Behavior Of Cavitation Bubbles Research Articles

Lattice Boltzmann Simulation of Cavitation and Particle Behavior Induced by Sonication Transducer

In the semiconductor process, cleaning wafer surface by megasonic transducer with thin liquid film is getting more attention than conventional bath-type batch cleaner. Although its major contribution to the cleaning process, nanoparticle removal mechanism of megasonic cleaning is not fully understood yet. Thus the understanding of the cavitation bubble motion formed by megasonic wave is very important. Due to rapid motion of the bubbles experimental observation of their movement is hard to achieve. In present study, we introduce lattice Boltzmann method to simulation fluid and cavitation bubble behavior. Validation was achieved by compare the simulation result with analytical solution of fluid motion. It was shown that bubbles formed by cavitation phenomena can be expanded, shrunken, or even collapsed to emit shockwave.

Numerical Assessment of Hydrodynamic Cavitation Reactors Using Organic Solvents

This paper attempts to give a physical insight into the behavior of cavitation bubbles in a hydrodynamic cavitation reactor, with organic liquids employed as the bulk medium. The diffusion limited model of cavitation bubble dynamics has been coupled to hydrodynamics of flow through an orifice. Two kinds of bubbles, namely, air and argon, and two organic liquids, namely, n-hexane and toluene, have been chosen as the model system. The effect of four parameters on the dynamics of cavitation bubbles, namely, cavitation number, orifice to pipe diameter ratio, downstream recovery pressure, and initial bubble radius, has been investigated. Simulations show interesting results that dynamics of cavitation bubbles in organic media is relatively insensitive to operating parameters. These results have been attributed to physical properties of the organic media. Relatively, the intensity of the collapse of bubbles in toluene is higher than in hexane; however, the temperature peaks attained at the transient collapse of...

Dynamical behaviors of hydrodynamic cavitation bubble under ultrasound field

Considering liquid viscosity, surface tension, liquid compressibility and turbulence, the dynamical behaviors of cavitation bubble in venturi cavitation reactor are numerically investigated with using acoustic field regarding water as a work medium. The effects of acoustic frequency, acoustic pressure and ratio of throat to pipe diameter on cavitation bubble dynamics, bubble temperature and pressure pulse by rapid collapse of cavitation bubble are analysed. The results show that bubble motion of hydrodynamic cavitation modulated by ultrasound, becomes the high energy stable cavitation. It is favorable for enhancing the cavitation effect.

A new approach to nucleation of cavitation bubbles at chemically modified surfaces

Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm(-2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation.

湍流作用下可压缩液体中空化泡的动力学特性

Considering such factors as liquid viscosity, surface tension, liquid compressibility and turbulence, the dynamical behaviors of cavitation bubble in orifice plate hydrodynamic cavitation reactor are numerically investigated regarding water as work medium. Detailed analysis is conducted to understand the effects of turbulence, initial radius of cavitation bubble, downstream recovery pressure of the orifice plate, pipe diameter and orifice to pipe diameter ratio on the cavitation bubble dynamics and the pressure pulse caused by rapid shrinkage of cavitation bubble. Some new phenomena such as second growth of cavitation bubble radius are discovered. The achievements obtained in this work may provide theoretical guidance and technical support for the optimization design of hydrodynamic cavitation reactor and practical application of hydrodynamic cavitation technology.

Dynamic behaviors of cavitation bubble for the steady cavitating flow

In this paper, by introducing the flow velocity item into the classical Rayleigh-Plesset dynamic equation, a new equation, which does not involve the time term and can describe the motion of cavitation bubble in the steady cavitating flow, has been obtained. By solving the new motion equation using Runge-Kutta fourth order method with adaptive step size control, the dynamic behaviors of cavitation bubble driven by the varying pressure field downstream of a venturi cavitation reactor are numerically simulated. The effects of liquid temperature (corresponding to the saturated vapor pressure of liquid), cavitation number and inlet pressure of venturi on radial motion of bubble and pressure pulse due to the radial motion are analyzed and discussed in detail. Some dynamic behaviors of bubble different from those in previous papers are displayed. In addition, the internal relationship between bubble dynamics and process intensification is also discussed. The simulation results reported in this work reveal the variation laws of cavitation intensity with the flow conditions of liquid, and will lay a foundation for the practical application of hydrodynamic cavitation technology.

Multibubble cavitation inception

The inception of cavitation in multibubble cases is studied numerically and theoretically to show that it is different from that in single-bubble cases in several aspects. Using a multibubble model based on the Rayleigh–Plesset equation with an acoustic interaction term, we confirmed that the recently reported suppression of cavitation inception due to the interaction of nonidentical bubbles can take place not only in liquid mercury but also in water, and we found that a relatively large bubble can significantly decrease the cavitation threshold pressure of a nearby small bubble. By examining in detail the transition region where the dynamics of the suppressed bubble changes drastically as the interbubble distance changes, we determined that the explosive expansion of a bubble under negative pressure can be interrupted and turn into collapse even though the far-field liquid pressure well exceeds the bubble’s threshold pressure. Numerical results suggest that the interruption of expansion occurs when the bubble radius is exceeded by the instantaneous unstable equilibrium radius of the bubble determined using the total pressure acting on the bubble. When we extended the discussion to systems of larger numbers of bubbles, we found that a larger number of bubbles have a stronger suppression effect. The present findings would be useful in understanding the complex behavior of cavitation bubbles in practical applications where, in general, many cavitation nuclei exist and may interact with each other.

Cavitation Bubbles Mediated Molecular Delivery During Sonoporation

Molecular delivery using ultrasound (US) and nano/microbubbles (NBs), i.e., sonoporation, has applications in gene therapy and anticancer drug delivery. When NBs are destructed by ultrasound, the surrounding cells are exposed to mechanical impulsive forces generated by collapse of either the NBs or the cavitation bubbles created by the collapse of NBs. In the present study, experimental, theoretical and numerical analyses were performed to investigate cavitation bubbles mediated molecular delivery during sonoporation. Experimental observation using lipid NBs indicated that increasing US pressure increased uptake of fluorescent molecules, calcein (molecular weight: 622), into 293T human, and decreased survival fraction. Confocal microscopy revealed that calcein molecules were uniformly distributed throughout the some treated cells. Next, the cavitation bubble behavior was analyzed theoretically based on a spherical gas bubble dynamics. The impulse of the shock wave (i.e., the pressure integrated over time) generated by the collapse of a cavitation bubble was a dominant factor for exogenous molecules to enter into the cell membrane rather than bubble expansion. Molecular dynamics simulation revealed that the number of exogenous molecules delivered into the cell membrane increased with increasing the shock wave impulse. We concluded that the impulse of the shock wave generated by cavitation bubbles was one of important parameters for causing exogenous molecular uptake into living cells during sonoporation.

Optimisation of sludge disruption by sonication

This study presents an examination on the correlation of sonication operating condition, sludge property, formation and behaviour of cavitation bubbles in sludge disruption under low-frequency ultrasound sonication. The influence of sonication time, sonication density, type of sludge and solids content on the disruption was evaluated. The most vigorous particle disruption was achieved in the initial period of sonication, which subsided subsequently. The explosive effect was likely due to the rapid cavitation arising from powerful transient bubbles generated in fractions of microseconds. A rating for the type of sludge was derived based on the finding that particles in secondary sludge were more readily disrupted than both primary sludge and mixed sludge. While sonication density exhibited the most significant role in cavitation bubble formation and behaviour, particle disruption could be optimised for energy input by sonicating at higher sonication density and shorter sonication time. Based on theoretical consideration, it was deduced that within an optimum sludge solids content ranging between 2.3% and 3.2%, superior particle disruption could be accomplished within a minute for secondary sludge sonicated at a density of 0.52 W/mL. Useful guidelines for sonication system installation, equipment protection and process reliability could be established from knowledge derived from a good understanding on the influence of solids content on sludge sonication.

Stochastic study of cavitation bubbles near boundary wall

Abstract A proposed Markov stochastic model for the random behavior of cavitation bubble(s) near compliant walls is introduced. Also for verification of the model a versatile facility for observing the effects of wall compliance on the stochastic behavior of single/multi-bubbles has been designed and built purposely at the Fluid Dynamics Research Centre, the University of Warwick (UK). This paper briefly intro- duces the previous work and the testing facility as well as current on going work.

Transfection effect of microbubbles on cells in superposed ultrasound waves and behavior of cavitation bubble

The combination of ultrasound and ultrasound contrast agents (UCAs) is able to induce transient membrane permeability leading to direct delivery of exogenous molecules into cells. Cavitation bubbles are believed to be involved in the membrane permeability; however, the detailed mechanism is still unknown. In the present study, the effects of ultrasound and the UCAs, Optison™ on transfection in vitro for different medium heights and the related dynamic behaviors of cavitation bubbles were investigated. Cultured CHO-E cells mixed with reporter genes (luciferase or β-gal plasmid DNA) and UCAs were exposed to 1MHz ultrasound in 24-well plates. Ultrasound was applied from the bottom of the well and reflected at the free surface of the medium, resulting in the superposition of ultrasound waves within the well. Cells cultured on the bottom of 24-well plates were located near the first node (displacement node) of the incident ultrasound downstream. Transfection activity was a function determined with the height of the medium (wave traveling distance), as well as the concentration of UCAs and the exposure time was also determined with the concentration of UCAs and the exposure duration. Survival fraction was determined by MTT assay, also changes with these values in the reverse pattern compared with luciferase activity. With shallow medium height, high transfection efficacy and high survival fraction were obtained at a low concentration of UCAs. In addition, capillary waves and subsequent atomized particles became significant as the medium height decreased. These phenomena suggested cavitation bubbles were being generated in the medium. To determine the effect of UCAs on bubble generation, we repeated the experiments using crushed heat-treated Optison™ solution instead of the standard microbubble preparation. The transfection ratio and survival fraction showed no additional benefit when ultrasound was used. These results suggested that cavitation bubbles created by the collapse of UCAs were a key factor for transfection, and their intensities were enhanced by the interaction of the superpose ultrasound with the decreasing the height of the medium. Hypothesizing that free cavitation bubbles were generated from cavitation nuclei created by fragmented UCA shells, we carried out numerical analysis of a free spherical bubble motion in the field of ultrasound. Analyzing the interaction of the shock wave generated by a cavitation bubble and a cell membrane, we estimated the shock wave propagation distance that would induce cell membrane damage from the center of the cavitation bubble. (E-mail: kodama@tubero.tohoku.ac.jp)

Deformation of a Single Bubble with Ultrasonic Irradiation

The behavior of cavitation bubbles is important in sonoplasma, which is generated by simultaneous microwave and ultrasound irradiation. Sonoplasma is expected to be applied in great many fields, such as high-speed chemical vapor deposition. In this study, the behavior of a single bubble in n-dodecane with ultrasonic irradiation was first observed using a charge-coupled-device camera and a stroboscope. In the observation, though sonoluminescence was not confirmed, the bubble was expanded and contracted synchronously with the ultrasonic frequency and was deformed when it contracted to its minimum size. The mechanism of the deformation of the bubble was clarified by numerical analysis. The stability of the bubble can be determined according to initial radius and the amplitude of the sound pressure.

Effect of Ultrasonic Cavitation on Force Acting on Solid Object in Water

Attractive force or repulsive force acts on solid objects facing an ultrasonically vibrating horn in liquid. Severe cavitation damage is observed on the surface of an aluminum plate adhereing to an ultrasonically vibrating horn in water. To elucidate the mechanisms of the generation of force acting on a solid object in a near ultrasonic field in water, the behavior of cavitation bubbles on the surfaces of an ultrasonically vibrating horn and a solid object was investigated. From the results of in situ observation, it was clarified that the force acting on a solid object is controlled by bubble generation and collapse.

A non‐invasive tissue‐specific molecular delivery method of cancer gene therapy

A Japanese word, monozukuri (literally translated “making things”) is the philosophy of first having the idea and then the faith in the technical expertise and experience to accomplish the result. We believe that the concept of engineering is monozukuri. Through the process of monozukuri, engineered natural science based on mathematics and physics has been developed. Medicine is the field of study which has been developed for maintaining daily healthy life with diagnosis, treatment, examination, and protection. Biomedical engineering is the interdisciplinary study of engineering and medicine, and should be developed based on monozukuri. In this particular research, we have developed a physical molecular delivery method for cancer gene therapy using nano/microbubbles and ultrasound. First, the behavior of cavitation bubbles and subsequent shock wave phenomena involved in the mechanism of molecular delivery were analyzed, combining theory and computer simulation. In a second step, the methodology was optimized in vitro and in vivo. Finally, the therapeutic potential of the method in pre‐clinical models was evaluated using transgenes relevant to cancer gene therapy instead of reporter genes, and whole body, non‐invasive imaging using single photon emission computed tomography (SPECT/CT) was used to evaluate the selectivity of gene delivery in vivo.

803 がん遺伝子治療を目指した非侵襲撃組織標的性分子導入法の開発(1)(OS8-1 医療援用工学における流動ダイナミクス,OS8 医療援用工学における流動ダイナミクス,オーガナイズドセッション)

Gene transfer to cancer cells using nanobubbles (NBs) and ultrasound (US) is a non-invasive gene therapy. In order to improve efficacy of gene transfection, the impulsive pressures generated by cavitation bubbles created by the collapse of NBs have to be optimized. In addition, the mechanism of molecular transfer as d as subsequent therapeutic effect has to be investigated. In the present study, we delivered fluorescence molecules into cells with the NB-US method and quantified the intracellular fluorescence molecules. Next we verified the therapeutic effect of suicide gene therapy in vitro using harpes simplex virus thymidine kinase (HSV tk) gene and ganciclovir (GCV), Finally we analyzed the cavitation bubble behavior and the interaction of the shock wave with a lipid bilayer by using theoretical and numerical methods, We attributed the delivery exogenous molecules by the NS-US method to the structural change in the lipid bilayer caused by the interaction of the shock waves from the cavitation bubbles.

803 がん遺伝子治療を目指した非侵襲撃組織標的性分子導入法の開発(2)(OS8-1 医療援用工学における流動ダイナミクス,OS8 医療援用工学における流動ダイナミクス,オーガナイズドセッション)

Gene transfer to cancer cells using nanobubbles (NBs) and ultrasound (US) is a non-invasive gene therapy. In order to improve efficacy of gene transfection, the impulsive pressures generated by cavitation bubbles created by the collapse of NBs have to be optimized. In addition, the mechanism of molecular transfer as d as subsequent therapeutic effect has to be investigated. In the present study, we delivered fluorescence molecules into cells with the NB-US method and quantified the intracellular fluorescence molecules. Next we verified the therapeutic effect of suicide gene therapy in vitro using harpes simplex virus thymidine kinase (HSV tk) gene and ganciclovir (GCV), Finally we analyzed the cavitation bubble behavior and the interaction of the shock wave with a lipid bilayer by using theoretical and numerical methods, We attributed the delivery exogenous molecules by the NS-US method to the structural change in the lipid bilayer caused by the interaction of the shock waves from the cavitation bubbles.

A model for the dynamics of gas bubbles in soft tissue

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. Keller-Miksis equation, which can account for the large amplitude oscillations of bubbles, is rederived in this paper and combined with a viscoelastic model to account for the strain-stress relation. The viscoelastic model used in this study is the Voigt model. It is shown that only the viscous damping term in the original equation needs to be modified to account for the effect of elasticity. With experiment determined viscoelastic properties, the effects of elasticity on bubble oscillations are studied. Specifically, the inertial cavitation thresholds are determined using R(max)/R(0), and subharmonic signals from the emission of an oscillating bubble are estimated. The results show that the presence of the elasticity increases the threshold pressure for a bubble to oscillate inertially, and subharmonic signals may only be detectable in certain ranges of radius and pressure amplitude. These results should be easy to verify experimentally, and they may also be useful in cavitation detection and bubble-enhanced imaging.

Nonlinear dynamics of gas bubbles in viscoelastic media

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. The Keller–Miksis equation for nonlinear bubble dynamics is combined with the Voigt model for viscoelastic media. Using experimentally determined values, the effects of elasticity on bubble oscillations are studied. Inertial cavitation thresholds are determined using Rmax/R0=2, and subharmonic emissions are also estimated. The elasticity increases the threshold pressure for inertial cavitation, and subharmonic signals are significant only in a certain region of radii and driving pressures at a given frequency. These results should prove useful in cavitation detection and bubble-enhanced imaging work.

Nonlinear dynamics of gas bubbles in soft tissue

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. The previous studies are largely limited by availability of experimental data on soft tissue. To approach this problem, we combine the Keller-Miksis equation for nonlinear bubble dynamics with the linear Voigt model for viscoelastic media. Using experimentally determined values of viscoelastic properties of soft tissue as a guide, the effects of elasticity on bubble oscillations are studied. The inertial cavitation thresholds are determined using a criterion of Rmax/R0=2, and subharmonic emissions from an oscillating bubble are calculated. The results show that the presence of the elasticity increases the threshold pressure for inertial cavitation, and subharmonic signals only can be detected in a certain region of radii and driving pressures at a given frequency. These results should be useful in cavitation detection and bubble-enhanced imaging work. The model also could be used to determine values for the viscoelastic properties of soft tissue.

Modeling of initial bubble growth rates during high-intensity focused ultrasound

In therapeutic applications of biomedical ultrasound, it is important to understand the behavior of cavitation bubbles. For applications that use high-intensity focused ultrasound (HIFU), both large negative acoustic pressures and heating can independently lead to bubble formation. Although neglected previously, heating during HIFU is expected to affect the growth and dissolution of bubbles by both raising the vapor pressure and promoting outgassing from gas-saturated tissues. Herein, the dynamics of a single, spherical bubble in water have been modeled using the Gilmore equation closed with an energy balance on bubble contents for calculation of pressures inside the bubble. Moreover, heat and mass transfer at the bubble wall are incorporated using the Eller-Flynn zeroth-order approximation for gas diffusion, an estimation of non-equilibrium phase change based on the kinetic theory of gases, and assumed shapes for the spatial temperature distribution in the surrounding liquid [Yasui, J. Phys. Soc. Jpn. 65, 2830–2840 (1996)]. This model allows explicit coupling of the ambient heating during HIFU to the thermodynamic state of an oscillating bubble and is currently being used to explore the growth rates of initially small, undetectable bubbles exposed to various HIFU treatment protocols. [Work supported by NIH T32-EB-001650, NIH DK43881, and NSBRI SMS00203.]