cavitation bubble plays a vital role during the synthesis of nanoparticles. This work studied the effect of the laser beam power on cavitation bubble lifetime. Three different laser beam power values (5.8 W, 7.5 W and 10.5 W) were used to irradiate a pure nickel target in de-ionized (DI) water to synthesize nickel-based nanoparticles. The optimal repetition rate maximizing the production of nanoparticles was determined by atomic emission spectroscopy for each laser beam power. It was determined that the optimal repetition rate increased exponentially with laser beam power, while the cavitation bubble lifetime decreased logarithmically with the laser beam power. Moreover, the effect of the laser beam power on the cavitation bubble lifetime also had an effect on the size distribution of the nanoparticles being produced; the smallest size distribution was obtained at the highest laser beam power.

Ophthalmic surgeries on post mortem porcine eyes with picosecond ultrashort laser pulses.

This work demonstrates significant advantages in ophthalmic surgeries through the use of picosecond ultrashort laser pulses instead of state-of-the-art nanosecond laser pulses. These ultrashort lasers shall serve as universal tools more effectively combining advantages of high precision, low impact and economic advantages compared to existing instruments. As samples, we used post-mortem porcine eyes on which we performed the experiments with both picosecond and nanosecond lasers. Performed surgeries were laser iridotomy, (post-) cataract treatment/capsulotomy and selective laser-trabeculoplasty. Pulse widths were between 12 ps and 220 ns with pulse energies between 30 μJ and 10 mJ at 532 nm and 1,064 nm. Additionally, we investigated accompanying shock waves, cavitation bubbles, and heat effects during the ablation processes. For all surgeries, significant differences were observed between picosecond and nanosecond pulses: It was possible to scale the pulse energy down to 10 of microjoules rather than requiring millijoules, and resulting tissue ablations are much more precise, more deterministic and less frayed. The shock wave and cavitation bubble investigation revealed major differences in pressure between picosecond pulses (0.25 MPa, 50 μJ) and nanosecond pulses (37 MPa, 5 mJ). The heat input during ablation could be lowered by two orders of magnitude. Picosecond ultrashort laser pulses show substantial benefits for several ophthalmic surgeries, with regard to ablation precision, shock wave generation and heat input. They are better than state-of-the-art ophthalmic nanosecond lasers in all aspects tested.

Cavitation bubble collapse near a rigid wall with an oil layer

This paper reports on the study of a laser-generated cavitation bubble in water collapsing near a rigid wall that is covered with a layer of silicone oil. The oil viscosity is between 5 and 5000 cSt. It is known that a collapsing cavitation bubble near a rigid boundary develops a jet. In this study, we show that the viscous oil layer competes with the flow generated by the bubble, and affects the short- and long-term bubble dynamics. For very low viscosity silicone oil (5, 10 and 20 cSt) the vortices formed when the water jet hits the wall result in a gas–water mixture in the oil layer. With increasing viscosity, i.e. 50 and 100 cSt, the formation of water droplets with gas bubbles inside the oil layer is observed. The bubble dynamics and flow in the oil layer are nicely reproduced with VoF simulations up to the second bubble collapse. In higher viscosity silicone oils (350, 500 and 1000 cSt), the water jet typically retracts completely during the re-expansion of the bubble. When a very high viscosity oil (5000 cSt) is used, a ‘mushroom’-shaped bubble is formed in water which splits in two as it collapses. To separate the regimes, we introduce a non-dimensional stress ratio relating the inertia and viscosity. This inverse Reynolds number Π becomes approximately 1 in the jet retraction regime. When Π≥ 1.0, the jet impact and vortices are effectively hindered on the rigid wall.

Effects of destruction of Euglena gracilis by ultrasonic cavitation

Euglena gracilis has attracted attention because it contains the polysaccharide paramylon. In this study, we aimed to destruct E. gracilis by applying ultrasonic cavitation and to elucidate the mechanism. We also examined the breakdown of paramylon particles and attempted to extract paramylon nanofibers. It was suggested that the damage caused by ultrasonic waves was frequency dependent and influenced by the size ratio of the cell to cavitation bubbles, yield strength, and inhibition of cavitation bubble growth in suspension. It is also assumed that the cell destruction rate decreased because it was also dependent on the initial cell density, and an increase in the initial cell density resulted in a decrease in acoustic pressure. The fracture strength of the paramylon particles was much greater than the microjet stress at the acoustic power used in this study, and the paramylon particles did not fracture.

Predicting shock-induced cavitation using machine learning: implications for blast-injury models.

While cavitation has been suspected as a mechanism of blast-induced traumatic brain injury (bTBI) for a number of years, this phenomenon remains difficult to study due to the current inability to measure cavitation in vivo. Therefore, numerical simulations are often implemented to study cavitation in the brain and surrounding fluids after blast exposure. However, these simulations need to be validated with the results from cavitation experiments. Machine learning algorithms have not generally been applied to study blast injury or biological cavitation models. However, such algorithms have concrete measures for optimization using fewer parameters than those of finite element or fluid dynamics models. Thus, machine learning algorithms are a viable option for predicting cavitation behavior from experiments and numerical simulations. This paper compares the ability of two machine learning algorithms, k-nearest neighbor (kNN) and support vector machine (SVM), to predict shock-induced cavitation behavior. The machine learning models were trained and validated with experimental data from a three-dimensional shock tube model, and it has been shown that the algorithms could predict the number of cavitation bubbles produced at a given temperature with good accuracy. This study demonstrates the potential utility of machine learning in studying shock-induced cavitation for applications in blast injury research.

Investigation of the influence of different liquid temperatures on the dynamics of long-pulse laser-induced cavitation bubbles

Long-Pulse Laser-induced cavitation bubbles have been identified to hold significant applications in various fields, such as industry and medicine. In this study, the dynamics of cavitation bubbles, induced by a 2.94 μm wavelength Er:YAG laser with an energy of 20 ±1 mJ and transmitted via sapphire fiber optics into distilled water at different temperatures, were investigated. The adiabatic expansion theory was utilized to predict the maximum length (Lmax) and the maximum width (Wmax) of the cavitation bubbles at different liquid temperatures. Excellent alignment was observed between the theoretical predictions and the experimental data. Using this theory, the local overheated liquid temperature was deduced to be ∼180 °C during the formation of cavitation bubbles. It was found that as the liquid temperature increased, the collapse position of the cavitation bubbles, relative to the normalized distance (γ) from the fiber end face, decreased. This study reveals the importance of considering the potential risk of damage to fiber optics from the shockwaves and microjet streams generated by cavitation bubbles in high-temperature conditions.

Experimental study on cavitation inhibition in a butterfly valve with different plate shapes

A valve is a kind of mechanical device used to control the flow of fluid in pipelines or systems, which has a wide range of uses in various industrial, commercial, and household applications. When the fluid passes through the valve, cavitation often occurs in the valve, resulting in the valve not working properly and even damaging the valve and related systems. In this paper, experimental visualization was used to investigate cavitation evolution through a butterfly valve with different plate shapes under different pressure conditions. The results show that with the increase in the curvature of both sides of the butterfly plate and the increase in the total pressure condition, the cavitation type inside the butterfly valve will change from non-attached cavitation to attached cavitation. In addition, the maximum length and thickness of the attached cavitation bubbles gradually increase as well. However, when the shape of both ends of the butterfly plate is triangular, the adhesion ability to cavitation bubbles is greatly reduced. As the curvature increases, the frequency of the shedding of cavitation bubble gradually decreases, the volume of cavitation bubble increases, and the shedding of the cavitation bubble caused by the shock wave is more obvious. When the shape of both sides of the butterfly plate is triangular, the position where the bubble collapses is closer to the front end of the butterfly plate, and the shock wave generated by the bubble collapse will lead to the collapse of the attached cavitation bubble.

Collapsing behavior of spark-induced cavitation bubble in rigid tube

The phenomenon of cavitation within tubes is a common scenario in the fields of medicine and industry. This paper focuses on the effects of rigid circular tube length, diameter and the distance of bubble - tube port on the behavior of bubble in tube. The low-voltage discharge technique was utilized to induce a cavitation bubble in deionized water. The effects of rigid tube lengths, diameters, and bubble-tube port distances on the morphology of bubbles are observed using high-speed camera. It has been found that as the length of the rigid tube increases, so does the period, and this effect is more pronounced in tubes with smaller diameters. Conversely, the cavitation bubble period decreased and then stabilized as the tube diameter increased, the ratio of tube radius and the bubble radius exceeds 4.8, the period of bubble in tube is similar to that of bubble in free field. Further analysis of the influence of tube characteristics on microjets reveals that a pair of oppositely microjets were formed along the tube axis by the bubble near the midpoint of the tube axis. Moreover, when the non-dimensional tube length η < 3.5, the increase tube diameter results in a decrease microjet velocity. It has also been observed that as the bubble gradually approaches the interior of the tube, the velocity of microjets directed inward decreases. Additionally, the smaller the diameter of the tube, the greater the bubble-tube port distance required for the microjets to reach the same level of velocity as bubble near the center of the tube axis. These findings hold theoretical implications for improvement of targeted drug delivery efficiency in medicine and enhance the operational efficiency of inertial micropumps in industries.

Research on cavitation bubble behaviors between a dual-particle pair

The interactions between particle clusters and cavitation bubbles play an important role in several industrial applications, e.g., the abrasive erosion of hydraulic machinery, the efficiency improvement of ultrasonic cleaning, and the mineral flotation. This paper explores the influence of a dual-particle pair of unequal sizes on the bubble collapse dynamics based on a Kelvin impulse model and high-speed photography. The impact of the radius ratio of the dual-particle pair (ranging from 1.0 to 3.0), defined as the ratio of the large-particle radius to the small-particle radius, on the bubble interface deformation, collapse jet, and the translational movement of the bubble is analyzed. The main findings are as follows: (1) the Kelvin impulse based on the Weiss theorem can effectively predict the asymmetric bubble behaviors in terms of the moving distance and the direction of the bubble centroid during the bubble collapse; (2) the particle radius ratio is a key parameter affecting the intensity and direction of the Kelvin impulse, as well as the bubble centroid moving distance; and (3) the zero-Kelvin-impulse point is always biased toward the smaller particle in the dual-particle pair.