Cavitation Bubbles In Water Research Articles

High-speed film-thickness measurements between a collapsing cavitation bubble and a solid surface with total internal reflection shadowmetry

The time evolution of the liquid-film thickness of a single cavitation bubble in water collapsing onto a solid surface is measured. To this end, total internal reflection (TIR) shadowmetry is developed, a technique based on TIR and the imaging of shadows of an optical structure on a polished glass surface. The measurements are performed at frame rates up to 480 kHz. Simultaneous high-speed imaging of the bubble shape at up to 89 kHz allows relating the evolution of the film thickness to the bubble dynamics. With a typical maximum bubble radius of 410 µm, we varied the nondimensional stand-off distance γ from 0.47 to 1.07. We find that during the first collapse phase, the bubble does not come in direct contact with the solid surface. Instead, when the bubble collapses, the jet impacts on a liquid film that always resides between the bubble and solid. At jet impact, it is 5–40 µm thick, depending on γ. Also, during rebound, at any given point in time, most or all of the then overall toroidal bubble is not in contact with the solid surface.

Strong compression of bubbles in water, acetone and benzol

Strong compression of the medium in cavitation bubbles in water, acetone and benzol realizing in the final stage of their collapse in the initially motionless liquid at a temperature of 293 K is considered. At the beginning of the collapse, the radius of the bubbles is 500 μm, the vapor in the bubbles is in its saturation state at the temperature of the surrounding liquid. The pressure of water and benzol is varied in the range 1 ≤ p0 ≤ 100 bar to determine its values at which the degree of compression of the medium inside the cavitation bubbles in these liquids is close to that achieved inside the cavitation bubble in acetone at the pressure p0 = 15 bar. It is shown that in the case of the bubble in benzol such a degree of the vapor compression can be achieved at p0 = 4 bar, whereas in the case of the bubble in water, even p0 = 100 bar is not enough.

Effect of entropy on the nucleation of cavitation bubbles in water under tension.

Water can exist in a metastable liquid state under tension for long times before the system relaxes into the vapor via cavitation, i.e., bubble nucleation. Microscopic information on the cavitation process can be extracted from experimental data by the use of the nucleation theorem, which relates measured cavitation rates to the size of the critical bubble. To apply the nucleation theorem to experiments performed along an isochoric path, for instance, in cavitation experiments in mineral inclusions, knowledge of the bubble entropy is required. Using computer simulations, we compute the entropy of bubbles in water as a function of their volume over a wide range of tensions from free energy calculations. We find that the bubble entropy is an important contribution to the free energy that significantly lowers the barrier to bubble nucleation, thereby facilitating cavitation. Furthermore, the bubble entropy per surface area depends on the curvature of the liquid-vapor interface, decreasing approximately linearly with its mean curvature over the studied range of bubble volumes. At room temperature, the entropy of a flat liquid-vapor interface at ambient pressure is very similar to that of critical bubbles over a wide range of tensions, which justifies the use of the former as an approximation when interpreting data from experiments. Based on our simulation results, we obtain an estimate for the volume of the critical bubble from experimentally measured cavitation rates.

Application of analyzer based X-ray imaging technique for detection of ultrasound induced cavitation bubbles from a physical therapy unit.

BackgroundThe observation of ultrasound generated cavitation bubbles deep in tissue is very difficult. The development of an imaging method capable of investigating cavitation bubbles in tissue would improve the efficiency and application of ultrasound in the clinic. Among the previous imaging modalities capable of detecting cavitation bubbles in vivo, the acoustic detection technique has the positive aspect of in vivo application. However the size of the initial cavitation bubble and the amplitude of the ultrasound that produced the cavitation bubbles, affect the timing and amplitude of the cavitation bubbles’ emissions.MethodsThe spatial distribution of cavitation bubbles, driven by 0.8835 MHz therapeutic ultrasound system at output power of 14 Watt, was studied in water using a synchrotron X-ray imaging technique, Analyzer Based Imaging (ABI). The cavitation bubble distribution was investigated by repeated application of the ultrasound and imaging the water tank. The spatial frequency of the cavitation bubble pattern was evaluated by Fourier analysis. Acoustic cavitation was imaged at four different locations through the acoustic beam in water at a fixed power level. The pattern of cavitation bubbles in water was detected by synchrotron X-ray ABI.ResultsThe spatial distribution of cavitation bubbles driven by the therapeutic ultrasound system was observed using ABI X-ray imaging technique. It was observed that the cavitation bubbles appeared in a periodic pattern. The calculated distance between intervals revealed that the distance of frequent cavitation lines (intervals) is one-half of the acoustic wave length consistent with standing waves.ConclusionThis set of experiments demonstrates the utility of synchrotron ABI for visualizing cavitation bubbles formed in water by clinical ultrasound systems working at high frequency and output powers as low as a therapeutic system.

J0540303 キャビテーション気泡の生成に関する分子動力学的研究

Nucleation and growth processes of cavitation bubble in water are simulated by molecular dynamics (MD) method. The water molecule is approximated by a particle with Lennard-Jones potential. The simulated model consists of a cube shaped decompression MD cell under periodic boundary condition. The gas and liquid phases are defined by number density. The growth process of cavitation babbles is visualized by the number density as a continuous quantity which is converted from the molecular configuration as a discrete quantity.

Multiscale model of cavitation bubble formation and breakdown

Cavitation damage is responsible for initial pitting of kidney stone surfaces, damage that is thought to play an important role in shock wave lithotripsy. We introduce a multiscale model of the formation of cavitation bubbles in water, and subsequent breakdown. At a macroscopic, continuum scale cavitation is modeled by the 3D Euler equations with a Tait equation of state. Adaptive mesh refinement is used to provide increased resolution at the liquid/vapor boundary. Cells with both liquid and vapor phases are flagged by the continuum solver for mesoscale, kinetic modeling by a lattice Boltzmann description capable of capturing non-equilibrium behavior (e.g., phase change, energetic jet impingement). Isolated and interacting two-bubble configurations are studied. Computational simulation results are compared with high-speed experimental imaging of individual bubble dynamics and bubble–bubble interaction. The model is used to build a statistical description of multiple-bubble interaction, with input from cavitation cloud imaging. [Work supported by NIH through 5R37DK052985-18.]

HIGH RESOLUTION OPTICAL EXPERIMENTAL TECHNIQUE FOR COMPUTING PULSED LASER-INDUCED CAVITATION BUBBLE DYNAMICS IN A SINGLE SHOT

The experiments conducted in this study consisted of a series of plasma generated cavitation bubbles in water, obtained by focusing a 532-nm Q-switched Nd:YAG nanosecond-pulsed laser. For the purpose of detection of such cavitation bubbles, a novel direct light transmission technique is used, referred to as spatial transmission modulation (STM), consisting of a nearly collimated beam of light passing through the sample at the point where the cavitation bubble is formed. The presence of the cavitation bubble modifies the direct light transmission, which is detected with a photodiode located at the opposite end. This is observed as an electrical signal response with an oscilloscope. A 1-megapixel high-speed video camera simultaneously records the cavitation event. The video was taken in an orthogonal direction with respect to the STM optical axis and was triggered simultaneously with an oscilloscope using the electronic synchronization signal from the pulsed laser. Data from the highspeed video was used to show that a computational spatial energetic analysis from the continuous laser probe beam is a valid method to directly obtain the cavitation bubble evolution from a single shot pulse. © 2013 by Begell House, Inc.

Finite volume simulation of unsteady shock‐cavitation in compressible water

SUMMARYThe present paper extends an established Riemann‐based finite volume hydrocode for compressible pure water to admit change of phase. The thermal and caloric behaviour of water and water vapour is described by a one‐fluid model on the assumption that the two‐phase regime can be described locally within a finite volume cell as a homogeneous mixture that remains in thermodynamic equilibrium. Closure of the equation set is achieved by deriving equations of state for pure fluids and the mixture that cover all possible fluid states. Following a description of the flow model and the numerical method, computations are carried out to demonstrate the potential of the method. Calculations include a one‐dimensional cavitation tube, one‐dimensional condensation front, collapse of a cavitation bubble in water in one dimension, and an unsteady two‐dimensional hypervelocity flow past a cavitating hydrofoil. Copyright © 2012 John Wiley & Sons, Ltd.

Laser Peening Induced Shock Waves and Cavitation Bubbles in Water Studied by Optical Schlieren Visualization

A temporal and spatial study of the dynamics of generated shock waves and cavitation bubbles in water by laser peening using nanosecond Nd:YAG laser pulses is reported. False schlieren photographs of the zone surrounding the laser spot on the target were recorded by a fast ICCD camera. The developed experimental setup allowed us to obtain a visualization of the different phenomena (hemispherical, cylindrical and plane shock fronts, cavitation bubbles, phase disturbance tracks, plasma formation, etc.) that occur after the arrival of the laser pulse and that contain valuable information about the mechanical processes that take place on the sample.

Oscillation characteristics of a laser-induced cavitation bubble in water at different temperatures

Comprehensive numerical and experimental analyses of the effect of temperature on cavitation oscillations are performed. In the experimental study, the oscillation of a laser-generated single cavitation bubble near a rigid boundary is obtained using a fiber-optic diagnostic technique based on optical beam detection (OBD). The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. And cavitation bubble tests are performed using water at different temperatures, and its temperature ranges from freezing point (0 °C) to near boiling. Furthermore, a modified Rayleigh–Plesset equation is derived for calculating the temporal development of the bubble radius at different temperatures. Both the experimental and the numerical results show that the maximum bubble radius and bubble lifetime both increase as temperature increases. The mechanism behind it has also been discussed.

The influence of thermodynamic gas parameters on laser-induced bubble dynamics in water

The oscillating properties of laser-induced cavitation bubbles in water are investigated by means of a fiber-optic sensor based on optical beam deflection. The experimental results show two important points. One is that the smaller the bubble radius the more quickly the bubble surface moves. Thus, the variations of the temperature and the pressure inside the bubble will be close to those of an adiabatic process. The other is that the high-energy vapor inside the newborn bubble diffuses and coagulates rapidly through violent expansion and thermal conduction. Thus, the gas content of the bubble reduces significantly in the first oscillation. Numerical simulation is made for the bubble model with consideration of liquid viscosity, surface tension, and gas content. Through modification of the polytropic index and the gas content parameter, two parameters of this model, the numerical results fit the experimental results well.

New evidence for the inverse dependence of mechanical and chemical effects on the frequency of ultrasound

Acoustic cavitation has been the subject of research and discussion for many years and it is the underlying driving force for sonochemistry. The collapse of acoustic cavitation bubbles in water near to a surface can bring about significant surface modification in terms of the mechanical damage caused by the asymmetric collapse of the bubbles which cause erosion and abrasion. A second effect of acoustic cavitation is the formation of short lived radicals caused by the breakdown of water inside the bubble. For the first time the dependence of these effects has been observed on the surface of a plastic material as a function of ultrasonic frequency.

Interaction dynamics of spatially separated cavitation bubbles in water

We present a high-speed photographic analysis of the interaction of cavitation bubbles generated in two spatially separated regions by femtosecond laser-induced optical breakdown in water. Depending on the relative energies of the femtosecond laser pulses and their spatial separation, different kinds of interactions, such as a flattening and deformation of the bubbles, asymmetric water flows, and jet formation were observed. The results presented have a strong impact on understanding and optimizing the cutting effect of modern femtosecond lasers with high repetition rates (>1 MHz).

Particle tracking velocimetry of the flow field around a collapsing cavitation bubble

The velocity field in the vicinity of a laser-generated cavitation bubble in water is investigated by means of particle tracking velocimetry (PTV). Two situations are explored: a bubble collapsing spherically and a bubble collapsing aspherically near a rigid wall. In the first case, the accuracy of the PTV method is assessed by comparing the experimental data with the flow field around the bubble as obtained from numerical simulations of the radial bubble dynamics. The numerical results are matched to the experimental radius–time curve extracted from high-speed photographs by tuning the model parameters. Trajectories of tracer particles are calculated and used to model the experimental process of the PTV measurement. For the second case of a bubble collapsing near a rigid wall, both the bubble shape and the velocity distribution in the fluid around the bubble are measured for different standoff parameters γ at several instants in time. The results for γ > 1 are compared with the corresponding results of a boundary-integral simulation. For both cases, good agreement between simulation and experiment is found.

Quantitative ultrasound method to detect and monitor laser-induced cavitation bubbles

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble's origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications.

Thermodynamic and kinetic considerations of nucleation and stabilization of acoustic cavitation bubbles in water

Qualitative explanation for a homogeneous nucleation of acoustic cavitation bubbles in the incompressible liquid water with simple phenomenological approach has been provided via the concept of the desorbtion of the dissolved gas and the vaporization of local liquid molecules. The liquid medium has been viewed as an ensemble of lattice structures. Validity of the lattice structure approach against the Brownian motion of molecules in the liquid state has been discussed. Criterion based on probability for nucleus formation has been defined for the vaporization of local liquid molecules. Energy need for the enthalpy of vaporization has been considered as an energy criterion for the formation of a vaporous nucleus. Sound energy, thermal energy of the liquid bulk (Joule–Thomson effect) and free energy of activation, which is associated with water molecules in the liquid state (Brownian motion) as per the modified Eyring’s kinetic theory of liquid are considered as possible sources for the enthalpy of vaporization of water molecules forming a single unit lattice. The classical nucleation theory has then been considered for expressing further growth of the vaporous nucleus against the surface energy barrier. Effect of liquid property (temperature), and effect of an acoustic parameter (frequency) on an acoustic cavitation threshold pressure have been discussed. Kinetics of nucleation has been considered.

Luminescence from transient cavitation bubbles in water

Large size single transient cavitation bubbles of maximum diameters up to 2.6 cm have been generated in water by the “tube arrest” method. The light emissions with light pulses width less than 750 ps during the collapse of the bubbles would be the multibubble sonoluminescence as shown by the analyses of high-speed photograph and light emission data.

Luminescence of transient bubbles at elevated ambient pressures.

The light emission of transient laser-produced cavitation bubbles in water is investigated in a range of ambient pressures up to 5 bar and laser energies up to 30 mJ. At elevated pressures bubble luminescence can be increased more than two fold for bubbles created with the same laser energy, and up to almost an order of magnitude comparing bubbles of the same maximum radius. Both the conversion of large laser energies into mechanical energy of the bubble, and the conversion of mechanical energy into light are improved at higher pressure.

Zur Entstehung von Kavitationsblasen bei der Erbium:YAG-Laser-Vitrektomie

Clinical and experimental studies demonstrated the potential advantages of Erbium:YAG laser vitrectomy for posterior segment surgery. However, a detailed knowledge on the laser-tissue interaction is needed for an optimization of new ophthalmic applications. The aim of this experimental work was to investigate the cavitation bubble formation during Erbium:YAG laser vitrectomy and to find optimized laser parameters and the best geometry of the aspiration port of the microsurgical probe. We investigated the formation of cavitation bubbles in water by high-speed photography. The output energy at the quartz tip reached up to 50 mJ and the laser pulse duration ranged from 50 to 300 microseconds. Various commercially available microsurgery probes were investigated regarding the extent of the cavitation bubbles. The threshold for laser-induced cavitation bubble formation was found to be 0.32 +/- 0.1 mJ for a laser pulse duration of 130 microseconds and a core diameter of 320 microns of the quartz fiber tip. The length of the cavitation bubbles increases with the laser pulse energy up to a length of 1.6 mm at a pulse energy of 10 mJ. In contrast, the size of the vapor bubbles decreases with an increase of the laser pulse duration. A slit-shaped aspiration port led to a 50% smaller volume of the cavitation bubble exiting the port compared with a circular aspiration port. The optimized laser parameters and microsurgery probe geometry may significantly decrease the risk of intraoperative ocular damages during Erbium:YAG laser vitrectomy.

Influence of shock wave pressure amplitude and pulse repetition frequency on the lifespan, size and number of transient cavities in the field of an electromagnetic lithotripter

Monitoring the generation of cavitation is of great interest for diagnostic and therapeutic use of ultrasound in medicine, since cavitation is considered to play a major role in nonthermal ultrasound interactions with tissue. Important parameters are the number of cavitation events and the energy released during the bubble collapse. This energy is correlated to the maximum bubble radius which is related to the cavitation lifespan. The aim of this study was therefore to investigate the influence of the acoustic pressure amplitude and the pulse repetition frequency (PRF) in the field of a lithotripter (Lithostar, Siemens) on the number, size and lifespan of transient cavitation bubbles in water. We used scattered laser light recorded by a photodiode and stroboscopic photographs to monitor the cavitation activity. We found that PRF (range 0.5-5 Hz) had no influence on the cavitation bubble lifespan and size, whereas lifespan and size increased with the acoustic pressure amplitude. In contrast, the number of cavitation events strongly increased with PRF, whereas the pressure amplitude had no significant influence on the number of cavitation events. Thus, by varying the pressure amplitude and PRF, it might be possible to deliver a defined relative number of cavitations at a defined relative energy level in a defined volume. This seems to be relevant to further studies that address the biological effects of transient cavitation occurring in the fields of lithotripters.