Cavitation Bubble Dynamics Research Articles

Experimental study of influences of a particle on the collapsing dynamics of a laser-induced cavitation bubble near a solid wall

In the present paper, the collapsing dynamics of a laser-induced cavitation bubble between a spherical particle and a solid wall is fully revealed using a high-speed camera based cavitation experimental system. For the purpose of comparisons, experiments of cases without the presence of the particle are also conducted and demonstrated. Influences of several paramount parameters (including the bubble radius, the particle radius, and the relative positions among the bubble, the particle and wall) on the bubble collapsing dynamics, the motions of bubble boundaries and the positions of the bubble centroid are all investigated. Based on the directions of the micro-jets during the bubble collapse, the bubble collapsing behavior could be categorized into three cases with their primary characteristics revealed. Furthermore, the transitions among three different cases are clearly demonstrated using several examples in terms of high-speed photography. Based on a large amount of experimental data, quantitative discussions on the parameter zone of the identified three typical cases are given in terms of the three non-dimensional parameters. Generally speaking, the particle scale does not show significant influences on the bubble dynamics behavior except some special positions of the bubble.

Experimental investigations of the particle motions induced by a laser-generated cavitation bubble

The interactions between a laser-generated cavitation bubble and a spherical particle are investigated experimentally with the aid of high-speed camera. Both the cavitation bubble dynamics and its induced particle moving dynamics are clearly recorded and analyzed qualitatively and quantitatively. Influences of two essential parameters (including the bubble-particle distance and the particle/bubble radius ratio) on the phenomenon are given and discussed. Furthermore, the underlying physical mechanisms are discussed based on the calculations of the radiation pressure and the generations of the micro-jet. Our results reveal that the distance between the cavitation bubble and the particle shows significant influences on the phenomenon. For different radius ratios, the maximum particle displacement varies especially for the small stand-off distance.

Dynamics and surface stability of a cylindrical cavitation bubble in a rectilinear vortex

In this paper, we formulate the dynamic equations of radial and surface modes for a cylindrical cavitation bubble subject to a prescribed uniform rectilinear vortex flow. The potential flow in the bulk volume of the external flow is modelled using the general mode decomposition approach. The stability of surface modes is investigated under linear analysis. The effects of confinement due to a limited flow domain in a water tunnel and viscosity at the bubble surface are evaluated, which can be fairly neglected for the cylindrical cavitation bubbles discussed. Our model is capable of predicting the developments of surface modes, which agrees well with experimental observations reported in the literature. We derive the Mathieu structure in the dynamic equation of the surface oscillation and the associated instability condition of the surface mode oscillations. The numerical results confirm that the Mathieu-type instability controls the stability diagrams and the emergence of surface modes under specific radial oscillation.

Numerical Study on the Potential of Cavitation Damage in a Lead⁻Bismuth Eutectic Spallation Target.

To perform basic Research and Development for future Accelerator-driven Systems (ADSs), Japan Proton Accelerator Research Complex (J-PARC) will construct an ADS target test facility. A Lead–Bismuth Eutectic (LBE) spallation target will be installed in the target test facility and bombarded by pulsed proton beams (250 kW, 400 MeV, 25 Hz, and 0.5 ms pulse duration). To realize the LBE spallation target, cavitation damage due to pressure changes in the liquid metal should be determined, preliminarily, because such damage is considered to be very critical, from the viewpoint of target safety and lifetime. In this study, cavitation damage due to pressure waves caused by pulsed proton beam injection and turbulent liquid metal flow, were studied, numerically, from the viewpoint of single cavitation bubble dynamics. Specifically, the threshold of cavitation and effects of flow speed fluctuation on cavitation bubble dynamics, in an orifice structure, were investigated in the present work. The results showed that the LBE spallation target did not undergo cavitation damage, under normal nominal operation conditions, mainly because of the long pulse duration of the pulsed proton beam and the low liquid metal flow velocity. Nevertheless, the possibility of cavitation damage in the orifice structure, under certain extreme transient LBE flow conditions, cannot be neglected.

Numerical investigation of the liquid motion influence on the collapse of a cavitation bubble near a wall

Axially symmetric dynamics of a single cavitation bubble near a plane wall in the process of its expansion and collapse with transformation of the bubble into a toroidal one is considered. The influence of the liquid motion at the end of expansion on the following collapse is studied, depending on the initial distance between the bubble and the wall. The liquid is assumed ideal incompressible, its motion potential. The numerical technique is based on the stepping method of describing the bubble contour movement and the boundary element method. It is shown that with increasing the initial distance between the bubble and the wall, the differences in the shape of the bubble and the liquid pressure at the bubble collapse with and without allowing for the liquid motion at the beginning of collapse significantly decrease.

Interaction of a cavitation bubble with a polymeric coating–scaling fluid and material dynamics

Cavitation bubble dynamics and interaction with a polymeric coating material can be scaled in space and time using spark-generated bubbles near an appropriate soft material and can be simulated using fluid-structure interaction (FSI) modelling. In this paper, cavitation bubble dynamics in a high-pressure cavitating jet eroding a Polyurea layer on a rigid substrate is simulated using spark-generated bubbles operating at reduced pressures near an Agar layer of a properly selected concentration. Geometric scaling is based on the ratio of bubble maximum radii in the two configurations, and fluid dynamics scaling follows the Rayleigh scaling, i.e. lengths are normalized by the bubble maximum radius and times by the Rayleigh time. Scaling of the materials properties is achieved by equating the ratio of the materials mechanical properties (Young's and shear moduli) to the ratio of the local ambient pressures collapsing the bubble. Full FSI numerical simulations conducted at different scales with the two materials indicate the validity of the scaling.

Dynamics and primary breakup of cavitation bubbles under throttling conditions

Cavitation significantly influences fuel mixture preparation and combustion of IC engines which are the main power source of transportation. Investigation of cavitation in injector and its effect on spray breakup is very important for reduction of emissions and fuel consumption. To study the cavitation dynamics and primary breakup, highly resolved microscopic imaging technique was employed with an enlarged transparent nozzle and a real-sized nozzle under various throttling conditions. Mechanisms of cavitation generation were investigated through the cavitation generation locations and morphologies. The characteristics of the secondary vapor bubbles were also probed by injecting diesel into the liquid based on the differences of density and refraction between liquid and vapor. It was found that under low pressure, dynamic cavitation which developed and receded bi-directionally was observed close to the inlet. Cavitation in the sac and nozzle inlet was mainly throttling induced under low pressure and redirection induced under high pressure, while cavitation at nozzle outlet was mainly redirection induced. Increasing pressure strengthened cavitation at both inlet and outlet, and made the vapor bubbles more compact and deformed. Decreasing throttling effect enhanced the cavitation before weakening. Besides, vapor bubbles collapsed very quickly at the nozzle outlet due to the abrupt pressure reduction.

How the re-irradiation of a single ablation spot affects cavitation bubble dynamics and nanoparticles properties in laser ablation in liquids

Fundamental theoretical and experimental studies on the formation of nanoparticles and cavitation during laser synthesis of colloids usually employ single-pulse conditions, whereas studies of the properties of nanoparticles naturally require prolonged ablation. We explored how a defined number of pulses changes a silver target’s surface geometry and thereby the dynamics of the laser-induced cavitation bubble and the resulting properties of the nanoparticles. The shape of the cavitation bubble transforms from hemispherical to almost spherical. The indirectly calculated mass concentration in the cavitation bubble follows a decay with the number of laser pulses. Surprisingly, the ablated mass does not set the volume of the extended cavitation bubble, as one would expect, because of the linear dependency of both the volume of the bubble and the ablation mass per pulse on the laser fluence. No influence of the altered cavitation bubble on the nanoparticles was identified. Instead, clear evidence of a high share of silver nanoclusters (d < 3 nm) with improved instrumentation (ultracentrifuge) was found in all samples at our low concentration conditions. The influence of these reactive species on the final particle size was found to be much larger than the cavitation bubble variations caused by prolonged surface ablation. In addition, no correlation was observed between the size of the primary particles (∼8 nm) and the mass concentration in the cavitation bubble.

Bubble dynamics and its applications

Bubbles have very important applications in many fields such as shipbuilding engineering, ocean engineering, mechanical engineering, environmental engineering, chemical engineering, medical science and so on. In this paper, the research status and the development of the bubble dynamics in terms of theory, numerical simulation and experimental technique are reviewed, which cover the underwater explosion bubble, airgun bubble, spark bubble, laser bubble, rising bubble, propeller cavitation bubble, water entry/exit cavitation bubble and bubble dynamics in other fields. Former researchers have done a lot of researches on bubble dynamics and gained fruitful achievements. However, due to the complexity of the bubble motion, many tough mechanical problems remain to be solved. Based on the research progress of bubble dynamics, this paper gives the future research direction of bubble dynamics, aiming to provide references for researches related to bubble dynamics.

Dynamics of cavitation bubbles formed by pulsed-laser ablation plasmas near the critical point of CO2

The realization of superior reaction fields for the synthesis of nanomaterials with pulsed-laser ablation (PLA) in high-density media, such as liquids, high pressure gases, and supercritical fluids (SCFs), especially near the critical point (CP), and the important role of the formation and evolution of cavitation bubbles for tuning the properties of the nanomaterials have been reported. In this study, to further elucidate the dynamics of the fluid in the stages following PLA, the characteristic behavior of cavitation bubbles formed by PLA plasmas near the CP of CO2 has been investigated using shadowgraph imaging. The time evolution of the cavitation bubbles can be divided into six phases. These include a double-layer structure and a long-time stagnation of the cavitation bubbles, which are peculiar to experimental conditions near the CP. Both spatial and time scale of the cavitation bubbles are at maximum 4–5 times larger near the CP compared to high-pressure liquid and liquid-like SCF far from the CP.

Mechanistic investigations in ultrasound-assisted extraction of astaxanthin from Phaffia rhodozyma MTCC 7536

This study has dealt with physical mechanism of ultrasound-assisted astaxanthin extraction from dry cell mass (DCM) of Phaffia rhodozyma. Preliminary experiments for screening of extraction solvent revealed highest extraction yield for acetone. Further experiments were performed using mixtures of DMSO and acetone with varying compositions as extraction solvent. The results were analyzed in concurrence with prediction of astaxanthin solubility using UNIFAC (Universal Quasi-Chemical Functional-Group Activity Coefficients) method and simulations of cavitation bubble dynamics. The highest astaxanthin yield of 1536 ± 3 μg/g DCM was obtained for solvent comprising 33% v/v DMSO + 67% v/v acetone. UNIFAC predicted astaxanthin solubility (1.57 g/L) was also highest for this composition, although the convection intensity predicted by bubble dynamics simulations was relatively low. Astaxanthin yield reduced with further increase in DMSO volume fraction in solvent. This result has pointed towards dominant role of solubility of solute rather than intensity of convection in extraction mixture in the extraction yield of astaxanthin.

Planar jets in collapsing cavitation bubbles

The dynamics of a laser-induced cavitation bubble generated in the middle of two parallel horizontal rigid walls which are closed at one end with a vertical rigid wall is investigated experimentally using high-speed photography with 100,000 frames s−1. To gain a better understanding of the physical processes that underlie the bubble motion, numerical simulations are conducted by using a boundary element method with an incompressible formulation. We found a complex jetting behaviour which depends strongly on the relative size of the bubble with respect to the distance between the parallel walls and the initial location of the bubble from the vertical rigid wall. When the bubble is generated far from the vertical rigid wall, a radial jet is formed during bubble collapse leading, in some conditions, to bubble splitting. A bubble generated close to the vertical rigid wall develops a planar jet during its collapse phase, which is directed towards the vertical rigid wall. In the transition region, both a radial and a planar jet are generated. When the bubble diameter at its maximum expansion is much smaller than the distance between the parallel rigid walls, both the penetration of the planar jet on the opposite bubble surface and the formation of the secondary cavitation structure were observed during bubble oscillation. The height of the planar jet increases with increasing the bubble size with respect to the distance between the parallel rigid walls. The jet velocity decreases with increasing the relative bubble size with respect to the distance between the horizontal walls and decreasing the initial location of the bubble from the vertical wall. The complex jetting behaviour is attributed to a difference between the strength of the pressure gradients acting on the bubble motion during its collapse phase.

Efficient Propulsion and Hovering of Bubble-Driven Hollow Micromotors underneath an Air-Liquid Interface.

Bubble-driven micromotors have attracted substantial interest due to their remarkable self-motile and cargo-delivering abilities in biomedical or environmental applications. Here, we developed a hollow micromotor that experiences fast self-propulsion underneath an air-liquid interface by periodic bubble growth and collapse. The collapsing of a single microbubble induces a ∼1 m·s-1 impulsive jetting flow that instantaneously pushes the micromotor forward. Unlike previously reported micromotors propelled by the recoiling of bubbles, cavitation-induced jetting further utilizes the energy stored in the bubble to propel the micromotor and thus enhances the energy conversion efficiency by 3 orders of magnitude. Four different modes of propulsion are, for the first time, identified by quantifying the dependence of propulsion strength on microbubble size. Meanwhile, the vertical component of the jetting flow counteracts the buoyancy of the micromotor-bubble dimer and facilitates counterintuitive hovering underneath the air-liquid interface. This work not only enriches the understanding of the propulsion mechanism of bubble-driven micromotors but also gives insight into the physical aspects of cavitation bubble dynamics near the air-liquid interface on the microscale.

Effects of Sodium Dodecyl Sulfate on a Single Cavitation Bubble**Supported by the National Natural Science Foundation of China under Grant Nos 11334005 and 11574150.

Dynamics of a single cavitation bubble in sodium dodecyl sulfate (SDS) aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging technique, and the ambient radius is obtained by fitting the numerical calculation based on the Rayleigh–Plesset bubble dynamics model to the experimental data. The results show that, under the same driving condition, the ambient radius of the cavitation bubble decreases correspondingly with the increase of SDS concentration within the critical micelle concentration, while the compression ratio of the radius increases, which indicates that the addition of SDS decreases the internal molecular number of the cavitation bubble and increases the power capability of the cavitation bubble. In addition, bubble oscillation increases the concentration of the surfactant molecules on the bubble wall, so that the effect of SDS on a single cavitation bubble is reduced when the SDS concentration is greater than 0.8 mM.

How important is the liquid bulk viscosity effect on the dynamics of a single cavitation bubble?

The influence of liquid bulk viscosity on the dynamics of a single cavitation bubble is numerically studied via Gilmore model with a new modified boundary condition at bubble interface. In order to more accurately describe the interior gas thermodynamics, a hydrochemical model is used. The numerical results for an argon bubble in water and aqueous H2SO4 show that including the liquid bulk viscosity slightly affects the bubble dynamics in collapse phase. This effect becomes significant only at high ultrasonic amplitudes and high viscosities. Moreover, the maximum pressure value inside the bubble is much more influenced than the maximum temperature. This finding lends support to results of Shen et al. [25] and significantly differ from some previous results reported in the literature.

Mechanistic investigations in sonochemical degradation of trihalomethanes in presence of non–porous and mesoporous silica nanospheres

This study reports mechanistic investigations in sonochemical degradation of four Trihalomethanes (THMs), viz. CHCl3, CHCl2Br, CHClBr2 and CHBr3, in presence of non–porous and mesoporous silica nanospheres. Degradation reactions of THMs were carried out under identical conditions with addition of silica nanospheres. Concurrently, simulations of cavitation bubble dynamics were carried out. Mesoporous silica nanospheres with the largest surface area and the highest mean pore diameter yielded the highest enhancement in degradation of the THMs. These results were also corroborated by H2O2 dosimetry. The concentration profiles of the THMs were fitted to pseudo 1st order kinetic model. Although mean pore sizes of mesoporous silica nanospheres were smaller than minimum threshold radius for transient cavitation, these nanospheres provided surface-induced and pore-induced nucleation to augment cavitation bubble population in medium. The highest nanosphere–induced enhancement in degradation was obtained for CHBr3, while the highest total degradation was obtained for CHCl3. With concurrent analysis of experimental and simulations results, an attempt is made to deduce the predominant physical mechanism of degradation of the THMs.

Cavitation Bubble Dynamics Induced by Hydrodynamic Pressure Oil Film in Ultrasonic Vibration Honing

During ultrasonic vibration honing (UVH), a thin hydrodynamic oil film formed can seriously affect the cavitation effect in the grinding fluid, but the mechanism is still unclear now. Based on the hydrodynamics theory, a revised cavitation bubble model with oil film pressure is developed, and it has been calculated by the four-order Runge–Kutta method. The calculation results show that the oil film pressure under UVH is a positive–negative alternant pulse pressure, and it can induce the secondary expansion of the bubble, leading to double microjets during the process of the bubble collapsing. The effects of ultrasonic amplitude, ultrasonic frequency, oil film height, and reciprocation speed of the honing stone on the bubble dynamics are discussed. With the increase of ultrasonic amplitude, the amplitude of the bubble expansion is increased, and the oscillation interval is extended. As increasing normalized oil film height, the variation of the bubble first expansion is slight, while the amplitude of the bubble secondary expansion is reduced and the oscillation interval is also shortened. The main effect of ultrasonic frequency and reciprocation speed of the honing stone on the bubble dynamics is connected with the secondary bubble expansion. The bubble secondary expansion is decreased with the increasing reciprocation speed of the honing stone, ultrasonic frequency, and oil film height. The results of the simulations are consistent with the surface roughness measurements well, which provides a theoretical prediction method of cavitation bubbles control.

Dynamics of laser-induced cavitation bubbles near two perpendicular rigid walls

The behaviour of a laser-induced cavitation bubble near two perpendicular rigid walls and its dependence on the distance between bubble and walls is investigated experimentally. It was shown by means of high-speed photography with $100\,000~\text{frames}~\text{s}^{-1}$ that an inclined jet is formed during bubble collapse and the bubble migrates in the direction of the jet. At a given position of the bubble with respect to the horizontal wall, the inclination of the jet increases with decreasing distance between the bubble and the second, vertical wall. A bubble generated at equal distances from the walls develops a jet that is directed in their bisection. The penetration of the jet into the opposite bubble surface leads to the formation of an asymmetric toroidal bubble that is perpendicular to the jet direction. At a large distance from the rigid walls, the toroidal bubble collapses in the radial direction, eventually disintegrating into tiny microbubbles. When the bubble is in contact with the horizontal wall at its maximum expansion, the toroidal ring collapses in both radial and toroidal directions, starting from the bubble part opposite to the vertical wall, and the bubble achieves a crescent shape at the moment of second collapse. The bubble oscillation is accompanied by a strong migration along the horizontal wall.

Mechanistic investigations in ultrasonic pretreatment and anaerobic digestion of landfill leachates

This study has attempted to gain mechanistic insight into ultrasound assisted pretreatment of landfill leachate (prior to anaerobic digestion) by coupling experimental results with simulations of cavitation bubble dynamics. Essentially, individual roles of physical and chemical effects induced by sonication in the process have been identified. Changes in properties of leachate (such as sCOD, tCOD, NH3-N and acetate concentrations) subjected to sonication at different power levels have been studied. Sonication generated intense microconvection in system that caused faster disintegration and solubilization of biosolids. However, for high power input, where transient cavitation occurred in solution, degradation of organic matter by oxidizing radicals generated by cavitation bubbles occurred that reduced sCOD value resulting in low biogas yield in anaerobic digestion. Sonication at low to moderate power input, where stable cavitation prevailed, caused disintegration and solubilization, but not degradation, of biosolids resulting in higher sCOD value and biogas yield.

Inertial Microcavitation as a Neural Cell Damage Mechanism in a 3D In Vitro Model of Blast Traumatic Brain Injury

Blast traumatic brain injury (bTBI) is a leading cause of injury in the armed forces. Diffuse axonal injury, the hallmark feature of blunt TBI, has been investigated in direct mechanical loading conditions. However, recent evidence suggests inertial cavitation as a possible bTBI mechanism. Cavitation occurs via a low-pressure region caused by pressure waves, and is strongly dependent on local geometric and mechanical properties. The structural damage features as the result of cavitation - particularly at the cellular level - are incompletely understood. Microcavitation is induced via single, high-energy laser pulses, wherein single bubbles are generated within the focal plane of the sample, recorded at high-speed and analyzed with custom image processing algorithms. Initial work characterized distinct strain regimes where different modalities of cellular injury dominated, including complete cellular fragmentation, severe somatic and projection fragmentation, limited somatic damage with severe projection fragmentation, and limited projection damage. Preliminary actin fragmentation results indicated the presence of severe cytoskeletal disruptions up to the fragmentation radius dictated by cavitation bubble dynamics. The focus of this study is the examination of cytoskeletal disruption, including microtubule disruption and actin fragmentation. In addition, cellular viability and cellular apoptotic pathway studies are examined within the context of the larger pathology of bTBI.