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1

Birth and growth of cavitation bubbles within water under tension  

E-print Network

Water under tension, such as the water rising in tree vessels, is in a metastable state. Water cavitates spontaneously when the tension is high enough, as observed at equilibrium in the water filled holes of a drying hydrogel, called artifical trees. Here, in order to understand the dynamics of cavitation in tensed water, we directly trigger cavitation events, taking advantage of the disturbance generated by a focused laser pulse. We find that the inception of a bubble progresses in two stages. The first stage is ultra-fast, lasting less than microseconds, during which a bubble with a finite volume suddenly appears. This event relaxes the water tension, that we can therefore estimate. A second, slower stage follows when water diffuses into the surrounding medium.

Vincent, Olivier; Quinto-Su, Pedro A; Ohl, Claus-Dieter

2011-01-01

2

Simulation of heat transfer with the growth and collapse of a cavitation bubble near the heated wall  

NASA Astrophysics Data System (ADS)

The growth and collapse behaviors of a single cavitation bubble near a heated wall and its effect on the heat transfer are numerically investigated. The present study is designed to reveal the mechanism of cavitation enhanced heat transfer from a microscopic perspective. In the simulation, the time-dependent Navier-Stokes equations are solved in an axisymmetric two-dimensional domain. The volume of fluid (VOF) method is employed to track the liquid-gas interface. It is assumed that the gas inside the bubble is compressible vapor, and the surrounding liquid is incompressible water. Mass transfer between two phases is ignored. The calculated bubble profiles were compared to the available experimental data, and a good agreement was obtained. Then, the relationship among bubble motion, flow field and surface heat transfer coefficient was analyzed. On this basis, the effects of such factors as the initial distance between the bubble and the wall, the initial vapor pressure and the initial bubble nucleus size on the heat transfer enhancement are discussed. The present study is helpful to understand the heat transfer phenomenon in presence of cavitation bubble in liquid.

Liu, Bin; Cai, Jun; Li, Fengchao; Huai, Xiulan

2013-08-01

3

Interaction mechanism of double bubbles in hydrodynamic cavitation  

NASA Astrophysics Data System (ADS)

Bubble-bubble interaction is an important factor in cavitation bubble dynamics. In this paper, the dynamic behaviors of double cavitation bubbles driven by varying pressure field downstream of an orifice plate in hydrodynamic cavitation reactor are examined. The bubble-bubble interaction between two bubbles with different radii is considered. We have shown the different dynamic behaviors between double cavitation bubbles and a single bubble by solving two coupling nonlinear equations using the Runge-Kutta fourth order method with adaptive step size control. The simulation results indicate that, when considering the role of the neighbor smaller bubble, the oscillation of the bigger bubble gradually exhibits a lag in comparison with the single-bubble case, and the extent of the lag becomes much more obvious as time goes by. This phenomenon is more easily observed with the increase of the initial radius of the smaller bubble. In comparison with the single-bubble case, the oscillation of the bigger bubble is enhanced by the neighbor smaller bubble. Especially, the pressure pulse of the bigger bubble rises intensely when the sizes of two bubbles approach, and a series of peak values for different initial radii are acquired when the initial radius ratio of two bubbles is in the range of 0.9˜1.0. Although the increase of the center distance between two bubbles can weaken the mutual interaction, it has no significant influence on the enhancement trend. On the one hand, the interaction between two bubbles with different radii can suppress the growth of the smaller bubble; on the other hand, it also can enhance the growth of the bigger one at the same time. The significant enhancement effect due to the interaction of multi-bubbles should be paid more attention because it can be used to reinforce the cavitation intensity for various potential applications in future.

Li, Fengchao; Cai, Jun; Huai, Xiulan; Liu, Bin

2013-06-01

4

Level set method for numerical simulation of a cavitation bubble, its growth, collapse and rebound near a rigid wall  

NASA Astrophysics Data System (ADS)

A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier Stokes equation in the liquid region is solved by MAC projection algorithm combined with second-order ENO scheme for the advection terms. The moving interface is captured by the level set function, and the interface velocity is resolved by “one-side” velocity extension from the liquid region to the bubble region, complementing the second-order weighted least squares method across the interface and projection inside bubble. The use of non-uniform grid overcomes the difficulty caused by the large computational domain and very small bubble size. The computation is very stable without suffering from large flow-field gradients, and the results are in good agreements with other studies. The bubble interface kinematics, dynamics and its effect on the wall are highlighted, which shows that the code can effectively capture the “shock wave”-like pressure and velocity at jet impact, toroidal bubble, and complicated pressure structure with peak, plateau and valley in the later stage of bubble oscillating.

Huang, Juntao; Zhang, Huisheng

2007-12-01

5

Sonoporation from jetting cavitation bubbles.  

PubMed

The fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads to the detachment of cells. Cells at the edge of the circular area of detachment are found to be permanently porated, whereas cells at some distance from the detachment area undergo viable cell membrane poration (sonoporation). The wall flow field leading to cell detachment is modeled with a self-similar solution for a wall jet, together with a kinetic ansatz of adhesive bond rupture. The self-similar solution for the delta-type wall jet compares very well with the full solution of the Navier-Stokes equation for a jet of finite thickness. Apart from annular sites of sonoporation we also find more homogenous patterns of molecule delivery with no cell detachment. PMID:16950843

Ohl, Claus-Dieter; Arora, Manish; Ikink, Roy; de Jong, Nico; Versluis, Michel; Delius, Michael; Lohse, Detlef

2006-12-01

6

Sonoluminescence, sonochemistry and bubble dynamics of single bubble cavitation  

NASA Astrophysics Data System (ADS)

The amount of hydroxyl radicals produced from a single cavitation bubble was quantified by terephthalate dosimetry at various frequencies and pressure amplitudes, while the dynamics of the single bubble was observed by stroboscopic and light-scattering methods. Also, sonoluminescence (SL), sonochemiluminescence (SCL) of luminol, and sodium atom emission (Na*) in the cavitation field were observed. The amount of hydroxyl radicals per cycle as well as the intensity of SL was proportional to pressure amplitude at every frequency performed, and it decreased with increasing frequency. When the single bubble was dancing with a decrease in pressure amplitude, however, the amount of hydroxyl radicals was greater than that for the stable bubble at the higher pressure amplitude and did not significantly decrease with frequency. Furthermore, SCL and Na* were detected only under unstable bubble conditions. These results imply that the instability of bubbles significantly enhances sonochemical efficiency for non-volatile substances in liquid phase.

Hatanaka, Shin-ichi

2012-09-01

7

Bubble proliferation in the cavitation field of a shock wave lithotripter  

PubMed Central

Lithotripter shock waves (SWs) generated in non-degassed water at 0.5 and 2 Hz pulse repetition frequency (PRF) were characterized using a fiber-optic hydrophone. High-speed imaging captured the inertial growth-collapse-rebound cycle of cavitation bubbles, and continuous recording with a 60 fps camcorder was used to track bubble proliferation over successive SWs. Microbubbles that seeded the generation of bubble clouds formed by the breakup of cavitation jets and by bubble collapse following rebound. Microbubbles that persisted long enough served as cavitation nuclei for subsequent SWs, as such bubble clouds were enhanced at fast PRF. Visual tracking suggests that bubble clouds can originate from single bubbles. PMID:21877776

Pishchalnikov, Yuri A.; Williams, James C.; McAteer, James A.

2011-01-01

8

Cavitation Bubble Cluster Activity in the Breakage of Kidney Stones by Lithotripter Shock Waves  

PubMed Central

High-speed photography was used to analyze cavitation bubble activity at the surface of artificial and natural kidney stones during exposure to lithotripter shock waves in vitro. Numerous individual bubbles formed at the surface of stones, but these bubbles did not remain independent and combined with one another to form bubble clusters. Bubble clusters formed at the proximal end, the distal end, and at the sides of stones. Each cluster collapsed to a narrow point of impact. Collapse of the proximal cluster caused erosion at the leading face of the stone and the collapse of clusters at the sides of stones appeared to contribute to the growth of cracks. Collapse of the distal cluster caused minimal damage. We conclude that cavitation-mediated damage to stones was due not to the action of solitary bubbles, but to the growth and collapse of bubble clusters. PMID:14565872

Pishchalnikov, Yuriy A.; Sapozhnikov, Oleg A.; Bailey, Michael R.; Williams, James C.; Cleveland, Robin O.; Colonius, Tim; Crum, Lawrence A.; Evan, Andrew P.; McAteer, James A.

2008-01-01

9

Cavitation Bubble Nucleation by Energetic Particles  

SciTech Connect

In the early sixties, experimental measurements using a bubble chamber confirmed quantitatively the thermal spike theory of bubble nucleation by energetic particles: the energy of the slow, heavy alpha decay recoils used in those experiments matched the calculated bubble nucleation energy to within a few percent. It was a triumph, but was soon to be followed by a puzzle. Within a couple of years, experiments on similar liquids, but well below their normal boiling points, placed under tensile stress showed that the calculated bubble nucleation energy was an order of magnitude less than the recoil energy. Why should the theory work so well in the one case and so badly in the other? How did the liquid, or the recoil particle, "know" the difference between the two experiments? Another mathematical model of the same physical process, introduced in 1967, showed qualitatively why different analyses would be needed for liquids with high and low vapor pressures under positive or negative pressures. But, the quantitative agreement between the calculated nucleation energy and the recoil energy was still poor--the former being smaller by a factor of two to three. In this report, the 1967 analysis is extended and refined: the qualitative understanding of the difference between positive and negative pressure nucleation, "boiling" and "cavitation" respectively, is retained, and agreement between the negative pressure calculated to be needed for nucleation and the energy calculated to be available is much improved. A plot of the calculated negative pressure needed to induce bubble formation against the measured value now has a slope of 1.0, although there is still considerable scatter in the individual points.

West, C.D.

1998-12-01

10

Prediction of Cavitation Intensity and Erosion Area in Centrifugal Pump by Using Cavitating Flow Simulation with Bubble Flow Model  

NASA Astrophysics Data System (ADS)

We developed a numerical simulation code and a method of estimation for predicting the cavitation erosion in pumps. Cavitation erosion is closely related to cavitation intensity based on bubble dynamics. A “bubble flow model” simulates detailed bubble behavior in a cavitating flow. Cavitation intensity was estimated by analyzing the bubble pressure and bubble nuclei distribution in a centrifugal pump. We simulated the impulsive bubble pressure that varied in microseconds. The impulsive pressure was considered to be related to actual bubble collapse, which caused cavitation erosion. The erosion area was experimentally detected using a paint method. The predicted high cavitation intensity area agreed well with the experimental erosion area, since the predicted and experimental areas were both located between the shroud and mid-point of the blade near the leading edge. Our code was thus effective for estimating the cavitation intensity and predicting the erosion area around the impeller of a centrifugal pump.

Fukaya, Masashi; Tamura, Yoshiaki; Matsumoto, Yoichiro

11

Cavitation bubble dynamics inside liquid drops in microgravity.  

PubMed

We studied spark-generated cavitation bubbles inside water drops produced in microgravity. High-speed visualizations disclosed unique effects of the spherical and nearly isolated liquid volume. In particular, (1) toroidally collapsing bubbles generate two liquid jets escaping from the drop, and the "splash jet" discloses a remarkable broadening. (2) Shock waves induce a strong form of secondary cavitation due to the particular shock wave confinement. This feature offers a novel way to estimate integral shock wave energies in isolated volumes. (3) Bubble lifetimes in drops are shorter than in extended volumes in remarkable agreement with herein derived corrective terms for the Rayleigh-Plesset equation. PMID:17026369

Obreschkow, D; Kobel, P; Dorsaz, N; de Bosset, A; Nicollier, C; Farhat, M

2006-09-01

12

Cavitation Bubble Dynamics in Liquids of Different Viscosity  

Microsoft Academic Search

A single bubble in liquids is produced by using a high-intensity laser pulse and the dynamic characteristics of the oscillating bubble in glycerin-water mixtures with different viscosity are investigated by a sensitive fiber-optic sensors based on optical beam deflection (OBD). By analyzing the characteristic signals, the bubble radii and the oscillation times are determined. The experimental results show that Cavitation

Xiu-Mei Liu; Xin-Hua Liu; Jie He; You-Fu Hou; Jian Lu; Xiao-Wu Ni

2010-01-01

13

Comparison of numerical simulations and laboratory studies of shock waves and cavitation bubble growth produced by optical breakdown in water  

SciTech Connect

In numerical calculations of idealized bubble dynamics test problems, Los Alamos computational tools perform well. A realistic equation of state must be used and geometrical features must be carefully modeled to simulate experiments accurately. In this work, we compare numerical simulations taking these features into account with experiments performed at the Medizinisches Laserzentrum Lubeck. We compare the measured and calculated positions of the shock front and of the bubble wall as a function of time in the laser optical breakdown of water produced by 30-ps 1-mJ Nd:YAG laser pulses.

Chapyak, E.J.; Godwin, R.P. [Los Alamos National Lab., NM (United States); Vogel, A. [Medizinisches Laserzentrum Luebeck GmbH (Germany)

1997-04-01

14

Controlled permeation of cell membrane by single bubble acoustic cavitation  

PubMed Central

Sonoporation is the membrane disruption generated by ultrasound and has been exploited as a non-viral strategy for drug and gene delivery. Acoustic cavitation of microbubbles has been recognized to play an important role in sonoporation. However, due to the lack of adequate techniques for precise control of cavitation activities and real-time assessment of the resulting sub-micron process of sonoporation, limited knowledge has been available regarding the detail processes and correlation of cavitation with membrane disruption at the single cell level. In the current study, we developed a combined approach including optical, acoustic, and electrophysiological techniques to enable synchronized manipulation, imaging, and measurement of cavitation of single bubbles and the resulting cell membrane disruption in real-time. Using a self-focused femtosecond laser and high frequency (7.44 MHz) pulses, a single microbubble was generated and positioned at a desired distance from the membrane of a Xenopus oocyte. Cavitation of the bubble was achieved by applying a low frequency (1.5 MHz) ultrasound pulse (duration 13.3 or 40 µs) to induce bubble collapse. Disruption of the cell membrane was assessed by the increase in the transmembrane current (TMC) of the cell under voltage clamp. Simultaneous high-speed bright field imaging of cavitation and measurements of the TMC were obtained to correlate the ultrasound-generated bubble activities with the cell membrane poration. The change in membrane permeability was directly associated with the formation of a sub-micrometer pore from a local membrane rupture generated by bubble collapse or bubble compression depending on ultrasound amplitude and duration. The impact of the bubble collapse on membrane permeation decreased rapidly with increasing distance (D) between the bubble (diameter d) and the cell membrane. The effective range of cavitation impact on membrane poration was determined to be D/d = 0.75. The maximum mean radius of the pores was estimated from the measured TMC to be 0.106 ± 0.032 µm (n = 70) for acoustic pressure of 1.5 MPa (duration 13.3 µs), and increased to 0.171 ± 0.030 µm (n = 125) for acoustic pressure of 1.7 MPa and to 0.182 ± 0.052 µm (n=112) for a pulse duration of 40 µs (1.5 MPa). These results from controlled cell membrane permeation by cavitation of single bubbles revealed insights and key factors affecting sonoporation at the single cell level. PMID:21945682

Zhou, Y.; Yang, K.; Cui, J.; Ye, J. Y.; Deng, C. X.

2011-01-01

15

On acoustic cavitation of slightly subcritical bubbles Anthony Harkin  

E-print Network

On acoustic cavitation of slightly subcritical bubbles Anthony Harkin Department of Mathematics than the Blake critical radius, in the presence of time-periodic acoustic pressure fields the accuracy of these predictions. Finally, the implications of these findings for acoustic pressure fields

Kaper, Tasso J.

16

Cavitation in confined water: ultra-fast bubble dynamics  

NASA Astrophysics Data System (ADS)

In the hydraulic vessels of trees, water can be found at negative pressure. This metastable state, corresponding to mechanical tension, is achieved by evaporation through a porous medium. It can be relaxed by cavitation, i.e. the sudden nucleation of vapor bubbles. Harmful for the tree due to the subsequent emboli of sap vessels, cavitation is on the contrary used by ferns to eject spores very swiftly. We will focus here on the dynamics of the cavitation bubble, which is of primary importance to explain the previously cited natural phenomena. We use the recently developed method of artificial tress, using transparent hydrogels as the porous medium. Our experiments, on water confined in micrometric hydrogel cavities, show an extremely fast dynamics: bubbles are nucleated at the microsecond timescale. For cavities larger than 100 microns, the bubble ``rings'' with damped oscillations at MHz frequencies, whereas for smaller cavities the oscillations become overdamped. This rich dynamics can be accounted for by a model we developed, leading to a modified Rayleigh-Plesset equation. Interestingly, this model predicts the impossibility to nucleate bubbles above a critical confinement that depends on liquid negative pressure and corresponds to approximately 100 nm for 20 MPa tensions.

Vincent, Olivier; Marmottant, Philippe

2012-02-01

17

Collapse of cavitation bubbles in blood  

NASA Astrophysics Data System (ADS)

The behaviour of a single bubble in blood and in water is studied by using a non-Newtonian model of spherical bubble dynamics. This model considers the compressibility of the liquid surrounding the bubble, the shear-thinning characteristic of liquid viscosity, liquid density and surface tension. It was found that, for values of the maximum bubble radius larger than 10-1 mm, the collapse of a bubble in a constant pressure field in blood is more violent than in water. It suggests that the amount of collateral damage of the biological tissue induced by bubble collapse during high-speed rotational angioplasty and laser-induced angioplasty can be underestimated by experiments in vitro using water as ambient liquid.

Brujan, E.-A.

2000-04-01

18

Unsteady translation and repetitive jetting of acoustic cavitation bubbles  

NASA Astrophysics Data System (ADS)

High-speed recordings reveal peculiar details of the oscillation and translation behavior of cavitation bubbles in the vicinity of an ultrasonic horn tip driven at 20 kHz. In particular, a forward jump during collapse that is due to the rapid reduction of virtual mass is observed. Furthermore, frequently a jetting in the translation direction during the collapse phase is resolved. In spite of strong aspherical deformations and frequent splitting, these bubbles survive the jetting collapse, and they rebound recollecting fragments. Because of incomplete restoration of the spherical shape within the following driving period, higher periodic volume oscillations can occur. This is recognized as a yet unknown source of subharmonic acoustic emission by cavitation bubbles. Numerical modeling can capture the essentials of the unsteady translation.

Nowak, Till; Mettin, Robert

2014-09-01

19

Interaction dynamics of spatially separated cavitation bubbles in water.  

PubMed

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). PMID:21198216

Tinne, Nadine; Schumacher, Silvia; Nuzzo, Valeria; Arnold, Cord L; Lubatschowski, Holger; Ripken, Tammo

2010-01-01

20

Plasma formation and temperature measurement during single-bubble cavitation  

Microsoft Academic Search

Single-bubble sonoluminescence (SBSL1-5) results from the extreme\\u000a temperatures and pressures achieved during bubble compression;\\u000a calculations have predicted(6,7) the existence of a hot, optically\\u000a opaque plasma core(8) with consequent bremsstrahlung radiation(9,10).\\u000a Recent controversial reports(11,12) claim the observation of neutrons\\u000a from deuterium - deuterium fusion during acoustic cavitation(11,12.)\\u000a However, there has been previously no strong experimental evidence for\\u000a the existence of a

David J. Flannigan; Kenneth S. Suslick

2005-01-01

21

Effect of laser-induced cavitation bubble on a thin elastic membrane  

NASA Astrophysics Data System (ADS)

A study of the effects of a cavitation bubble on a thin elastic membrane is presented. A cavitation bubble was produced by focusing a high-energy laser beam near an elastic membrane submerged in water, which corresponds to conditions often encountered in ophthalmology. The bubble effects on the membrane were studied as a function of distance between the bubble and membrane and laser pulse energy. Recordings of bubble dynamics with an ultra-high-speed camera were performed on both sides of the membrane, providing better insight into the mechanisms of membrane rupture. Observations have revealed distinct bubble behavior regimes with respect to coefficient ?. Cavitation bubbles centered on the membrane produce less damage than bubbles shifted slightly away. Significant damages were observed at intermediate distances between the bubble and membrane after bubble collapse, while weaker interactions were recorded at larger distances with less or no damaging effect to the membrane.

Orthaber, U.; Petkovšek, R.; Schille, J.; Hartwig, L.; Hawlina, G.; Drnovšek-Olup, B.; Vre?ko, A.; Poberaj, I.

2014-12-01

22

Numerical Computation of Shock Waves in a Spherical Cloud of Cavitation Bubbles  

Microsoft Academic Search

The nonlinear dynamics of a spherical cloud of cavitation bubbles have been simulated numerically in order to learn more about the physical phenomena occurring in cloud cavitation. A finite cloud of nuclei is subject to a de- crease in the ambient pressure which causes the cloud to cavitate. A subsequent pressure recovery then causes the cloud to collapse. This is

Yi-Chun Wang; Christopher E. Brennen

1999-01-01

23

Cavitation bubble generation and control for HIFU transcranial adaptive focusing  

NASA Astrophysics Data System (ADS)

Brain treatment with High Intensity Focused Ultrasound (HIFU) can be achieved by multichannel arrays through the skull using time-reversal focusing. Such a method requires a reference signal either sent by a real source embedded in brain tissues or computed from a virtual source, using the acoustic properties of the skull deduced from CT images. This noninvasive computational method allows precise focusing, but is time consuming and suffers from unavoidable modeling errors which reduce the accessible acoustic pressure at the focus in comparison with real experimental time-reversal using an implanted hydrophone. Ex vivo simulations with a half skull immersed in a water tank allow us to reach at low amplitude levels a pressure ratio of 83% of the reference pressure (real time reversal) at 1MHz. Using this method to transcranially focus a pulse signal in an agar gel (model for in vivo bubble formation), we induced a cavitation bubble that generated an ultrasonic wave received by the array. Selecting the 1MHz component, the signal was time reversed and re-emitted, allowing 97%±1.1% of pressure ratio to be restored. To target points in the vicinity of the geometrical focus, electronic steering from the reference signal has been achieved. Skull aberrations severely degrade the accessible pressure while moving away from the focus ( ˜90% at 10mm in the focal plane). Nevertheless, inducing cavitation bubbles close to the limit of the primary accessible zone allowed us to acquire multiple references signal to increase the electronic steering area by 50%.

Gâteau, J.; Marsac, L.; Pernot, M.; Aubry, J.-F.; Tanter, M.; Fink, M.

2009-04-01

24

Bubbly cavitating flow generation and investigation of its erosional nature for biomedical applications.  

PubMed

This paper presents a study that investigates the destructive energy output resulting from hydrodynamic bubbly cavitation in microchannels and its potential use in biomedical applications. The research performed in this study includes results from bubbly cavitation experiments and findings showing the destructive effects of bubbly cavitating flow on selected solid specimens and live cells. The bubbles generated by hydrodynamic cavitation are highly destructive at the surfaces of the target medium on which they are carefully focused. The resulting destructive energy output could be effectively used for biomedical treatments, such as destroying kidney stones (renal calculi) or killing cancer cells. Motivated by this potential, the cavitation damage to cancerous cells and material removal from chalk pieces (which possess similar material properties as some kidney stones) was investigated. Our results showed that cavitation could induce damage both on chalk pieces and leukemia/lymphoma cells. We discovered that hydrodynamic cavitation exposure had early and delayed effects on cancer cell survival. Hence, the potential of hydrodynamic bubbly cavitation generated at the microscale for biomedical treatments was revealed using the microchannel configuration as a microorifice (with an inner diameter of 147 ?m and a length of 1.52 cm), which acts as the source of bubbly cavitating flows. PMID:21257370

Ko?ar, Ali; ?e?en, Muhsincan; Oral, Ozlem; Itah, Zeynep; Gozuacik, Devrim

2011-05-01

25

Noise due to extreme bubble deformation near inception of tip vortex cavitation  

Microsoft Academic Search

A study on the tip vortex cavitation inception based on extreme bubble deformation and jet noise is presented. First, two preliminary experiments involving bubble splitting between two plates in the absence of swirl are performed to provide a correlation between the numerically computed splitting\\/jet noise and the measured noise. The bubble behavior and pressure signal predicted by the axisymmetric method

Jin-Keun Choi; Georges L. Chahine

2004-01-01

26

Transcranial ultrasonic therapy based on time reversal of acoustically induced cavitation bubble signature  

E-print Network

]. For transcranial thermal therapy with High Intensity Focused Ultrasound (HIFU), which consists of a local heatingTranscranial ultrasonic therapy based on time reversal of acoustically induced cavitation bubble

Paris-Sud XI, Université de

27

The importance of acoustic cavitation in the sonocrystallisation of ice-high speed observations of a single acoustic bubble  

Microsoft Academic Search

The importance of cavitation bubbles in the nucleation of ice crystals in pure water is examined using a single bubble acoustic levitation and high speed imaging system. The dynamic images have shown that neither air bubbles (manually added to the solution), nor an acoustic pressure wave alone (in the absence of cavitation) is sufficient to cause the nucleation of ice

R. Chow; R. Mettin; B. Lindinger; T. Kurz; W. Lauterborn

2003-01-01

28

Time-resolved measurements of shock-induced cavitation bubbles in liquids  

NASA Astrophysics Data System (ADS)

A novel experimental method for the measurement of cavitation bubble dynamics is presented. The method makes use of a collimated cw HeNe laser beam that is focused onto a photodiode. A cavitation bubble centered in the laser beam leads to refraction and thus changes the diode signal. With sufficient temporal resolution of the measurement, the evolution of the bubble dynamics, and in particular, the collapse, could be well resolved (limitation is only due to diode response and oscilloscope bandwidth). In the present work this is demonstrated with cavitation bubbles generated with high-power nanosecond and femtosecond laser pulses, respectively. Bubble evolution is studied in two different liquids (water and glycerine) and at different temperatures and pressures.

Koch, S.; Garen, W.; Hegedüs, F.; Neu, W.; Reuter, R.; Teubner, U.

2012-08-01

29

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

PubMed Central

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. PMID:18601556

Karpiouk, Andrei B.; Aglyamov, Salavat R.; Bourgeois, Frederic; Ben-Yakar, Adela; Emelianov, Stanislav Y.

2008-01-01

30

On the effect of microbubble injection on cavitation bubble dynamics in liquid mercury  

NASA Astrophysics Data System (ADS)

The effect of microbubble injection has been studied numerically to clarify the role of injected bubbles in the experimentally observed suppression of cavitation in liquid mercury. Recently, we attempted to inject gas microbubbles into liquid mercury in order to mitigate cavitation damage on mercury vessels, a critical issue in spallation neutron sources. From an experimental study using an electromagnetically driven impact test machine and a bubble generator, we found that by injecting microbubbles, the magnitude of the negative pressure generated in liquid mercury is slightly decreased and cavitation damage is remarkably reduced. In this paper, we have performed a numerical study using a multibubble model and experimentally obtained pressure-time curves in order to thoroughly explain the experimental findings. We have found that the observed slight change in negative pressure has a strong impact on cavitation bubble dynamics and was caused by the positive pressure wave that the injected bubbles radiated. Also, we have examined whether the injected microbubbles can cause significant erosion, and found that their collapse intensity is much smaller than that of cavitation bubbles since their expansion ratio is relatively small. Additionally we have examined high-frequency pressure pulses observed experimentally only when microbubbles were injected, and clarified that they are due to the free oscillation of injected bubbles.

Ida, Masato; Naoe, Takashi; Futakawa, Masatoshi

2009-03-01

31

Generation of laser-induced cavitation bubbles with a digital hologram  

PubMed Central

We demonstrate a method using a spatial light modulator (SLM) to generate arbitrary 2-D spatial configurations of laser induced cavitation bubbles. The SLM acts as a phase hologram that controls the light distribution in the focal plane of a microscope objective. We generate cavitation bubbles over an area of 380x380 ?m2 with a 20x microscope objective through absorption of the pulsed laser light in a liquid ink solution. We demonstrate the ability to accurately position up to 34 micrometer sized bubbles using laser energies of 56 ?J. PMID:19581988

Quinto-Su, P. A.; Venugopalan, V.; Ohl, C. D.

2010-01-01

32

Visualization of ultrasound induced cavitation bubbles using the synchrotron x-ray Analyzer Based Imaging technique.  

PubMed

Observing cavitation bubbles deep within tissue is very difficult. The development of a method for probing cavitation, irrespective of its location in tissues, would improve the efficiency and application of ultrasound in the clinic. A synchrotron x-ray imaging technique, which is capable of detecting cavitation bubbles induced in water by a sonochemistry system, is reported here; this could possibly be extended to the study of therapeutic ultrasound in tissues. The two different x-ray imaging techniques of Analyzer Based Imaging (ABI) and phase contrast imaging (PCI) were examined in order to detect ultrasound induced cavitation bubbles. Cavitation was not observed by PCI, however it was detectable with ABI. Acoustic cavitation was imaged at six different acoustic power levels and six different locations through the acoustic beam in water at a fixed power level. The results indicate the potential utility of this technique for cavitation studies in tissues, but it is time consuming. This may be improved by optimizing the imaging method. PMID:25401957

Izadifar, Zahra; Belev, George; Izadifar, Mohammad; Izadifar, Zohreh; Chapman, Dean

2014-12-01

33

A new active cavitation mapping technique for pulsed HIFU applications--bubble Doppler.  

PubMed

In this work, a new active cavitation mapping technique for pulsed high-intensity focused ultrasound (pHIFU) applications termed bubble Doppler is proposed and its feasibility is tested in tissue-mimicking gel phantoms. pHIFU therapy uses short pulses, delivered at low pulse repetition frequency, to cause transient bubble activity that has been shown to enhance drug and gene delivery to tissues. The current gold standard for detecting and monitoring cavitation activity during pHIFU treatments is passive cavitation detection (PCD), which provides minimal information on the spatial distribution of the bubbles. B-mode imaging can detect hyperecho formation, but has very limited sensitivity, especially to small, transient microbubbles. The bubble Doppler method proposed here is based on a fusion of the adaptations of three Doppler techniques that had been previously developed for imaging of ultrasound contrast agents-color Doppler, pulse-inversion Doppler, and decorrelation Doppler. Doppler ensemble pulses were interleaved with therapeutic pHIFU pulses using three different pulse sequences and standard Doppler processing was applied to the received echoes. The information yielded by each of the techniques on the distribution and characteristics of pHIFU-induced cavitation bubbles was evaluated separately, and found to be complementary. The unified approach-bubble Doppler-was then proposed to both spatially map the presence of transient bubbles and to estimate their sizes and the degree of nonlinearity. PMID:25265178

Li, Tong; Khokhlova, Tatiana D; Sapozhnikov, Oleg A; O'Donnell, Matthew; Hwang, Joo Ha

2014-10-01

34

Soap-bubble growth  

Microsoft Academic Search

A simple theory describing the dynamics of two-dimensional arrays of soap bubbles is proposed, and compared with a recent experiment. The average area of bubbles scales linearly at late times. Agreement with experiment is satisfactory, although not conclusive.

M. Marder

1987-01-01

35

Shock wave and cavitation bubble dynamics during photodisruption in ocular media and their dependence on the pulse duration  

Microsoft Academic Search

Shock waves and cavitation bubbles generated by optical breakdown may strongly influence the surgical effect of photodisruptive lasers. We have investigated the shock wave and cavitation bubble effects of femtosecond and picosecond laser pulses generated during photodisruption in corneal tissue and water. Laser pulses with 150 fs duration at approximately 620 nm wavelength have been focused into both corneal tissue

Tibor Juhasz; George Kastis; Carlos G. Suarez; Laszlo Turi; Zsolt Bor; Walter E. Bron

1996-01-01

36

Evidence for hydrogen generation in laser- or spark-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

The growing use of focused lasers or electric sparks to generate cavitation bubbles raises concerns about the possible alteration of gas content during the initiation process and its effect on bubble dynamics. We provide experimental evidence that hydrogen molecules are produced for such plasma-induced bubbles. We performed spectral analysis of the light emitted by the plasma and monitored the dissolved hydrogen concentration in water. The mass of dissolved hydrogen was found proportional to the potential energy of the rebound bubble for both laser and spark methods. Nevertheless, hydrogen concentration was found 2.7 times larger with the spark.

Sato, Takehiko; Tinguely, Marc; Oizumi, Masanobu; Farhat, Mohamed

2013-02-01

37

Investigation of a cavitation bubble between a rigid boundary and a free surface  

NASA Astrophysics Data System (ADS)

When a high-intensity laser pulse is focused into a liquid the energy is converted into mechanical energy via an optodynamic process. The conversion starts with plasma formation; this is followed by shock-wave propagation and the expansion of a cavitation bubble. A cavitation bubble developed near boundaries results in an asymmetrical collapse, with the generation of a liquid jet during the bubble's rebound. In the case of a free surface this liquid jet is directed away from the surface and the oscillation times are prolonged. On the other hand, in the case of a rigid boundary, the liquid jet is directed toward the boundary and the oscillation times are shortened. We present measurements of a cavitation bubble oscillating between a free surface and a rigid boundary using deflections of a laser beam as the optical probe. Shadow photography was used simultaneously as a comparison during the experiments. With the beam-deflection probe we also measured the shortening of the oscillation times near a free surface as well as the prolongation of oscillation times near a rigid boundary. In order to explain this shortening of the cavitation-bubble oscillation times near a free surface, Rayleigh's model was extended and compared with our experimental results.

Gregor?i?, Peter; Petkovšek, Rok; Možina, Janez

2007-11-01

38

The effect of cavitation bubbles on the removal of juvenile barnacles.  

PubMed

The effect of cavitation bubbles on the removal of juvenile barnacles was documented using high speed photography. Using spark generated bubbles, the interaction between barnacle and cavitation bubble was examined in detail. The liquid jet generated by the bubble collapse was observed to be directed towards barnacle at different impact intensities, which is related to the dimensionless distance H' (H'=H/Rm), where H is the distance between bubble formation point and the top of barnacle, and Rm is the maximum bubble radius. At lower values of H', higher speed liquid jet was produced; consequently a larger impact pressure was generated. In general, barnacles are more easily removed at a younger stage. In older barnacles, the liquid jet impact was only able to remove the barnacle shells, leaving the base plate attached to the surface. This study indicates that cavitation can be used to remove attached barnacles, and it would be more efficient if it is applied during early stages of fouling, before the formation of hard calcareous structures. PMID:23643919

Guo, Shifeng; Khoo, Boo Cheong; Teo, Serena Lay Ming; Lee, Heow Pueh

2013-09-01

39

A reduced-order, single-bubble cavitation model with applications to therapeutic ultrasound  

PubMed Central

Cavitation often occurs in therapeutic applications of medical ultrasound such as shock-wave lithotripsy (SWL) and high-intensity focused ultrasound (HIFU). Because cavitation bubbles can affect an intended treatment, it is important to understand the dynamics of bubbles in this context. The relevant context includes very high acoustic pressures and frequencies as well as elevated temperatures. Relative to much of the prior research on cavitation and bubble dynamics, such conditions are unique. To address the relevant physics, a reduced-order model of a single, spherical bubble is proposed that incorporates phase change at the liquid-gas interface as well as heat and mass transport in both phases. Based on the energy lost during the inertial collapse and rebound of a millimeter-sized bubble, experimental observations were used to tune and test model predictions. In addition, benchmarks from the published literature were used to assess various aspects of model performance. Benchmark comparisons demonstrate that the model captures the basic physics of phase change and diffusive transport, while it is quantitatively sensitive to specific model assumptions and implementation details. Given its performance and numerical stability, the model can be used to explore bubble behaviors across a broad parameter space relevant to therapeutic ultrasound. PMID:22088026

Kreider, Wayne; Crum, Lawrence A.; Bailey, Michael R.; Sapozhnikov, Oleg A.

2011-01-01

40

Cavitation and bubble collapse in hot asymmetric nuclear matter  

SciTech Connect

The dynamics of embryonic bubbles in overheated, viscous, and non-Markovian nuclear matter is studied. We show that the memory and the Fermi surface distortions significantly affect the hindrance of bubble collapse and determine characteristic oscillations of the bubble radius. These oscillations occur due to the additional elastic force induced by the memory integral.

Kolomietz, V.M. [Physik-Department TU Muenchen, 85747 Garching (Germany)

2004-10-01

41

Sonoporation of suspension cells with a single cavitation bubble in a microfluidic confinement  

E-print Network

) or molecular delivery. It is widely used in various research areas, such as enzymology, stem cell research of the previous sonoporation experiments have been performed in a bulk solution on a cell suspension, and usingSonoporation of suspension cells with a single cavitation bubble in a microfluidic confinement Se

Ohl, Claus-Dieter

42

Defect structures in nickel and SUS304SS formed by the collapse of cavitation bubbles  

NASA Astrophysics Data System (ADS)

A mercury target in high-power spallation neutron sources is subjected to pressure waves induced by a proton beam. The subsequent formation and collapse of cavitation bubbles lead to cavitation damage on the target vessel, especially the beam window. The cavitation damage in Ni and austenitic stainless steel SUS304SS were studied by using an electro-Magnetic IMpact Testing Machine (MIMTM) developed to simulate the damage. The existence of dislocations, stacking fault tetrahedra and vacancies was detected by positron annihilation lifetime measurements in Ni, and non-cellular dislocation structures were observed by transmission electron microscopy in Ni and SUS304SS. In addition, a high density of twins was observed in SUS304SS. These results were compared with those of high-speed compression tests using a high-speed projectile, proving that the cavitation damage caused by MIMTM corresponded to high-speed deformation.

Yoshiie, T.; Sato, K.; Xu, Q.; Komatsu, M.; Futakawa, M.; Naoe, T.; Kawai, M.

2010-03-01

43

Shock wave and cavitation bubble dynamics during photodisruption in ocular media and their dependence on the pulse duration  

NASA Astrophysics Data System (ADS)

Shock waves and cavitation bubbles generated by optical breakdown may strongly influence the surgical effect of photodisruptive lasers. We have investigated the shock wave and cavitation bubble effects of femtosecond and picosecond laser pulses generated during photodisruption in corneal tissue and water. Laser pulses with 150 fs duration at approximately 620 nm wavelength have been focused into both corneal tissue and water to create optical breakdown. Pulses with durations of 20 ps have been applied for comparative studies. Time-resolved flash photography has been used to investigate the dynamics of the generated shock waves and cavitation bubbles. Femtosecond pulse engender rapidly decaying shock waves in both materials. The spatial range of shock waves induced by femtosecond laser pulses is considerably smaller than that of shock waves induced by picosecond optical breakdown. Cavitation bubbles excited by femtosecond pulses are observed to develop more rapidly and to reach smaller maximum diameter than those generated by longer pulses. In corneal tissue intrastromal cavitation bubbles generated by femtosecond pulses disappear within a few tens of seconds, notably faster than cavitation bubbles generated by picosecond pulses. The reduced shock wave and cavitation bubble effects of the femtosecond laser result in more localized tissue damage. Therefore, a more confined surgical effect should be expected from a femtosecond laser than that from picosecond (or nanosecond) lasers. This indicates a potential benefit from the application of femtosecond laser technology to intraocular microsurgery.

Juhasz, Tibor; Kastis, George; Suarez, Carlos G.; Turi, Laszlo; Bor, Zsolt; Bron, Walter E.

1996-05-01

44

Bubble Growth in Lunar Basalts  

NASA Astrophysics Data System (ADS)

Although Moon is usually said to be volatile-"free", lunar basalts are often vesicular with mm-size bubbles. The vesicular nature of the lunar basalts suggests that they contained some initial gas concentration. A recent publication estimated volatile concentrations in lunar basalts (Saal et al. 2008). This report investigates bubble growth on Moon and compares with that on Earth. Under conditions relevant to lunar basalts, bubble growth in a finite melt shell (i.e., growth of multiple regularly-spaced bubbles) is calculated following Proussevitch and Sahagian (1998) and Liu and Zhang (2000). Initial H2O content of 700 ppm (Saal et al. 2008) or lower is used and the effect of other volatiles (such as carbon dioxide, halogens, and sulfur) is ignored. H2O solubility at low pressures (Liu et al. 2005), concentration-dependent diffusivity in basalt (Zhang and Stolper 1991), and lunar basalt viscosity (Murase and McBirney 1970) are used. Because lunar atmospheric pressure is essentially zero, the confining pressure on bubbles is completely supplied by the overlying magma. Due to low H2O content in lunar basaltic melt (700 ppm H2O corresponds to a saturation pressure of 75 kPa), H2O bubbles only grow in the upper 16 m of a basalt flow or lake. A depth of 20 mm corresponds to a confining pressure of 100 Pa. Hence, vesicular lunar rocks come from very shallow depth. Some findings from the modeling are as follows. (a) Due to low confining pressure as well as low viscosity, even though volatile concentration is very low, bubble growth rate is extremely high, much higher than typical bubble growth rates in terrestrial melts. Hence, mm-size bubbles in lunar basalts are not strange. (b) Because the pertinent pressures are so low, bubble pressure due to surface tension plays a main role in lunar bubble growth, contrary to terrestrial cases. (c) Time scale to reach equilibrium bubble size increases as the confining pressure increases. References: (1) Liu Y, Zhang YX (2000) Earth Planet. Sci. Lett. 181, 251. (2) Liu Y, Zhang YX, Behrens H (2005) J. Volcanol. Geotherm. Res. 143, 219. (3) Murase T, McBirney A (1970) Science 167, 1491. (4) Proussevitch AA, Sahagian DL (1998) J. Geophys. Res. 103, 18223. (5) Saal AE, Hauri EH, Cascio ML, et al. (2008) Nature 454, 192. (6) Zhang YX, Stolper EM (1991) Nature 351, 306.

Zhang, Y.

2009-05-01

45

Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles  

PubMed Central

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip. PMID:23964308

Fernandez Rivas, David; Verhaagen, Bram; Seddon, James R. T.; Zijlstra, Aaldert G.; Jiang, Lei-Meng; van der Sluis, Luc W. M.; Versluis, Michel; Lohse, Detlef; Gardeniers, Han J. G. E.

2012-01-01

46

Interaction of lithotripter shockwaves with single inertial cavitation bubbles.  

PubMed

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave-bubble interaction are discussed. PMID:19018296

Klaseboer, Evert; Fong, Siew Wan; Turangan, Cary K; Khoo, Boo Cheong; Szeri, Andrew J; Calvisi, Michael L; Sankin, Georgy N; Zhong, Pei

2007-01-01

47

Interaction of lithotripter shockwaves with single inertial cavitation bubbles  

PubMed Central

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave–bubble interaction are discussed. PMID:19018296

Klaseboer, Evert; Fong, Siew Wan; Turangan, Cary K.; Khoo, Boo Cheong; Szeri, Andrew J.; Calvisi, Michael L.; Sankin, Georgy N.; Zhong, Pei

2008-01-01

48

Effects of cavitation bubble interaction with temporally separated fs-laser pulses.  

PubMed

We present a time-resolved photographic analysis of the pulse-to-pulse interaction. In particular, we studied the influence of the cavitation bubble induced by a fs-pulse on the optical focusing of the consecutive pulse and its cavitation bubble dynamics in dependence on temporal pulse separation in water. As a first result, by decreasing the temporal separation of laser pulses, there is a diminishment of the laser-induced optical breakdown (LIOB) efficiency in terms of energy conversion, caused by disturbed focusing into persisting gas bubbles at the focal volume. A LIOB at the focal spot is finally suppressed by impinging the expanding or collapsing cavitation bubble of the preceding pulse. These results could be additionally confirmed in porcine gelatin solution with various concentrations. Hence, the interaction between the laser and transparent ophthalmic tissue may be accompanied by a raised central laser energy transmission, which could be observed in case of a temporal pulse overlap. In conclusion, our experimental results are of particular importance for the optimization of the prospective ophthalmic surgical process with future generation fs-lasers. PMID:24781592

Tinne, Nadine; Knoop, Gesche; Kallweit, Nicole; Veith, Sonja; Bleeker, Sebastian; Lubatschowski, Holger; Krüger, Alexander; Ripken, Tammo

2014-04-01

49

Interaction dynamics of temporal and spatial separated cavitation bubbles in water  

NASA Astrophysics Data System (ADS)

The LASIK procedure is a well established laser based treatment in ophthalmology. Nowadays it includes a cutting of the corneal tissue bases on ultra short pulses which are focused below the tissue surface to create an optical breakdown and hence a dissection of the tissue. The energy of the laser pulse is absorbed by non-linear processes that result in an expansion of a cavitation bubble and rupturing of the tissue. Due to a reduction of the duration of treatment the current development of ultra short laser systems points to higher repetition rates. This in turn results in a probable interaction between different cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. We present a high-speed photography analysis of cavitation bubble interaction for two spatial separated laser-induced optical breakdowns varying the laser pulse energy as well as the spatial distance. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape, asymmetric water streams and jet formation were observed. The results of this research can be used to comprehend and optimize the cutting effect of ultra short pulse laser systems with high repetition rates (> 1 MHz).

Tinne, N.; Ripken, T.; Lubatschowski, H.

2010-02-01

50

Dynamic and interaction of fs-laser induced cavitation bubbles for analyzing the cutting effect  

NASA Astrophysics Data System (ADS)

A prominent laser based treatment in ophthalmology is the LASIK procedure which nowadays includes a cutting of the corneal tissue based on ultra short pulses. Focusing an ultra short laser pulse below the surface of biological tissue an optical breakdown is caused and hence a dissection is obtained. The laser energy of the laser pulses is absorbed by nonlinear processes. As a result a cavitation bubble expands and ruptures the tissue. Hence positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the duration of the treatment the current development of ultra short laser systems points to higher repetition rates in the range of hundreds of KHz or even MHz instead of tens of kHz. This in turn results in a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra short pulse laser systems with high (> 1 MHz) repetition rates.

Tinne, N.; Schumacher, S.; Nuzzo, V.; Ripken, T.; Lubatschowski, H.

2009-07-01

51

Single bubble perturbation in cavitation proximity of solid glass: hot spot versus distance.  

PubMed

A systematic study of the energy loss of a cavitation bubble in a close proximity of a glass surface is introduced for the first time in a low acoustic field (1.2-2.4 bar). Single bubble sonoluminescence (SBSL) is used as a tool to predict the temperature and pressure decrease of bubble (?m) versus surface distance. A glass as a model system is used to imitate the boundary conditions relevant for nano- or micromaterials. SBSL preequilibrated with 5% argon is perturbed by a glass rod with the tip (Z-perturbation) and with the long axis (X-perturbation) at a defined distance. From 2 mm to 500 ?m argon-SBSL lines monotonically narrow and the effective emission temperature decreases from 9000 K to 6800 K comparable to multiple bubbles. The electron density decreases by two orders of magnitude in Z-perturbation and is by a factor of two higher in X-perturbation than the unperturbed cavitating bubble. The perturbed single bubble sonoluminescence pressure decreases from 2700 atm to 1200 atm at 2.4 bar. In water new non-SBSL SiO molecular emission lines are observed and OH emission disappears. PMID:24068109

Radziuk, Darya; Möhwald, Helmuth; Suslick, Kenneth

2014-02-28

52

The role of bubbles and cavitation in the production of thermal lesions from high-intensity focused ultrasound  

NASA Astrophysics Data System (ADS)

Rapid hyperthermia resulting in tissue necrosis is a key physical mechanism for focused ultrasound surgery (FUS). At therapeutic intensities, tissue heating is often accompanied by cavitation activity. Although it is well known that bubbles promote mechanical damage, in vitro and in vivo experiments have shown that under certain conditions bubble activity can double the heating rate. With a view towards harnessing bubbles and cavitation for useful clinical work, we report the results of in vitro experiments and modeling for the dynamic and thermal behavior of bubbles subjected to 1-megahertz ultrasound at mega-pascal pressures. The dominant bubble-related heating mechanism depends critically on the bubble size distribution which, in turn, depends on insonation control parameters (acoustic pressure, pulse duration), medium properties (notably dissolved gas concentration), and bubble-destroying shape instabilities. The evidence points to a range of control parameters for which bubble-enhanced FUS can be assured. [Work supported by DARPA and the U.S. Army.

Roy, Ronald A.; Holt, R. Glynn; Yang, Xinmai; Edson, Patrick

2002-11-01

53

Dynamic features of a laser-induced cavitation bubble near a solid boundary.  

PubMed

This paper deals with detailed features of bubble dynamics near a solid boundary. The cavitation bubble was created by using a Q-switched Nd: YAG laser pulse and observed using a high-speed camera (up to 100,000 frames per second). A hydrophone system was employed to monitor the acoustic signals generated by the transient pressure impulses and estimate the bubble oscillation periods. Experimental observations were carried out for bubbles with various maximum expanded radius Rmax (between 1.0mm and 1.6mm) and stand-off distances, ds (defined as the distance between the solid boundary and the bubble center at inception) of 0.4???3.0, and ?=ds/Rmax. The existence of a solid boundary created asymmetry in the flow field and forced the bubble to collapse non-spherically, which finally brought forth the jet impact phenomenon. The dimensionless first and second oscillation periods were dependent on ?. A series of expansion and collapse of the bubble with cascading loss of energy were observed after the bubble had been generated. This study revealed that most bubbles lost about two-thirds of the total energy from the first maximum expansion to the second maximum expansion. PMID:23411165

Yang, Yuan Xiang; Wang, Qian Xi; Keat, T S

2013-07-01

54

Effect of picosecond laser induced cavitation bubbles generated on Au targets in a nanoparticle production set-up  

NASA Astrophysics Data System (ADS)

This work is aimed at an analysis of the influence on the efficiency of nanoparticle production of a cavitation bubble (CB), which forms during the laser ablation process in high-fluence regime. The CB is produced on an Au metal target immersed in water by 1064 nm ps Nd:YAG laser pulses at different fluences. Its time-space evolution is monitored by a shadowgraphic set-up, while the Au nanoparticles production rate is tagged by the growth of the plasmon resonance, which is detected by measuring shot-by-shot the UV-Vis absorbance. We analyze the dependence of bubble size on the experimental parameters. Our results appear of interest to enhance the nanoparticle production efficiency in a liquid medium.

Tiberi, M.; Simonelli, A.; Cristoforetti, G.; Marsili, P.; Giammanco, F.; Giorgetti, E.

2013-03-01

55

Cavitation bubbles induced by Erbium lasers: implications for dentistry  

NASA Astrophysics Data System (ADS)

With new fiber systems available for 3 ?m, Erbium lasers become more interesting for precise tissue ablation in a water environment enabling new application in e.g. dentistry. The dynamics of explosive bubble formation was investigated at 2.78 ?m (Er,Cr;YSGG) and 2.94 ?m (Er:YAG), in relation to energy (10-50 mJ), pulse length (20-150 ?s) and fiber tip shape (flat or taper). The dynamics of exploding and imploding vapor bubbles were captured with high speed imaging (10 - 300 ?s range). Increasing the pulse length and energy, the vapor bubble became more elongated with an opaque surface for flat tip fibers. Tapered fibers produced spherical vapor bubbles with an optically transparent surface expected to be more forceful for creating mechanical effects in both hard and soft tissues. There was no significant difference between bubbles formed at 2.78 ?m (Er,Cr;YSGG) and 2.94 ?m (Er:YAG).

Verleng, Marja; Verdaasdonk, Rudolf; van der Veen, Albert; Lemberg, Vladimir; Boutoussov, Dmitri

2014-02-01

56

Interaction of laser-produced cavitation bubbles with an elastic tissue model  

Microsoft Academic Search

We investigated the interaction of a laser-induced cavitation bubble with an elastic tissue model by high-speed photography with up to 5 Mill. frames\\/sec. The elastic material consisted of a transparent polyacrylamide (PAA) gel whose elastic properties can be controlled by modifying the water content to mimic various biological tissues. The elastic modulus E of the PAA sample was varied between

Alfred Vogel; Emil A. Brujan; Peter Schmidt; Kester Nahen

2001-01-01

57

Reduction of Bubble Cavitation by Modifying the Diffraction Wave from a Lithotripter Aperture  

PubMed Central

Abstract Purpose A new method was devised to suppress the bubble cavitation in the lithotripter focal zone to reduce the propensity of shockwave-induced renal injury. Materials and Methods An edge extender was designed and fabricated to fit on the outside of the ellipsoidal reflector of an electrohydraulic lithotripter to disturb the generation of diffraction wave at the aperture, but with little effect on the acoustic field inside the reflector. Results Although the peak negative pressures at the lithotripter focus using the edge extender at 20?kV were similar to that of the original configuration (-11.1±0.9 vs ?10.6±0.7?MPa), the duration of the tensile wave was shortened significantly (3.2±0.54 vs 5.83±0.56??s, P<0.01). There is no difference, however, in both the amplitude and duration of the compressive shockwaves between these two configurations as well as the ?6 dB beam width in the focal plane. The significant suppression effect of bubble cavitation was confirmed by the measured bubble collapse time using passive cavitation detection. At the lithotripter focus, while only about 30 shocks were needed to rupture a blood vessel phantom using the original HM-3 reflector at 20?kV, no damage could be produced after 300 shocks using the edge extender. Meanwhile, the original HM-3 lithotripter at 20?kV can achieve a stone comminution efficiency of 50.4±2.0% on plaster-of-Paris stone phantom after 200 shocks, which is comparable to that of using the edge extender (46.8±4.1%, P=0.005). Conclusions Modifying the diffraction wave at the lithotripter aperture can suppress the shockwave-induced bubble cavitation with significant reduced damage potential on the vessel phantom but satisfactory stone comminution ability. PMID:22332839

2012-01-01

58

Incubation pit analysis and calculation of the hydrodynamic impact pressure from the implosion of an acoustic cavitation bubble.  

PubMed

An experimental study to evaluate cavitation bubble dynamics is conducted. The aim is to predict the magnitude and statistical distribution of hydrodynamic impact pressure generated from the implosion of various individual acoustic cavitation bubbles near to a rigid boundary, considering geometrical features of the pitted area. A steel sample was subjected to cavitation impacts by an ultrasonic transducer with a 5mm diameter probe. The pitted surface was then examined using high-precision 3D optical interferometer techniques. Only the incubation period where surface is plastically deformed without material loss is taken into account. The exposure time was adjusted in the range of 3-60 s to avoid pit overlapping and a special procedure for pit analysis and characterisation was then followed. Moreover, a high-speed camera device was deployed to capture the implosion mechanisms of cavitation bubbles near to the surface. The geometrical characteristics of single incubation pits as well as pit clusters were studied and their deformation patterns were compared. Consequently, a reverse engineering approach was applied in order the hydrodynamic impact pressure from the implosion of an individual cavitation bubble to be determined. The characteristic parameters of the cavitation implosion process such as hydrodynamic impact pressure and liquid micro-jet impact velocity as well as the hydrodynamic severity of the cavitation impacts were quantified. It was found that the length of the hypotenuse of the orthographic projections from the center of the pit, which basically represents the deformed area of the pit, increases with the hydrodynamic impact aggressiveness in a linear rate. Majority of the hydrodynamic impacts were in the range of 0.4-1 GPa while the corresponding micro-jet velocities were found to be in the range of 200-700 m/s. Outcomes of this study, contribute to further understanding the cavitation intensity from the implosion of acoustically generated bubbles and could certainly represent a significant step towards developing more accurate cavitation models. PMID:24176799

Tzanakis, I; Eskin, D G; Georgoulas, A; Fytanidis, D K

2014-03-01

59

Helium Bubble Injection Solution To The Cavitation Damage At The Spallation Neutron Source  

NASA Astrophysics Data System (ADS)

The Spallation Neutron Source (SNS) is one of the largest science projects in the United States, with total cost near 1.4 Billion Dollars. The limiting factor of the facility had always been assumed to be the lifetime of the target window due to radiation damage. After further investigation, the lifetime of the target was determined not to be limited by radiation damage but by cavitation damage. The cavitation damage derives from pressure waves caused by the beam energy deposition. Vapor bubbles form when low to negative pressures occur in the mercury near the stainless steel target window due to wave interaction with the structure. Collapse of these bubbles can focus wave energy in small liquid jets that erode the window surface. Compressibility of the mercury can be enhanced to reduce the amplitude of the pressure wave caused by the beam energy deposition. To enhance compressibility, small (10 to 30 micron diameter) gas bubbles could be injected into the bulk of the mercury. Solubility and diffusivity parameters of inert gas in mercury are required for a complete mechanical simulation and engineering of these strategies. Using current theoretical models, one obtains a theoretical Henry coefficient of helium in mercury on the order of 3.9E15 Pa-molHg/molHe at 300 K. This low solubility was confirmed by a direct, offline experimental method. Mercury was charged with helium and any pressure change was recorded. Any pressure change was attributed to gas going into solution. Therefore, with the sensitivity of the experiment, a lower limit of 9E12 Pa-molHg/molHe was placed on the mercury-helium system. These values guarantee a stable bubble lifetime needed within the SNS mercury target to mitigate cavitation issues.

Francis, M. W.; Ruggles, A. E.

2009-03-01

60

Asymmetric interface temperature during vapor bubble growth  

NASA Astrophysics Data System (ADS)

We investigate the nucleation, growth, and detachment of single vapor bubbles at the interface microscale. Shear flow is used to investigate pool and convective boiling situations using visible and infrared visualizations. We determine a threshold Reynolds number for the onset of asymmetric interfacial temperatures. Below this threshold, bubble growth is geometrically and thermally symmetric, while above, bubbles no longer grow thermally symmetrically. This is explained by the dominance of convective heat transfer removal over viscous effects at the bubble interface. We experimentally demonstrate asymmetric interfacial temperature profiles that should be taken into account for future bubble growth modeling.

Diana, A.; Castillo, M.; Steinberg, T.; Brutin, D.

2013-07-01

61

Stress wave emission and cavitation bubble dynamics by nanosecond optical breakdown in a tissue phantom  

NASA Astrophysics Data System (ADS)

Stress wave emission and cavitation bubble dynamics after optical breakdown in water and a tissue phantom with Nd: YAG laser pulses of 6 ns duration were investigated both experimentally and numerically to obtain a better understanding of the physical mechanisms involved in plasma-mediated laser surgery. Experimental tools were high-speed photography with 50000 frames s(-1) , and acoustic measurements. The tissue phantom consisted of a transparent polyacrylamide (PAA) gel, the elastic properties of which can be controlled by modifying the water content. Breakdown in water produced a purely compressive stress wave. By contrast, in stiff PAA samples and for sufficiently large pulse energies, the compression wave was followed by an intense tensile wave, similar to the behaviour previously observed in cornea. The elastic/plastic response of the medium led to a significant decrease of the maximum size of the cavitation bubble and to a shortening of its oscillation period which was found to be related to the generation of the tensile stress wave upon breakdown. For increasing elastic modulus of the PAA, both the amplitudes of the bubble oscillation and of the stress wave emitted during bubble collapse decreased until the bubble oscillation was so strongly damped that no collapse stress wave was emitted. Numerical simulations were performed using a spherical model of bubble dynamics which includes the compressibility and elastic/plastic behaviour of the medium, viscosity, density and surface tension. The calculations revealed that consideration of the elastic/plastic behaviour of the medium surrounding the bubble is essential to describe the experimentally observed bipolar shape of the stress wave emitted upon optical breakdown. Water is a poor tissue model because the shape of the emitted stress waves and the bubble dynamics differ strongly for both materials. The mechanical properties of PAA were also found to be quite different from those of tissues. Experimental and numerical results provided evidence that the dynamic mechanical properties relevant for optical breakdown in PAA and tissue differ by as much as two orders of magnitude from the static values. The discovery of a tensile stress wave after optical breakdown in tissue-like media is of great importance for the assessment of collateral damage in laser surgery because biological tissues are much more susceptible to tensile stress than to compressive stress.

Brujan, Emil-Alexandru; Vogel, Alfred

2006-07-01

62

Manipulation and Microrheology of Carbon Nanotubes with Laser-Induced Cavitation Bubbles  

NASA Astrophysics Data System (ADS)

Multiwalled carbon nanotubes (MWCNT) are exposed to a transient and strong liquid jet flow created by a pair of differently sized laser-induced cavitation bubbles. The position and size of the bubbles are controlled with a spatial light modulator within a 15?m thick liquid gap. Depending on the tube’s position with respect to this jet flow, rotation, translation, and a bending deformation is observed with a high-speed camera recording at up to 300 000 frames per second. By measuring the decay time of the respective bending modes we determine the flexural rigidity of MWCNTs to be on the range of 0.45-4.06×10-19Nm2. The average diameter of the MWCNTs is 117.8±6.7nm with a thickness of 4.6±0.75nm, yielding a Young’s modulus between 0.033-0.292 TPa.

Quinto-Su, P. A.; Huang, X. H.; Gonzalez-Avila, S. R.; Wu, T.; Ohl, C. D.

2010-01-01

63

Shock waves and cavitation bubbles in water and isooctane generated by Nd:YAG laser: experimental and theoretical results  

NASA Astrophysics Data System (ADS)

Temporal evolution of laser generated cavitation bubbles and shock waves were studied. Q-switched Nd-Yag laser pulses at 1064 nm are focused into the liquid. An Imager 3 CCD camera with multi exposure mode allows recording of 10 images with minimal exposure delay of 100 ns and minimal exposure time of 100 ns. Illumination is provided by xenon flash lamp for single exposure (shock wave recording) and by halogen lamp for multi exposure mode (bubble recording). Distilled water and a retrograde fluid, isooctane, have been under investigation to identify the differences in the cavitation process and shock wave propagation. The calculation of the shock wave velocities in water and isooctane are based on image recording at constant exposure time of 100 ns and using laser differential interferometry. Strong differences of bubble oscillation were observed in water and isooctane. Gilmore's model is used for numerical simulation of bubble dynamics.

Muller, Milos; Garen, Walter; Koch, Sandra; Marsik, Frantisek; Neu, Walter; Saburov, Eduado

2004-04-01

64

Real-Time Monitoring and Quantitative Evaluation of Cavitation Bubbles Induced by High Intensity Focused Ultrasound Using B-Mode Imaging  

NASA Astrophysics Data System (ADS)

A software-based method is proposed to eliminate the flooding interference strips in B-mode images, and to evaluate the cavitation bubbles generated during high intensity focused ultrasound (HIFU) exposures. In vitro tissue phantoms are exposed to 1.12 MHz HIFU pulses with a fixed 100 Hz pulse repetition frequency. HIFU-induced cavitation bubbles are detected as hyperechoic regions in B-mode images. The temporal evolution of cavitation bubbles, generated by HIFU pulses with varying driving amplitude and pulse length, is analyzed by measuring the time-varying area of the hyperechoic region. The results show that: first, it is feasible to monitor HIFU-induced cavitation bubble activity in real-time using B-mode imaging; second, more cavitation bubbles can be generated with higher acoustic energy delivered; third, the hyperechoic region is observed to shrink gradually after ceasing the HIFU pulses, which indicates the dissolution of cavitation bubbles. This work will be helpful for developing an effective tool to realize real-time monitoring and quantitative evaluation of HIFU-induced cavitation bubble activity using a current commercialized B-mode machine.

Yu, Jie; Chen, Chu-Yi; Chen, Gong; Guo, Xia-Sheng; Ma, Yong; Tu, Juan; Zhang, Dong

2014-03-01

65

Transcranial ultrasonic therapy based on time reversal of acoustically induced cavitation bubble signature  

PubMed Central

Brain treatment through the skull with High Intensity Focused Ultrasound (HIFU) can be achieved with multichannel arrays and adaptive focusing techniques such as time-reversal. This method requires a reference signal to be either emitted by a real source embedded in brain tissues or computed from a virtual source, using the acoustic properties of the skull derived from CT images. This non-invasive computational method focuses with precision, but suffers from modeling and repositioning errors that reduce the accessible acoustic pressure at the focus in comparison with fully experimental time-reversal using an implanted hydrophone. In this paper, this simulation-based targeting has been used experimentally as a first step for focusing through an ex vivo human skull at a single location. It has enabled the creation of a cavitation bubble at focus that spontaneously emitted an ultrasonic wave received by the array. This active source signal has allowed 97%±1.1% of the reference pressure (hydrophone-based) to be restored at the geometrical focus. To target points around the focus with an optimal pressure level, conventional electronic steering from the initial focus has been combined with bubble generation. Thanks to step by step bubble generation, the electronic steering capabilities of the array through the skull were improved. PMID:19770084

Gateau, Jerome; Marsac, Laurent; Pernot, Mathieu; Aubry, Jean-Francois; Tanter, Mickael; Fink, Mathias

2010-01-01

66

Transcranial ultrasonic therapy based on time reversal of acoustically induced cavitation bubble signature.  

PubMed

Brain treatment through the skull with high-intensity focused ultrasound can be achieved with multichannel arrays and adaptive focusing techniques such as time reversal. This method requires a reference signal to be either emitted by a real source embedded in brain tissues or computed from a virtual source, using the acoustic properties of the skull derived from computed tomography images. This noninvasive computational method focuses with precision, but suffers from modeling and repositioning errors that reduce the accessible acoustic pressure at the focus in comparison with fully experimental time reversal using an implanted hydrophone. In this paper, this simulation-based targeting has been used experimentally as a first step for focusing through an ex vivo human skull at a single location. It has enabled the creation of a cavitation bubble at focus that spontaneously emitted an ultrasonic wave received by the array. This active source signal has allowed 97 +/- 1.1% of the reference pressure (hydrophone-based) to be restored at the geometrical focus. To target points around the focus with an optimal pressure level, conventional electronic steering from the initial focus has been combined with bubble generation. Thanks to step-by-step bubble generation, the electronic steering capabilities of the array through the skull were improved. PMID:19770084

Gâteau, Jérôme; Marsac, Laurent; Pernot, Mathieu; Aubry, Jean-Francois; Tanter, Mickaël; Fink, Mathias

2010-01-01

67

An Investigation on the Nature of Micro Cavitation Bubbles on the Movement of Undersea Vessels and Waves  

E-print Network

To further understand their nature, micro cavitation bubbles were systematically diffused around the exterior of a test body (tube) fully submerged in a water tank. The primary purpose was to assess the feasibility of applying micro cavitation as a means of depth control for underwater vehicles, mainly but not limited to submarines. Ideally, the results would indicate the use of micro cavitation as a more efficient alternative to underwater vehicle depth control than the conventional ballast tank method. The current approach utilizes the Archimedes' principle of buoyancy to alter the density of the object affected, making it less than, or greater than the density of the surrounding fluid. However, this process is too slow for underwater vehicles to react to sudden obstacles inherent in their environment. Rather than altering its internal density, this research aimed to investigate the response that would occur if the density of its environment was manipulated instead. In theory, and in a hydrostatic fluid, di...

Anderson, Asalie; Hoffman, Derek; Mancas, Stefan C

2014-01-01

68

Contribution of stress wave and cavitation bubble in evaluation of cell-cell adhesion by femtosecond laser-induced impulse  

NASA Astrophysics Data System (ADS)

When an intense femtosecond laser is focused in a cell culture medium, shock wave, stress wave, and cavitation bubble are generated at the laser focal point. Cell-cell adhesion can be broken at the cellular level by the impacts of these factors. We have applied this breaking of the adhesion to an estimation of the cell-cell adhesion strength. In this application, it is important to identify which of these factors is the dominant factor that breaks the adhesion. Here we investigated this issue using streptavidin-coated microbeads adhering to a biotin-coated substrate as a mimic of the cell-cell adhesion. The results indicated that the break was induced mainly by the stress wave, not by the impact of the cavitation bubble.

Iino, Takanori; Li, Po-Lin; Wang, Wen-Zhe; Deng, Jia-Huei; Lu, Yun-Chang; Kao, Fu-Jen; Hosokawa, Yoichiroh

2014-05-01

69

Contribution of stress wave and cavitation bubble in evaluation of cell-cell adhesion by femtosecond laser-induced impulse  

NASA Astrophysics Data System (ADS)

When an intense femtosecond laser is focused in a cell culture medium, shock wave, stress wave, and cavitation bubble are generated at the laser focal point. Cell-cell adhesion can be broken at the cellular level by the impacts of these factors. We have applied this breaking of the adhesion to an estimation of the cell-cell adhesion strength. In this application, it is important to identify which of these factors is the dominant factor that breaks the adhesion. Here we investigated this issue using streptavidin-coated microbeads adhering to a biotin-coated substrate as a mimic of the cell-cell adhesion. The results indicated that the break was induced mainly by the stress wave, not by the impact of the cavitation bubble.

Iino, Takanori; Li, Po-Lin; Wang, Wen-Zhe; Deng, Jia-Huei; Lu, Yun-Chang; Kao, Fu-Jen; Hosokawa, Yoichiroh

2014-10-01

70

Simulations of shock waves and cavitation bubbles produced in water by picosecond and nanosecond laser pulses  

SciTech Connect

The authors compare numerical simulations of bubble dynamics in water with experiments performed at the Medizinisches Laserzentrum Luebeck. Spatial and temporal features of the laser beam were modeled. Plasma growth was predicted using a moving breakdown model. The authors compare the measured and calculated positions of the shock front and the bubble wall as a function of time after optical breakdown in water. Nd:YAG laser pulses of 30-ps 1-mJ and 6-ns 10-mJ were simulated. The authors have extended previous work in which picosecond deposition was modeled as temporally instantaneous and spatially uniform.

Scammon, R.J.; Chapyak, E.J.; Godwin, R.P. [Los Alamos National Lab., NM (United States); Vogel, A. [Medizinisches Laserzentrum Lueebeck GmbH (Germany)

1998-12-01

71

Jet formation and shock wave emission during collapse of ultrasound-induced cavitation bubbles and their role in the therapeutic applications of high-intensity focused ultrasound  

Microsoft Academic Search

The dynamics of inertial cavitation bubbles produced by short pulses of high-intensity focused ultrasound near a rigid boundary are studied to get a better understanding of the role of jet formation and shock wave emission during bubble collapse in the therapeutic applications of ultrasound. The bubble dynamics are investigated by high-speed photography with up to 2 million frames\\/s and acoustic

T. Ikeda; Y. Matsumoto

2005-01-01

72

Growth laws for 3D soap bubbles  

Microsoft Academic Search

Von Neumann's law for 2D soap froth states that the growth rate of a bubble with n sides is proportional to n-6, and does not depend on other details of its shape. I have generalized this relation to 3D by means of an approximate geometrical model invoking maximal entropy considerations. The resulting generalized growth law is V-1\\/3FdVF\\/dt=scrF(F), where F is

Clément Sire

1994-01-01

73

Some problems of the theory of bubble growth and condensation in bubble chambers  

NASA Technical Reports Server (NTRS)

This work is an attempt to explain the reasons for the discrepancies between the theoretical and experimental values of bubble growth rate in an overheated liquid, and to provide a brief formulation of the main premises of the theory on bubble growth in liquid before making a critical analysis. To simplify the problem, the floating upward of bubbles is not discussed; moreover, the study is based on the results of the theory of the behavior of fixed bubbles.

Tkachev, L. G.

1988-01-01

74

Small Gas Bubble Experiment for Mitigation of Cavitation Damage and Pressure Waves in Short-pulse Mercury Spallation Targets  

SciTech Connect

Populations of small helium gas bubbles were introduced into a flowing mercury experiment test loop to evaluate mitigation of beam-pulse induced cavitation damage and pressure waves. The test loop was developed and thoroughly tested at the Spallation Neutron Source (SNS) prior to irradiations at the Los Alamos Neutron Science Center - Weapons Neutron Research Center (LANSCE-WNR) facility. Twelve candidate bubblers were evaluated over a range of mercury flow and gas injection rates by use of a novel optical measurement technique that accurately assessed the generated bubble size distributions. Final selection for irradiation testing included two variations of a swirl bubbler provided by Japan Proton Accelerator Research Complex (J-PARC) collaborators and one orifice bubbler developed at SNS. Bubble populations of interest consisted of sizes up to 150 m in radius with achieved gas void fractions in the 10^-5 to 10^-4 range. The nominal WNR beam pulse used for the experiment created energy deposition in the mercury comparable to SNS pulses operating at 2.5 MW. Nineteen test conditions were completed each with 100 pulses, including variations on mercury flow, gas injection and protons per pulse. The principal measure of cavitation damage mitigation was surface damage assessment on test specimens that were manually replaced for each test condition. Damage assessment was done after radiation decay and decontamination by optical and laser profiling microscopy with damaged area fraction and maximum pit depth being the more valued results. Damage was reduced by flow alone; the best mitigation from bubble injection was between half and a quarter that of flow alone. Other data collected included surface motion tracking by three laser Doppler vibrometers (LDV), loop wall dynamic strain, beam diagnostics for charge and beam profile assessment, embedded hydrophones and pressure sensors, and sound measurement by a suite of conventional and contact microphones.

Wendel, Mark W [ORNL] [ORNL; Felde, David K [ORNL] [ORNL; Sangrey, Robert L [ORNL] [ORNL; Abdou, Ashraf A [ORNL] [ORNL; West, David L [ORNL] [ORNL; Shea, Thomas J [ORNL] [ORNL; Hasegawa, Shoichi [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Kogawa, Hiroyuki [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Naoe, Dr. Takashi [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Farny, Dr. Caleb H. [Boston University] [Boston University; Kaminsky, Andrew L [ORNL] [ORNL

2014-01-01

75

Mechanical effects of laser-induced cavitation bubble on different geometrical confinements for laser propulsion in water  

NASA Astrophysics Data System (ADS)

Laser propulsions of six kinds of propelled objects in water and air are studied in this paper. The kinetic energy and momentum coupling coefficients gained by the objects after implementation of single laser pulses are investigated experimentally. It is shown that the propulsion effects are better in water than in air. Both in water and in air, the propulsion effects are better if there is a cavity on the laser irradiated surface of the object, and a hemispherical cavity works better than a 90°-conical cavity. A concept of equivalent reference pressure is proposed in this paper. It means that the asymmetry in the liquid induced by a rigid boundary near a spherical or nonspherical oscillating bubble can be approximated as the perturbation induced by a compressive stress wave passing through a bubble in the infinite static liquid. Thus, the collapse time and the pressure surrounding the nonspherical collapsing bubble can be estimated based on the maximum velocity of the liquid jet tip. Experiments also show that cavitation with oscillations and collapse can be induced at the object-water interface on the outside surface of the object head by the penetrating intensive stress wave and the elastic deformation of the object head. The bulging velocity of the object surface is calculated based on the propagation theory of stress waves at medium interfaces.

Han, Bing; Pan, Yun-Xiang; Xue, Ya-Li; Chen, Jun; Shen, Zhong-Hua; Lu, Jian; Ni, Xiao-Wu

2011-03-01

76

A numerical study on the effects of cavitation on orifice flow  

NASA Astrophysics Data System (ADS)

Previous experimental studies have shown better atomization of sprays generated by high-pressure liquid injectors when cavitation occurs inside the nozzle. It has been proposed that the collapse of traveling cavitation bubbles increases the disturbances inside the liquid flow. These disturbances will later trigger the instabilities in the emerged jet and cause a shorter breakup distance. In this paper, effects of cavitation on increasing the disturbances in the flow through the orifice of an atomizer are studied. In previous cavitation models, spherical cavitation bubbles are considered. Here, the cavitation bubbles are allowed to deform as they travel through the orifice. Dynamics of the cavitation bubble, traveling in the separated shear layer in the orifice, is analyzed through a one-way coupling between the orifice flow and bubble dynamics. Effects of shear strain, normal strain, and pressure variation are examined. Three mechanisms are suggested that could be responsible for the increase in disturbances in the flow due to cavitation. These mechanisms are monopole, quadrupole, and vorticities generated during growth and collapse of cavitation bubbles. The effects of these mechanisms are estimated by postprocessing of the solutions to the Navier-Stokes equations to identify monopole and quadrupole behaviors.

Dabiri, S.; Sirignano, W. A.; Joseph, D. D.

2010-04-01

77

Dynamics of shock waves and cavitation bubbles in bilinear elastic-plastic media, and the implications to short-pulsed laser surgery  

NASA Astrophysics Data System (ADS)

The dynamics of shock waves and cavitation bubbles generated by short laser pulses in water and elastic-plastic media were investigated theoretically in order to get a better understanding of their role in short-pulsed laser surgery. Numerical simulations were performed using a spherical model of bubble dynamics which include the elastic-plastic behaviour of the medium surrounding the bubble, compressibility, viscosity, density and surface tension. Breakdown in water produces a monopolar acoustic signal characterized by a compressive wave. Breakdown in an elastic-plastic medium produces a bipolar acoustic signal, with a leading positive compression wave and a trailing negative tensile wave. The calculations revealed that consideration of the tissue elasticity is essential to describe the bipolar shape of the shock wave emitted during optical breakdown. The elastic-plastic response of the medium surrounding the bubble leads to a significant decrease of the maximum size of the cavitation bubble and pressure amplitude of the shock wave emitted during bubble collapse, and shortening of the oscillation period of the bubble. The results are discussed with respect to collateral damage in short-pulsed laser surgery.

Brujan, E.-A.

2005-01-01

78

An Acoustofluidic Micromixer via Bubble Inception and Cavitation from Microchannel Sidewalls  

E-print Network

- ing. However, few of these methods have demonstrated the ability to mix high-viscosity fluids,54.R. China *S Supporting Information ABSTRACT: During the deep reactive ion etching process, the sidewalls cavitation, this acoustofluidic approach demonstrates fast, effective mixing in microfluidics. We

79

Ultrasound measurements of cavitation bubble radius for femtosecond laser-induced breakdown in water  

Microsoft Academic Search

The use of femtosecond lasers in medical applications has significantly increased in recent years. Owing to the low energy threshold of bubble formation, the femtosecond laser breakdown has become an estab- lished tool for precision microsurgery of tissues and cells (1). Ultrasound monitoring of the bubble forma- tion can potentially be a useful tool to control the photodisruption process in

Salavat R. Aglyamov; Andrei B. Karpiouk; Frederic Bourgeois; Adela Ben-Yakar; Stanislav Y. Emelianov

2008-01-01

80

Hot spot conditions during cavitation in water  

SciTech Connect

Liquids irradiated with high-intensity ultrasound undergo acoustic cavitation--the formation, growth, and implosive collapse of bubbles. The energy stored during the growth of the bubble in the rarefaction phase of the acoustic field is released when the bubble violently collapses in the compression phase of the acoustic field, as acoustic noise, shock waves, chemical reactions, and the emission of light (sonoluminescence, SL). This violent collapse is predicted to generate a hot spot of thousands of Kelvin within the bubble, but, to date, there have been only a limited number of experimental measurements of the temperature of this hot spot. Although the SL of water has been studied for more than 50 years, the effective hot spot temperature during aqueous cavitation remains unresolved. Given the importance of aqueous cavitation (sonography and bioeffects of ultrasound, sonochemical remediation of aqueous pollutants, synthetic applications of sonochemistry, etc.), the authors decided to apply previous spectroscopic analysis of SL of nonaqueous liquids to aqueous solutions doped with small amounts of hydrocarbons. The authors have collected and analyzed excited-state C{sub 2} NBSL (multi-bubble sonoluminescence, light emission from the clouds of cavitating bubbles) spectra from mixtures of organic liquids in water at 20 kHz and find an effective emission temperature of 4,300 {+-} 200 K.

Didenko, Y.T.; McNamara, W.B. III; Suslick, K.S.

1999-06-23

81

Bubble growth during decompression of magma: experimental and theoretical investigation  

E-print Network

simulations and experimental results on bubble growth during decompression of hydrated silicic melts. Keywords: bubble growth; decompression; viscosity; di¡usion; magma 1. Introduction Volcanic eruptions. Lyakhovsky). Journal of Volcanology and Geothermal Research 129 (2004) 7^22 R Available online at www

Lyakhovsky, Vladimir

82

Interaction dynamics of fs-laser induced cavitation bubbles and their impact on the laser-tissue-interaction of modern ophthalmic laser systems  

NASA Astrophysics Data System (ADS)

A today well-known laser based treatment in ophthalmology is the LASIK procedure which nowadays includes cutting of the corneal tissue with ultra-short laser pulses. Instead of disposing a microkeratome for cutting a corneal flap, a focused ultra-short laser pulse is scanned below the surface of biological tissue causing the effect of an optical breakdown and hence obtaining a dissection. Inside the tissue, the energy of the laser pulses is absorbed by non-linear processes; as a result a cavitation bubble expands and ruptures the tissue. Hence, positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the amount of laser energy, with a moderate duration of treatment at the same time, the current development of ultra-short pulse laser systems points to higher repetition rates in the range of even Megahertz instead of tens or hundreds of Kilohertz. In turn, this results in a pulse overlap and therefor a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus, the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. The effects will be discussed regarding the medical ophthalmic application of fs-lasers. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra-short pulse laser systems with high (> 500 kHz) repetition rates.

Tinne, N.; Ripken, T.; Lubatschowski, H.; Heisterkamp, A.

2011-07-01

83

Bubble dynamics in boiling under high heat flux pulse heating  

Microsoft Academic Search

A new theoretical model of bubble behavior in boiling water under high heat flux pulse is presented. The essence of the model is nucleation in the superheated liquid followed by instantaneous formation of a vapor film, rapid bubble growth due to the pressure impulse, and cavitation bubble collapse. To check the model, boiling of methanol under 5 â¼ 50 MW

A. Asai

1991-01-01

84

{open_quotes}Bubble fusion{close_quotes}: Preliminary estimates of spherical micro-implosions in cavitating liquids  

SciTech Connect

Liquids irradiated with intense ultrasonic waves can generate small cavities or bubbles. Upon nonlinear expansion to a state of disequilibrium, wherein the externally imposed hydrostatic pressure far exceeds that of entrapped non-condensable gas, these bubbles undergo a rapid and violent collapse. This collapse, if symmetric, can generate high pressures and temperatures through a number of possible mechanisms. The simplest and oldest explanation suggests a focusing of the kinetic energy of all the surrounding liquid onto the collapsing bubble and the subsequent heating of entrapped gases under either adiabatic or isothermal conditions. Although induced by externally imposed millisecond pressure oscillations, these collapses can occur on sub-microsecond timescales and are accompanied by picosecond light emissions; this combination of sound and light is called sonoluminescence. Recent explanations of observed high temperatures and picosecond radiation pulses accompanying such collapses are based on the interaction of multiple shock waves that are launched off the inward cavity wall. Other potential explanations invoke dipole emissions induced by intermolecular collisions or the release of Casimir energy when a dielectric hole is filled. Conjectures have been made that the processes responsible for sonoluminescence may be extended to generated conditions where thermonuclear fusion might occur. Such an achievement would extend scientific interest in sonoluminescence out of a purely chemical context to include the study of matter subjected to more extreme conditions. The main goal of this {open_quotes}scoping{close_quotes} study is to understand better conditions where deuterium-tritium fusion might be observed in conjunction with micro-implosions in cavitating liquids; prognoses of fusion application at this point are unintended.

Krakowski, R.A.

1995-02-01

85

Unorthodox bubbles when boiling in cold water  

NASA Astrophysics Data System (ADS)

High-speed movies are taken when bubbles grow at gold surfaces heated spotwise with a near-infrared laser beam heating water below the boiling point (60-70 °C) with heating powers spanning the range from very low to so high that water fails to rewet the surface after bubbles detach. Roughly half the bubbles are conventional: They grow symmetrically through evaporation until buoyancy lifts them away. Others have unorthodox shapes and appear to contribute disproportionately to heat transfer efficiency: mushroom cloud shapes, violently explosive bubbles, and cavitation events, probably stimulated by a combination of superheating, convection, turbulence, and surface dewetting during the initial bubble growth. Moreover, bubbles often follow one another in complex sequences, often beginning with an unorthodox bubble that stirs the water, followed by several conventional bubbles. This large dataset is analyzed and discussed with emphasis on how explosive phenomena such as cavitation induce discrepancies from classical expectations about boiling.

Parker, Scott; Granick, Steve

2014-01-01

86

Unorthodox bubbles when boiling in cold water.  

PubMed

High-speed movies are taken when bubbles grow at gold surfaces heated spotwise with a near-infrared laser beam heating water below the boiling point (60-70?°C) with heating powers spanning the range from very low to so high that water fails to rewet the surface after bubbles detach. Roughly half the bubbles are conventional: They grow symmetrically through evaporation until buoyancy lifts them away. Others have unorthodox shapes and appear to contribute disproportionately to heat transfer efficiency: mushroom cloud shapes, violently explosive bubbles, and cavitation events, probably stimulated by a combination of superheating, convection, turbulence, and surface dewetting during the initial bubble growth. Moreover, bubbles often follow one another in complex sequences, often beginning with an unorthodox bubble that stirs the water, followed by several conventional bubbles. This large dataset is analyzed and discussed with emphasis on how explosive phenomena such as cavitation induce discrepancies from classical expectations about boiling. PMID:24580324

Parker, Scott; Granick, Steve

2014-01-01

87

Vol. 22, No. 3, Aug. 1, 2002 Scientists measure energy dissipation in a single cavitating bubble  

E-print Network

applications, such as the breakdown of pollutants, development of medical imaging agents, and making catalysts. The ability of ultrasound to induce chemical reactions has been studied for industrial and medical that boiling water makes on the stove. To study the energy dissipation during bubble collapse, Suslick

Suslick, Kenneth S.

88

Nucleate boiling bubble growth and departure  

E-print Network

The vapor bubble formation on the heating surface during pool boiling has been studied experimentally. Experiments were made at the atmospheric pressure 28 psi and 40 psi, using degassed distilled water and ethanol. The ...

Staniszewski, Bogumil E.

1959-01-01

89

Source Mergers and Bubble Growth During Reionization  

E-print Network

The recently introduced models of reionization bubbles based on extended Press-Schechter theory (Furlanetto, Zaldarriaga & Hernquist 2004) are generalized to include mergers of ionization sources. Sources with a recent major merger are taken to have enhanced photon production due to star formation, and accretion onto a central black hole if a black hole is present. This produces a scatter in the number of ionized photons corresponding to a halo of a given mass and a change in photon production over time for any given halo mass. Photon production histories, bubble distributions, and ionization histories are computed for several different parameter and recombination assumptions; the resulting distributions interpolate between previously calculated limiting cases.

J. D. Cohn; Tzu-Ching Chang

2006-03-16

90

Single Cavitation Bubble Dynamics in Shear Flow of Water and Dilute Polymer Solution Near a Solid Boundary  

Microsoft Academic Search

Cavitation in hydraulic machinery and in marine applications produces noise, destructive erosion and loss of efficiency. Their fundamental mechanisms, particularly of erosive damage, are not well established. High molecular weight polymer solutions at drag-reducing concentrations substantially alter macroscopic cavitation behaviors such as the inception point, the noise spectrum and the rate of damage. Again, causes are poorly understood. To examine

Martin Robert Wittmann

1992-01-01

91

Interferometric and Shadowgraphic Studies Of Shock Wave And Cavitation Bubble Generated With Nd: YAG Nano Second Laser Pulses Induced Breakdown In Water  

NASA Astrophysics Data System (ADS)

Laser break down and subsequent plasma formation in liquids, in particular in water is of considerable interest due to its potential application in biomedical applications and also in the generation of micro/nano particle formation. There are two mechanisms which can lead to plasma formation: direct ionization of the medium by multiphoton absorption or avalanche ionization via inverse bremsstrahlung absorption. Spectroscopic investigation was performed in the early stage of breakdown of water at and beyond breakdown threshold and subsequent formation of shock waves and cavitation bubble is studied using shadow graphic and interferometric technique.

lakshmi, B. Sita; Leela, Ch.; Bagchi, Suman; Kiran, P. Prem; Prashant, T. S.; Tewari, S. P.; Ashoka, V. S.

2011-10-01

92

Bubble Evolution and Properties in Homogeneous Nucleation Simulations  

E-print Network

We analyze the properties of naturally formed nano-bubbles in Lennard-Jones molecular dynamics simulations of liquid-to-vapor nucleation in the boiling and the cavitation regimes. The large computational volumes provide a realistic environment at unchanging average temperature and liquid pressure, which allows us to accurately measure properties of bubbles from their inception as stable, critically sized bubbles, to their continued growth into the constant speed regime. Bubble gas densities are up to 50$\\%$ lower than the equilibrium vapor densities at the liquid temperature, yet quite close to the gas equilibrium density at the lower gas temperatures measured in the simulations: The latent heat of transformation results in bubble gas temperatures up to 25$\\%$ below those of the surrounding bulk liquid. In the case of rapid bubble growth - typical for the cavitation regime - compression of the liquid outside the bubble leads to local temperature increases of up to 5$\\%$, likely significant enough to alter the...

Angélil, Raymond; Tanaka, Kyoko; Tanaka, Hidekazu

2014-01-01

93

Luminescence of transient single cavitation bubbles in non-aqueous liquids produced by the modified tube-arrest method  

NASA Astrophysics Data System (ADS)

Large transient single bubbles of effective diameters in centimetres were generated by the modified tube-arrest method in 7 nonaqueous liquids besides water and in glycerin-water mixtures. During collapse, nearly all these bubbles gave off light emissions of various intensities, which in 6 liquids were correlated with the saturation vapour pressure and viscosity of the respective liquid. Bubbles in ethylene glycol and propylene glycol did not follow this rule, but those in the former liquid showed some unusual regularity in luminescence variation and the bubbles in both the liquids were particularly bright. The luminous properties of the transient single bubble are compared with those of the usual stable single bubble.

Wu, Xian-Mei; Ying, Chong-Fu; Li, Chao

2005-05-01

94

The dynamics of histotripsy bubbles  

NASA Astrophysics Data System (ADS)

Histotripsy describes treatments in which high-amplitude acoustic pulses are used to excite bubbles and erode tissue. Though tissue erosion can be directly attributed to bubble activity, the genesis and dynamics of bubbles remain unclear. Histotripsy lesions that show no signs of thermal coagulative damage have been generated with two different acoustic protocols: relatively long acoustic pulses that produce local boiling within milliseconds and relatively short pulses that are higher in amplitude but likely do not produce boiling. While these two approaches are often distinguished as `boiling' versus `cavitation', such labels can obscure similarities. In both cases, a bubble undergoes large changes in radius and vapor is transported into and out of the bubble as it oscillates. Moreover, observations from both approaches suggest that bubbles grow to a size at which they cease to collapse violently. In order to better understand the dynamics of histotripsy bubbles, a single-bubble model has been developed that couples acoustically excited bubble motions to the thermodynamic state of the surrounding liquid. Using this model for bubbles exposed to histotripsy sound fields, simulations suggest that two mechanisms can act separately or in concert to lead to the typically observed bubble growth. First, nonlinear acoustic propagation leads to the evolution of shocks and an asymmetry in the positive and negative pressures that drive bubble motion. This asymmetry can have a rectifying effect on bubble oscillations whereby the bubble grows on average during each acoustic cycle. Second, vapor transport to/from the bubble tends to produce larger bubbles, especially at elevated temperatures. Vapor transport by itself can lead to rectified bubble growth when the ambient temperature exceeds 100 °C (`boiling') or local heating in the vicinity of the bubble leads to a superheated boundary layer.

Kreider, Wayne; Bailey, Michael R.; Sapozhnikov, Oleg A.; Khokhlova, Vera A.; Crum, Lawrence A.

2011-09-01

95

Luminescence of transient single cavitation bubbles in non-aqueous liquids produced by the modified tube-arrest method  

Microsoft Academic Search

Large transient single bubbles of effective diameters in centimetres were generated by the modified tube-arrest method in 7 nonaqueous liquids besides water and in glycerin-water mixtures. During collapse, nearly all these bubbles gave off light emissions of various intensities, which in 6 liquids were correlated with the saturation vapour pressure and viscosity of the respective liquid. Bubbles in ethylene glycol

Xian-Mei Wu; Chong-Fu Ying; Chao Li

2005-01-01

96

THE NUCLEATION AND GROWTH OF GAS BUBBLES IN A NEWTONIAN FLUID: AN ENERGETIC VARIATIONAL PHASE  

E-print Network

THE NUCLEATION AND GROWTH OF GAS BUBBLES IN A NEWTONIAN FLUID: AN ENERGETIC VARIATIONAL PHASE FIELD and growth of gas bubbles in a Newtonian fluid. We employ a general energetic variational formulation with those of classical models. The new approach allows the study of bubble nucleation, growth

Feng, James J.

97

Bubbles  

NASA Astrophysics Data System (ADS)

Vanitas vanitatum et omnia vanitas: bubbles are emptiness, non-liquid, a tiny cloud shielding a mathematical singularity. Born from chance, a violent and brief life ending in the union with the (nearly) infinite. But a wealth of phenomena spring forth from this nothingness: underwater noise, sonoluminescence, boiling, and many others. Some recent results on a "blinking bubble" micropump and vapor bubbles in sound fields are outlined. The last section describes Leonardo da Vinci's observation of the non-rectlinear ascent of buoyant bubbles and justifies the name Leonardo's paradox recently attributed to this phenomenon.

Prosperetti, Andrea

2004-06-01

98

Cavitation in a metallic liquid: homogeneous nucleation and growth of nanovoids.  

PubMed

Large-scale molecular dynamics (MD) simulations are performed to investigate homogeneous nucleation and growth of nanovoids during cavitation in liquid Cu. We characterize in detail the atomistic cavitation processes by following the temporal evolution of cavities or voids, analyze the nucleation behavior with the mean first-passage time (MFPT) and survival probability (SP) methods, and discuss the results against classical nucleation theory (CNT), the Tolman equation for surface energy, independent calculation of surface tension via integrating the stress profiles, the Johnson-Mehl-Avrami (JMA) growth law, and the power law for nucleus size distributions. Cavitation in this representative metallic liquid is a high energy barrier Poisson processes, and the steady-state nucleation rates obtained from statistical runs with the MFPT and SP methods are in agreement. The MFPT method also yields the critical nucleus size and the Zeldovich factor. Fitting with the Tolman's equation to the MD simulations yields the surface energy of a planar interface (~0.9 J m?²) and the Tolman length (0.4-0.5 Å), and those values are in accord with those from integrating the stress profiles of a planar interface. Independent CNT predictions of the nucleation rate (10(33 - 34) s(-1) m(-3)) and critical size (3-4 Å in radius) are in agreement with the MFPT and SP results. The JMA law can reasonably describe the nucleation and growth process. The size distribution of subcritical nuclei appears to follow a power law with an exponent decreasing with increasing tension owing to coupled nucleation and growth, and that of the supercritical nuclei becomes flattened during further stress relaxation due to void coalescence. PMID:24908018

Cai, Y; Wu, H A; Luo, S N

2014-06-01

99

Cavitation in a metallic liquid: Homogeneous nucleation and growth of nanovoids  

NASA Astrophysics Data System (ADS)

Large-scale molecular dynamics (MD) simulations are performed to investigate homogeneous nucleation and growth of nanovoids during cavitation in liquid Cu. We characterize in detail the atomistic cavitation processes by following the temporal evolution of cavities or voids, analyze the nucleation behavior with the mean first-passage time (MFPT) and survival probability (SP) methods, and discuss the results against classical nucleation theory (CNT), the Tolman equation for surface energy, independent calculation of surface tension via integrating the stress profiles, the Johnson-Mehl-Avrami (JMA) growth law, and the power law for nucleus size distributions. Cavitation in this representative metallic liquid is a high energy barrier Poisson processes, and the steady-state nucleation rates obtained from statistical runs with the MFPT and SP methods are in agreement. The MFPT method also yields the critical nucleus size and the Zeldovich factor. Fitting with the Tolman's equation to the MD simulations yields the surface energy of a planar interface (˜0.9 J {m}^{-2}) and the Tolman length (0.4-0.5 Å), and those values are in accord with those from integrating the stress profiles of a planar interface. Independent CNT predictions of the nucleation rate (1033 - 34 s-1 m-3) and critical size (3-4 Å in radius) are in agreement with the MFPT and SP results. The JMA law can reasonably describe the nucleation and growth process. The size distribution of subcritical nuclei appears to follow a power law with an exponent decreasing with increasing tension owing to coupled nucleation and growth, and that of the supercritical nuclei becomes flattened during further stress relaxation due to void coalescence.

Cai, Y.; Wu, H. A.; Luo, S. N.

2014-06-01

100

Vulnerability to cavitation, hydraulic efficiency, growth and survival in an insular pine (Pinus canariensis)  

PubMed Central

Background and Aims It is widely accepted that hydraulic failure due to xylem embolism is a key factor contributing to drought-induced mortality in trees. In the present study, an attempt is made to disentangle phenotypic plasticity from genetic variation in hydraulic traits across the entire distribution area of a tree species to detect adaptation to local environments. Methods A series of traits related to hydraulics (vulnerability to cavitation and hydraulic conductivity in branches), growth performance and leaf mass per area were assessed in eight Pinus canariensis populations growing in two common gardens under contrasting environments. In addition, the neutral genetic variability (FST) and the genetic differentiation of phenotypic variation (QST) were compared in order to identify the evolutionary forces acting on these traits. Key Results The variability for hydraulic traits was largely due to phenotypic plasticity. Nevertheless, the vulnerability to cavitation displayed a significant genetic variability (approx. 5 % of the explained variation), and a significant genetic × environment interaction (between 5 and 19 % of the explained variation). The strong correlation between vulnerability to cavitation and survival in the xeric common garden (r = –0·81; P < 0·05) suggests a role for the former in the adaptation to xeric environments. Populations from drier sites and higher temperature seasonality were less vulnerable to cavitation than those growing at mesic sites. No trade-off between xylem safety and efficiency was detected. QST of parameters of the vulnerability curve (0·365 for P50 and the slope of the vulnerability curve and 0·452 for P88) differed substantially from FST (0·091), indicating divergent selection. In contrast, genetic drift alone was found to be sufficient to explain patterns of differentiation for xylem efficiency and growth. Conclusions The ability of P. canariensis to inhabit a wide range of ecosystems seemed to be associated with high phenotypic plasticity and some degree of local adaptations of xylem and leaf traits. Resistance to cavitation conferred adaptive potential for this species to adapt successfully to xeric conditions. PMID:23644361

Lopez, Rosana; Lopez de Heredia, Unai; Collada, Carmen; Cano, Francisco Javier; Emerson, Brent C.; Cochard, Herve; Gil, Luis

2013-01-01

101

Gas Bubble Growth Dynamics in a Supersaturated Solution: Henry's and Sievert's Solubility Laws  

E-print Network

Theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution is presented. We study the influence of Laplace pressure on the bubble growth. We consider two different solubility laws: Henry's law, which is fulfilled for the systems where no gas molecules dissociation takes place and Sievert's law, which is fulfilled for the systems where gas molecules completely dissociate in the solvent into two parts. We show that the difference between Henry's and Sievert's laws for chemical equilibrium conditions causes the difference in bubble growth dynamics. Assuming that diffusion flux of dissolved gas molecules to the bubble is steady we obtain differential equations on bubble radius for both solubility laws. For the case of homogeneous nucleation of a bubble, which takes place at a significant pressure drop bubble dynamics equations for Henry's and Sievert's laws are solved analytically. For both solubility laws three characteristic stages of bubble growth are mar...

Gor, Gennady Yu; Kuni, Fedor M

2012-01-01

102

Cavitation cluster dynamics in shock-wave lithotripsy: part 1. Free field.  

PubMed

The spatiotemporal dynamics of cavitation bubble growth and collapse in shock-wave lithotripsy in a free field was studied experimentally. The lithotripter was equipped with two independently triggerable layers of piezoceramics. The front and back layers generated positive pressure amplitudes of 30 MPa and 15 MPa, respectively, and -10 MPa negative amplitude. The time interval between the launch of the shock waves was varied from 0 and 0.1 s, covering the regimens of pulse-modification (regimen A, delay 0 to 4 micros), shock wave-cavitation cluster interaction (B, 4 micros to 64 micros) and shock wave-gas bubble interaction (C, 256 micros to 0.1 s). The time-integrated cavitation activity was most strongly influenced in regimen A and, in regimen B, the spatial distribution of bubbles was altered, whereas enhancement of cavitation activity was observed in regimen C. Quantitative measurements of the spatial- and time-integrated void fractions were obtained with a photographic and light-scattering technique. The preconditions for a reproducible experiment are explained, with the existence of two distinct types of cavitation nuclei, small particles suspended in the liquid and residuals of bubbles from prior cavitation clusters. PMID:15936498

Arora, M; Junge, L; Ohl, C D

2005-06-01

103

Taming Acoustic Cavitation  

E-print Network

In this fluid dynamics video we show acoustic cavitation occurring from pits etched on a silicon surface. By immersing the surface in a liquid, gas pockets are entrapped in the pits which upon ultrasonic insonation, are observed to shed cavitation bubbles. Modulating the driving pressure it is possible to induce different behaviours based on the force balance that determines the interaction among bubbles and the silicon surface. This system can be used for several applications like sonochemical water treatment, cleaning of surfaces with deposited materials such as biofilms.

Rivas, David Fernandez; Enriquez, Oscar R; Versluis, Michel; Prosperetti, Andrea; Gardeniers, Han; Lohse, Detlef

2012-01-01

104

Water diffusion, Viscosity and Bubble Growth in Silicate Melts  

NASA Astrophysics Data System (ADS)

For quantitative modeling of bubble growth and volcanic eruption dynamics, it is necessary to know H2O diffusivity in the melt. Over the years, we have been experimentally and systematically investigating H2O diffusion in rhyolite, dacite, andeside, basalt, and a per-alkaline rhyolite (1-7; as well as work in progress). We have also investigated viscosity of hydrous melts and developed a viscosity model for all natural silicate melts (8-10). In this report, we discuss the compositional dependence of H2O diffusivity and the relation between H2O diffusivity and viscosity. Furthermore, we explore how these parameters affect bubble growth rate in various melts. Experimental data show that in contrast to the large differences in viscosity of various melts, the variation of H2O diffusivity with melt composition is in general small, especially at super-liquidus temperatures. For example, when per-alkaline rhyolite is compared with calc-alkaline rhyolite, the viscosity difference is large but the diffusivity difference is small. Comparison between rhyolite and dacite is more complicated. At 1423 K (super-liquidus) and 1.0 wt percent total H2O, the viscosity decreases by a factor of 80 from rhyolite to dacite, but the diffusivity increases by less than a factor of 2. However, at 873 K (sub- liquidus) and 1.0 wt percent total H2O, the difference in the calculated viscosities of rhyolite and dacite is negligible, but the diffusivity decreases by a factor of 6 from rhyolite to dacite. Hence, there does not seem to be a consistent relation between viscosity and H2O diffusivity. When modeling bubble growth rate in different melts, the effect of viscosity variation can change bubble growth rate significantly, but the effect due to variation in diffusivity is small at super-liquidus temperatures. References: (1) Behrens et al. (2004) Geochim. Cosmochim. Acta, 68, 5139-5150. (2) Behrens et al. (2007) Earth Planet. Sci. Lett., 254, 69-76. (3) Liu et al. (2004) Chem. Geol., 209, 327-340. (4) Ni and Zhang (2008) Chem. Geol., 250, 68-78. (5) Zhang et al. (1991) Geochim. Cosmochim. Acta, 55, 441-456. (6) Zhang and Stolper (1991) Nature, 351, 306-309. (7) Zhang and Behrens (2000) Chem. Geol., 169, 243-262. (8) Zhang et al. (2003) Am. Mineral., 88, 1741-1752. (9) Zhang and Xu (2007) Geochim. Cosmochim. Acta, 71, 5226-5232. (10) Hui and Zhang (2007) Geochim. Cosmochim. Acta, 71, 403-416.

Zhang, Y.

2008-12-01

105

Numerical method for predicting ship propeller cavitation noise  

Microsoft Academic Search

During ship travels in high-velocity, propeller cavitation noise predominates in the radiated noise sources. However, experiential data regress method was use to predicate propeller cavitation noise in the past. In this article, propeller cavitation noise has been calculated by numerical computation method. From the engineering point of view, ship propeller has been disposed as a dipole bubble. Bubble volume pulse

Yong-Kun Zhang; Ying Xiong

2011-01-01

106

Bubbles  

NASA Astrophysics Data System (ADS)

``Vanitas vanitatum et omnia vanitas": bubbles are emptiness, non-liquid, a tiny cloud shielding a mathematical singularity. Born from chance, a violent and brief life ending in the union with the (nearly) infinite. But a wealth of phenomena spring forth from this nothingness: underwater noise, sonoluminescence, boiling, many others. Ultimately, diffusive processes govern much of the physics, and the difference between the diffusivity of heat and dissolved gases in ordinary liquids holds the key to the striking differences between gas and vapor bubbles.

Prosperetti, Andrea

2002-11-01

107

Aspherical bubble dynamics and oscillation times  

SciTech Connect

The cavitation bubbles common in laser medicine are rarely perfectly spherical and are often located near tissue boundaries, in vessels, etc., which introduce aspherical dynamics. Here, novel features of aspherical bubble dynamics are explored. Time-resolved experimental photographs and simulations of large aspect ratio (length:diameter {approximately}20) cylindrical bubble dynamics are presented. The experiments and calculations exhibit similar dynamics. A small high-pressure cylindrical bubble initially expands radially with hardly any axial motion. Then, after reaching its maximum volume, a cylindrical bubble collapses along its long axis with relatively little radial motion. The growth-collapse period of these very aspherical bubbles differs only sightly from twice the Rayleigh collapse time for a spherical bubble with an equivalent maximum volume. This fact justifies using the temporal interval between the acoustic signals emitted upon bubble creation and collapse to estimate the maximum bubble volume. As a result, hydrophone measurements can provide an estimate of the bubble energy even for aspherical bubbles. The prolongation of the oscillation period of bubbles near solid boundaries relative to that of isolated spherical bubbles is also discussed.

Godwin, R.P.; Chapyak, E.J. [Los Alamos National Lab., NM (United States); Noack, J.; Vogel, A. [Medizinisches Laserzentrum Luebeck (Germany)

1999-03-01

108

Plasma and Cavitation Dynamics during Pulsed Laser Microsurgery invivo  

NASA Astrophysics Data System (ADS)

We compare the plasma and cavitation dynamics underlying pulsed laser microsurgery in water and in fruit fly embryos (in vivo)—specifically for nanosecond pulses at 355 and 532 nm. We find two key differences. First, the plasma-formation thresholds are lower in vivo —especially at 355 nm—due to the presence of endogenous chromophores that serve as additional sources for plasma seed electrons. Second, the biological matrix constrains the growth of laser-induced cavitation bubbles. Both effects reduce the disrupted region in vivo when compared to extrapolations from measurements in water.

Hutson, M. Shane; Ma, Xiaoyan

2007-10-01

109

Collapsing cavities, toroidal bubbles and jet impact  

NASA Astrophysics Data System (ADS)

The present study is aimed at clarifying some of the factors which affect the formation and direction of a liquid jet in a collapsing cavity and the pressures induced on a nearby rigid boundary. The flow can be accurately represented by a velocity potential leading to the use of boundary integral methods to compute bubble collapse. For configurations with axial symmetry, the jet motion and that of the bubble centroid are along the axis of symmetry. Examples are presented for bubbles close to a rigid surface and to a free surface. These are followed through to the toroidal stage after jet penetration. When there is no axis of symmetry, fully three-dimensional computations show that the buoyancy force can cause the jet to move parallel to a vertical rigid boundary, thus negating its damaging effect. The computational study is extended to model cavitation bubble growth and collapse phases in a forward stagnation point flow as a model of reattachment of a boundary layer; a region where severe cavitation damage is often observed. The Kelvin impulse is introduced to aid a better understanding of the mechanics of bubble migration and jet direction in the examples presented. Finally a comparison between the spherical and axisymmetric theories is made for an oscillating bubble in a periodic pressure field; this being of particular interest to current studies in acoustic cavitation and sonoluminescence.

Blake, J. R.; Hooton, M. C.; Robinson, P. B.; Tong, R. P.

110

Experimental analysis of bubble growth, departure and interactions during pool boiling on artificial nucleation sites  

SciTech Connect

The present work describes experimental results of pentane pool boiling, simplified to the cases of boiling on a single or on two adjacent nucleation sites. Bubbles growths have been recorded by a high speed camera under various wall superheat conditions. Bubble volume has been plotted as a function of time, and an experimental growth law has been proposed. Oscillations were observed during growth, showing the interaction of one bubble with the preceding bubble released from the same nucleation site. Lateral coalescence has been visualized and the images have brought to the fore the capillary effects on the distortion of the interface. (author)

Siedel, S.; Cioulachtjian, S.; Bonjour, J. [CETHIL - UMR5008 CNRS INSA-Lyon Univ. Lyon1, Bat. Sadi Carnot, 9 rue de la Physique, INSA-Lyon, F-69621 Villeurbanne Cedex (France)

2008-09-15

111

Sonoluminescence from Stable Cavitation  

Microsoft Academic Search

Arrays of gas bubbles of uniform size are generated in a liquid and subjected to sound at a frequency of 30 kHz. In a viscous mixture of glycerine and water, sonoluminescence is produced in the absence of cavitation noise or streamer activity. Under relatively low amplitude conditions the light occurs in flashes with the same frequency as the sound field,

T. K. Saksena; W. L. Nyborg

1970-01-01

112

Dynamics and energetics of bubble growth in magmas: Analytical formulation and numerical modeling  

Microsoft Academic Search

We have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity, volatile concentration, and diffusivity. On the basis of our formulation we constructed a numerical model of bubble growth

A. A. Proussevitch; D. L. Sahagian

1998-01-01

113

Observations of bubble growth in rhyolite using hot-stage microscopy  

NASA Astrophysics Data System (ADS)

Bubble growth in rhyolitic melts is a primary control on some of the largest explosive eruptions, but growth dynamics remain controversial. We have used hot-stage microscopy to directly observe vesiculation of a Chaiten rhyolite melt (containing ~1.38 wt. % H 2O) at atmospheric pressure. Thin wafers of obsidian were held from 5 minutes up to 2 days in the hot-stage at temperatures between 575 oC and 875 oC. The growth of many individual bubbles was measured using image tracking code within MATLAB. We found that bubble growth rates increased with both temperature and bubble size. The average growth rate at the highest temperature of 875 oC is ~1.27 ?m s-1, compared with the lowest observed growth rate of ~0.02 ?m s-1 at 725 oC; below this temperature no growth was observed. Average growth rate V r follows an exponential relationship with temperature and melt viscosity where V r ~ exp (0.0169T) and V r ~ exp (-1.202?). Comparison of these measured rates with existing bubble growth models (e.g. Navon, Proussevitch and Sahagian) indicates slower growth than expected at the highest temperatures. The extent of diffusive degassing of H 2O and OH- from wafer surfaces during experiments was estimated with simple diffusion models. It was found to be negligible during brief high-temperature experiments but became increasingly important for slower, lower-temperature experiments. Several stages of bubble growth were directly observed, including initial relaxation of deformed existing bubbles into spheres, extensive growth of spheres, and, at higher temperatures, close packing and foam formation. An advantage of the imaging techniques used here is that bubble-bubble interactions can be observed in-situ at relatively high resolution. Bubble deformation due to bubble-bubble interaction and coalescence was observed in most experiments. Evolving bubble number densities (BND) with time were determined, allowing nucleation rates to be estimated. Maximum observed BNDs were 3.4 x 1012 m-3 with maximum increases of around 143 % observed in samples with a lower initial vesicularity <5.7 x 1011 m-3. The experiments described can be used to effectively retrace the vesiculation history of samples, providing a useful tool for aiding in the interpretation of end member products. Figure 1. Nucleation, growth and coalescence of bubbles Summary of findings from vesiculation experiments;

Browning, J.; Tuffen, H.; James, M. R.

2012-12-01

114

Bubble growth rates in nucleate boiling of water at subatmospheric pressures  

Microsoft Academic Search

The growth rate of vapor bubbles is experimentally investigated up to departure in water boiling at pressures ranging from 26.7 to 2.0 kPa. Comparison of the data with existing theory shows the substantial influence of liquid inertia during initial growth and the gradual influence of heat diffusion during advanced growth. The observed bubble growth is found to be in quantitative

S. J. D. van Stralen; W. M. Sluyter; M. S. Sohal; R. Cole

1975-01-01

115

Control of cavitation activity by different shockwave pulsing regimes  

NASA Astrophysics Data System (ADS)

The aim of the study was to control the number of inertial cavitation bubbles in the focal area of an electromagnetic lithotripter in water independently of peak intensity, averaged intensity or pressure waveform. To achieve this, the shockwave pulses were applied in double pulse sequences, which were administered at a fixed pulse repetition frequency (PRF) of 0.33 Hz. The two pulses of a double pulse were separated by a variable short pulse separation time (PST) ranging from 200 µs to 1500 ms. The number and size of the cavitation bubbles were monitored by scattered laser light and stroboscopic photographs. We found that the number of inertial cavitation bubbles as a measure of cavitation dose was substantially influenced by variation of the PST, while the pressure pulse waveform, averaged acoustic intensity and bubble size were kept constant. The second pulse of each double pulse generated more cavitation bubbles than the first. At 14 kV capacitor voltage, the total number of cavitation bubbles generated by the double pulses increased with shorter PST down to approximately 400 µs, the cavitation lifespan. The results can be explained by cavitation nuclei generated by the violently imploding inertial cavitation bubbles. This method of pulse administration and cavitation monitoring could be useful to establish a cavitation dose-effect relationship independently of other acoustic parameters.

Huber, Peter; Debus, Jürgen; Jöchle, Knut; Simiantonakis, Ioannis; Jenne, Jürgen; Rastert, Ralf; Spoo, Julia; Lorenz, Walter J.; Wannenmacher, Michael

1999-06-01

116

Control of cavitation activity by different shockwave pulsing regimes.  

PubMed

The aim of the study was to control the number of inertial cavitation bubbles in the focal area of an electromagnetic lithotripter in water independently of peak intensity, averaged intensity or pressure waveform. To achieve this, the shockwave pulses were applied in double pulse sequences, which were administered at a fixed pulse repetition frequency (PRF) of 0.33 Hz. The two pulses of a double pulse were separated by a variable short pulse separation time (PST) ranging from 200 micros to 1500 ms. The number and size of the cavitation bubbles were monitored by scattered laser light and stroboscopic photographs. We found that the number of inertial cavitation bubbles as a measure of cavitation dose was substantially influenced by variation of the PST, while the pressure pulse waveform, averaged acoustic intensity and bubble size were kept constant. The second pulse of each double pulse generated more cavitation bubbles than the first. At 14 kV capacitor voltage, the total number of cavitation bubbles generated by the double pulses increased with shorter PST down to approximately 400 micros, the cavitation lifespan. The results can be explained by cavitation nuclei generated by the violently imploding inertial cavitation bubbles. This method of pulse administration and cavitation monitoring could be useful to establish a cavitation dose-effect relationship independently of other acoustic parameters. PMID:10498515

Huber, P; Debus, J; Jöchle, K; Simiantonakis, I; Jenne, J; Rastert, R; Spoo, J; Lorenz, W J; Wannenmacher, M

1999-06-01

117

Particle image velocimetry studies of bubble growth and detachment by high-speed photography  

NASA Astrophysics Data System (ADS)

An understanding of bubble flows is important in the design of process equipment, particularly in the chemical and power industries. In vapor-liquid processes the mass and heat transfer between the phases is dominated by the liquid-vapor interface and is determined by the number, size, and shape of the bubbles. For bubble flows these characteristics are often controlled by the generation mechanisms and, since bubble flows are often generated at an orifice, it is important to determine the controlling parameters which dictate how bubbles grow and detach. For bubbles growing at orifices the liquid displacement is an important feature and affects the pressure distribution acting on the bubble and the heat and mass transfer that may occur at the bubble interface. Therefore, in this study, the characteristics of the liquid velocity field are studied experimentally using Particle image Velocimetry (PIV) during growth, detachment and translation of a bubble being generated at an orifice supplied with a constant mass flow rate of air. The process is transient and occurs over a period of approximately 50 msecs. In order to map the transient flow field a combination of high speed cine and cross correlation PIV image processing has been used to determine the liquid velocity vector field during the bubble growth process. The paper contains details of the PIV technique and presents several of the velocity vector maps calculated.

Stickland, Mathew; Dempster, William; Lothian, Lee; Oldroyd, Andrew

1997-05-01

118

A benchmark experiment on gas cavitation  

NASA Astrophysics Data System (ADS)

Cavitation research is often a matter of experiments conducted in complex machinery. There, it is extremely difficult to look into one of the most important issues of cavitation which is nucleation. This work investigates gas cavitation under well-defined flow conditions. Nuclei are placed in wall bound cavities and are exposed to a radial gap flow featuring independent pressure and shear stress. A reciprocating bubble generation is achieved. Bubble frequency and size are evaluated which turn out to depend on pressure and wall shear stress. The experiment lends itself to systematic research in cavitation.

Peters, Franz; Honza, Rene

2014-08-01

119

Cavitation studies in microgravity  

NASA Astrophysics Data System (ADS)

The hydrodynamic cavitation phenomenon is a major source of erosion for many industrial systems such as cryogenic pumps for rocket propulsion, fast ship propellers, hydraulic pipelines and turbines. Erosive processes are associated with liquid jets and shockwaves emission fol-lowing the cavity collapse. Yet, fundamental understanding of these processes requires further cavitation studies inside various geometries of liquid volumes, as the bubble dynamics strongly depends the surrounding pressure field. To this end, microgravity represents a unique platform to produce spherical fluid geometries and remove the hydrostatic pressure gradient induced by gravity. The goal of our first experiment (flown on ESA's parabolic flight campaigns 2005 and 2006) was to study single bubble dynamics inside large spherical water drops (having a radius between 8 and 13 mm) produced in microgravity. The water drops were created by a micro-pump that smoothly expelled the liquid through a custom-designed injector tube. Then, the cavitation bubble was generated through a fast electrical discharge between two electrodes immersed in the liquid from above. High-speed imaging allowed to analyze the implications of isolated finite volumes and spherical free surfaces on bubble evolution, liquid jets formation and shock wave dynamics. Of particular interest are the following results: (A) Bubble lifetimes are shorter than in extended liquid volumes, which could be explain by deriving novel corrective terms to the Rayleigh-Plesset equation. (B) Transient crowds of micro-bubbles (smaller than 1mm) appeared at the instants of shockwaves emission. A comparison between high-speed visualizations and 3D N-particle simulations of a shock front inside a liquid sphere reveals that focus zones within the drop lead to a significantly increased density of induced cavitation. Considering shock wave crossing and focusing may hence prove crucially useful to understand the important process of cavitation erosion. The aim of our future microgravity experiment is to assess the direct effects of gravity on cavitation bubble collapse through a comparison of single cavitation bubbles collapsing in mi-crogravity, normal gravity, and hypergravity. In particular, we shall investigate the shape of the bubble in its final collapse stage and the amount of energy dissipated in the dominant collapse channels, such as liquid jet, shock wave, and rebound bubble. The highly spherical bubbles will be produced via a point-like plasma generated by a high power laser beam. One major hypothesis that we will test is an increase in shock wave energy with decreasing gravity as a consequence of the higher final sphericity and suppression of liquid jets. To support this, we introduce an analytical model for the gravity-perturbed asymmetric collapse of spherical bubbles, and demonstrate that all initially spherical bubbles develop a gravity-related vertical jet along their collapse.

Kobel, Philippe; Obreschkow, Danail; Farhat, Mohamed; Dorsaz, Nicolas; de Bosset, Aurele

120

A New Unsteady Model for Dense Cloud Cavitation in Cryogenic Fluids  

NASA Technical Reports Server (NTRS)

A new unsteady, cavitation model is presented wherein the phase change process (bubble growth/collapse) is coupled to the acoustic field in a cryogenic fluid. It predicts the number density and radius of bubbles in vapor clouds by tracking both the aggregate surface area and volume fraction of the cloud. Hence, formulations for the dynamics of individual bubbles (e.g. Rayleigh-Plesset equation) may be integrated within the macroscopic context of a dense vapor cloud i.e. a cloud that occupies a significant fraction of available volume and contains numerous bubbles. This formulation has been implemented within the CRUNCH CFD, which has a compressible real fluid formulation, a multi-element, unstructured grid framework, and has been validated extensively for liquid rocket turbopump inducers. Detailed unsteady simulations of a cavitating ogive in liquid nitrogen are presented where time-averaged mean cavity pressure and temperature depressions due to cavitation are compared with experimental data. The model also provides the spatial and temporal history of the bubble size distribution in the vapor clouds that are shed, an important physical parameter that is difficult to measure experimentally and is a significant advancement in the modeling of dense cloud cavitation.

Hosangadi, A.; Ahuja, V.

2005-01-01

121

Numerical study of bubble growth and wall heat transfer during flow boiling in a microchannel  

E-print Network

Numerical study of bubble growth and wall heat transfer during flow boiling in a microchannel A 2011 Accepted 27 January 2011 Available online 12 April 2011 Keywords: Flow boiling Microchannels saturation temperature. During flow boiling, bubbles nucleate on the microchannel walls and may grow big en

Kandlikar, Satish

122

Cavitation inside high-speed liquid droplet impacting on the solid surface  

NASA Astrophysics Data System (ADS)

The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the solid surface are investigated numerically, using Ghost Fluid Method with TVD-ENO-LLF to solve pressure propagation in two phase compressible flow. Upon the impact on the surface, strong compression wave is generated on the contact surface inside liquid droplet. This wave propagates upward to the free surface and is reflected normal to the surface as an expansion wave, which propagates downward. This expansion wave focuses inside liquid droplet, which results in the generation of low pressure region. We discuss the condition of cavitation bubble growth in this low pressure region, with the effects of thermal environment of liquid droplet taken into account. We evaluate the magnitude of the attainable pressure during bubble collapse, by solving equation of radial motion of single bubble with ambient pressure change, and compare this bubble collapsing pressure to the high-speed liquid droplet impact pressure in order to discuss the contribution of cavitation bubble to the erosion of solid surface.

Watanabe, Masao; Sanada, Toshiyuki; Yamase, Masao

2007-11-01

123

Experimental growth law for bubbles in a "wet" 3D liquid foam  

E-print Network

We used X-ray tomography to characterize the geometry of all bubbles in a liquid foam of average liquid fraction $\\phi_l\\approx 17 %$ and to follow their evolution, measuring the normalized growth rate $\\mathcal{G}=V^{-{1/3}}\\frac{dV} {dt}$ for 7000 bubbles. While $\\mathcal{G}$ does not depend only on the number of faces of a bubble, its average over $f-$faced bubbles scales as $G_f\\sim f-f_0$ for large $f$s at all times. We discuss the dispersion of $\\mathcal{G}$ and the influence of $V$ on $\\mathcal{G}$.

Jérôme Lambert; Rajmund Mokso; Isabelle Cantat; Peter Cloetens; Renaud Delannay; James A. Glazier; François Graner

2007-02-28

124

Cavitation and Superplasticity.  

National Technical Information Service (NTIS)

Cavitation occurs in many alloy systems during superplastic flow. Cavities either pre-exist or nucleate on grain boundaries and their subsequent growth, coalescence, and interlinkage leads to premature failure. The presence of cavities in superplastically...

N. Ridley

1989-01-01

125

Analysis of quasi-static vapour bubble shape during growth and departure  

NASA Astrophysics Data System (ADS)

In an effort to better understand the physical mechanisms responsible for pool boiling heat transfer, a numerical solution to the capillary equation is used to describe bubble shape evolution. Indeed, any analysis of thermal transport due to nucleate pool boiling requires bubble frequency and volume predictions, which are intimately linked to bubble shape. To this end, a numerical treatment of the capillary equation is benchmarked to profiles measured from captured images of vapour bubble formations. The bubble growth is quasi-static in a quiescent liquid with a triple contact line fixed to the perimeter of a needle orifice. This investigation provides insight into the dependence the bubble shape evolution has on the physical mechanisms quantified in the Bond number with characteristic length equal to the cavity radius.

Lesage, Frédéric J.; Cotton, James S.; Robinson, Anthony J.

2013-06-01

126

Dynamics of bubble growth on a heated surface under low gravity conditions  

NASA Astrophysics Data System (ADS)

Experimental studies and numerical simulations of the single bubble growth and departure mechanisms under low gravity have been conducted. An artificial cavity of 10 ?m in diameter was made on the polished Silicon wafer. The back surface of the wafer was electrically heated in order to control the surface nucleation superheat. The experiments were performed during the parabola flights of the KC-135. The test liquid was degassed water in the pressure range 14.7-18.0 Psia. The data of bubble size and shape from nucleation to departure as well as bubble growth time were obtained for wall superheats between 2.5 and 6.5 °C under saturation and small subcooling conditions. Analytical/numerical models were developed to describe the heat transfer through the micro-macro layer underneath and around a bubble formed at a nucleation site. In the micro layer model the capillary and disjoining pressures were included. Evolution of the bubble-liquid interface along with induced liquid motion was modeled. The experimental data and the computational prediction showed a good agreement. From the comparison of the low gravity results and those at earth normal gravity it is found that at the same wall superheat and liquid subcooling the bubble departure diameter can be approximately related to the gravity level through the relation Dd~1/g. Liquid subcooling has an appreciable effect on the bubble growth period. A relatively small subcooling can significantly prolong the time a bubble stays on the heater surface. .

Qiu, D. M.; Singh, S.; Dhir, V. K.

2000-01-01

127

RANTES and fibroblast growth factor 2 in jawbone cavitations: triggers for systemic disease?  

PubMed Central

Background Jawbone cavitations (JC) are hollow dead spaces in jawbones with dying or dead bone marrow. These areas are defined as fatty degenerative osteonecrosis of the jawbone or neuralgia-inducing cavitational osteonecrosis and may produce facial pain. These afflictions have been linked to the immune system and chronic illnesses. Surgical debridement of JC is reported to lead to an improvement in immunological complaints, such as rheumatic, allergic, and other inflammatory diseases (ID). Little is known about the underlying cause/effect relationship. Objectives JC bone samples were analyzed to assess the expression and quantification of immune modulators that can play a role in the pathogenesis of IDs. The study supports a potential mechanism where JC is a mediating link in IDs. Materials and methods Samples of fatty softened bone taken from JCs were extracted from 31 patients. The specimens were analyzed by bead-based multiplex technology and tested for seven immune messengers. Results Regulated upon activation, normal T-cell expressed, and secreted (RANTES) and fibroblast growth factor (FGF)-2 were found at high levels in the JCs tested. Other cytokines could not be detected at excessive levels. Discussion The study confirms that JC is able to produce inflammatory messengers, primarily RANTES, and, secondarily, FGF-2. Both are implicated in many serious illnesses. The excessive levels of RANTES/FGF-2 in JC patients with amyotrophic lateral sclerosis, multiple sclerosis, rheumatoid arthritis, and breast cancer are compared to levels published in medical journals. Levels detected in JCs are higher than in the serum and cerebrospinal fluid of amyotrophic lateral sclerosis and multiple sclerosis patients and four-fold higher than in breast cancer tissue. Conclusion This study suggests that JC might serve as a fundamental cause of IDs, through RANTES/FGF-2 production. Thus, JC and implicated immune messengers represent an integrative aspect of IDs and serve as a possible cause. Removing JCs may be a key to reversing IDs. There is a need to raise awareness about JC throughout medicine and dentistry. PMID:23637551

Lechner, Johann; von Baehr, Volker

2013-01-01

128

Study of bubble growth in water pool boiling through synchronized, infrared thermometry and high-speed video  

E-print Network

High-speed video and infrared thermometry were used to obtain time- and space-resolved information on bubble nucleation and heat transfer in pool boiling of water. The bubble departure diameter and frequency, growth and ...

Gerardi, Craig

129

An experimental investigation of bubble growth and detachment in vertical upflow and downflow boiling  

Microsoft Academic Search

A visual study of vapor bubble growth and departure in vertical upflow and downflow forced convection boiling is presented. A vertical flow boiling facility was constructed with a transparent, electrically-heated test section in which the ebullition process could be observed. High-speed digital images of flow boiling phenomena were obtained, which were used to measure bubble growth, departure diameters, and lift-off

G. E. Thorncroft; J. F. Klausner; R. Mei

1998-01-01

130

The dissolution or growth of a gas bubble inside a drop in zero gravity  

NASA Technical Reports Server (NTRS)

The radius-time history of a gas bubble located concentrically within a spherical liquid drop in a space laboratory is analyzed within the framework of the quasi-stationary approximation. Illustrative results are calculated from the theory which demonstrate interesting qualitative features. For instance, when a pure gas bubble dissolves within a liquid drop in an environment containing the same gas and some inert species, the dissolution can be more or less rapid than that in an unbounded liquid depending on the initial relative size of the drop. Further, given a similar growth situation, indefinite growth is not possible, and the bubble will initially grow, but always dissolve in the end.

Kondos, Pericles A.; Subramanian, R. Shankar; Weinberg, Michael C.

1987-01-01

131

Deformed bubble growth and coalescence in polymer foam processing  

E-print Network

the geometrical constraints imposed by the existence of neighboring growing bubbles. The viscoelastic behavior of the polymer melt as well as the effect of the intermolecular forces on foam stability are investigated. An analysis of the results indicates...

Allaboun, Hussein Raji

2012-06-07

132

Evaporation-induced cavitation in nanofluidic channels  

E-print Network

Cavitation, known as the formation of vapor bubbles when liquids are under tension, is of great interest both in condensed matter science as well as in diverse applications such as botany, hydraulic engineering, and medicine. ...

Karnik, Rohit N.

133

Acoustic cavitation and its chemical consequences  

E-print Network

results in an enormous concentration of energy from the conversion of the kinetic energy of liquid motionAcoustic cavitation and its chemical consequences By Kenneth S. Suslick, Yuri Didenko, Ming M. Fang Acoustic cavitation is responsible for both sonochemistry and sonoluminescence. Bubble collapse in liquids

Suslick, Kenneth S.

134

Effects of microgravity on Marangoni convection and growth characteristic of a single bubble  

NASA Astrophysics Data System (ADS)

Based on previous experiments and the volume of fluid (VOF) multiphase model, the growth characteristics of a single bubble have been numerically investigated in a rectangular pool (10×10×25 mm3) under microgravity. The transport of mass and energy during phase change was realized by source terms of the mass and energy equations through user-defined functions (UDF). Under microgravity, the results show that the temperature and the streamline field distribution around the bubble are significantly changed as compared to the ones of terrestrial conditions. The temperature profile at the two-phase interface is no longer a uniform distribution, and the Marangoni flows are more obvious at the two-phase interface. The effects of gravity on the detachment of the bubble are significant: the bubble does not immediately detach from the heating wall under microgravity conditions. The surface tension gradient caused by the Marangoni effect is more significant at lower microgravity. Bubble growth is more complex under microgravity conditions than normal gravity conditions, and it is related to the magnitude of the microgravity: the lower the microgravity, the higher the bubble growth rate. Furthermore, under microgravity, the bubble diameter changes differently, and the fluctuation amplitude of the heat transfer coefficient increases with increasing microgravity.

Yang, Yan; Pan, Liang-ming; Xu, Jian-jun

2014-07-01

135

Pressure and noise induced by a cavitating marine screw propeller  

NASA Astrophysics Data System (ADS)

A method of evaluating the intermittent propeller blade fixed cavitation and shedding of free cavitation bubbles is presented. The number and size of free cavitation bubbles are related to the variation of propeller blade attached cavitation. The beta type probability density distribution of the initial bubble size is proposed. This distribution is normalized with respect to the sheet cavitation thickness. The effect of the simplications in the dynamic model of the cavitation bubbles on their collapse downstream of partially and fully cavitating hydrofoils is discussed. The method of calculating the low frequency pressures induced by fixed blade cavitation and high frequency broadband noise caused by the collapse of free bubbles in propeller flows is presented. The method yields noise spectra in the frequency range from the blade passing frequency to tens of kiloHertz. Computed pressure and noise induced by the cavitating propellers are compared to the values measured in model and full scale experiments. The fractal structure of the bubble cloud and the proposed method of evaluating the collapse of the bubble cloud downstream of the fixed cavities yield noise spectra which correlate well with the experimental results of full and model scale measurements.

Matusiak, Jerzy

1992-01-01

136

Taxing the rich: recombinations and bubble growth during reionization  

NASA Astrophysics Data System (ADS)

Reionization is inhomogeneous for two reasons: the clumpiness of the intergalactic medium (IGM), and clustering of the discrete ionizing sources. While numerical simulations can in principle take both into account, they are at present limited by small box sizes. On the other hand, analytic models have only examined the limiting cases of a clumpy IGM (with uniform ionizing emissivity) and clustered sources (embedded in a uniform IGM). Here, we present the first analytic model that includes both factors. At first, recombinations can be ignored and ionized bubbles grow primarily through major mergers, because at any given moment the bubbles have a well-defined characteristic size. As a result, reionization resembles `punctuated equilibrium,' with a series of well-separated sharp jumps in the ionizing background. These features are local effects and do not reflect similar jumps in the global ionized fraction. We then combine our bubble model with a simple description of recombinations in the IGM. We show that the bubbles grow until recombinations balance ionizations, when their expansion abruptly halts. If the IGM density structure is similar to that at moderate redshifts, this limits the bubble radii to ~20 comoving Mpc; however, if the IGM is significantly clumpier at higher redshifts (because of minihalo formation, for example), the limit could be much smaller. Once a bubble reaches saturation, that region of the Universe has for all intents and purposes entered the `post-overlap' stage. Because different HII regions saturate over a finite time interval, the overlap epoch actually has a finite width. Our model also predicts a mean recombination rate several times larger than expected for a uniformly illuminated IGM. This picture naturally explains the substantial large-scale variation in Lyman-series opacity along the lines of sight to the known z > 6 quasars. More quasar spectra will shed light on the transition between the `bubble-dominated' topology characteristic of reionization and the `web-dominated' topology characteristic of the later Universe.

Furlanetto, Steven R.; Oh, S. Peng

2005-11-01

137

Taxing the Rich: Recombinations and Bubble Growth During Reionization  

E-print Network

Reionization is inhomogeneous for two reasons: the clumpiness of the intergalactic medium (IGM) and clustering of the discrete ionizing sources. While numerical simulations can in principle take both into account, they are at present limited by small box sizes. On the other hand, analytic models have only examined the limiting cases of a clumpy IGM (with uniform ionizing emissivity) and clustered sources (embedded in a uniform IGM). Here, we present an analytic model for the evolving topology of reionization that includes both factors. At first, recombinations can be ignored and ionized bubbles grow primarily through major mergers. As a result, reionization resembles "punctuated equilibrium," with a series of well-separated sharp jumps in the ionizing background. These features are local effects and do not reflect similar jumps in the global ionized fraction. We then combine our bubble model with a simple description of recombinations in the IGM. We show that the bubbles stop growing when recombinations balan...

Furlanetto, S R; Furlanetto, Steven R.

2005-01-01

138

Taxing the Rich: Recombinations and Bubble Growth During Reionization  

E-print Network

Reionization is inhomogeneous for two reasons: the clumpiness of the intergalactic medium (IGM) and clustering of the discrete ionizing sources. While numerical simulations can in principle take both into account, they are at present limited by small box sizes. On the other hand, analytic models have only examined the limiting cases of a clumpy IGM (with uniform ionizing emissivity) and clustered sources (embedded in a uniform IGM). Here, we present an analytic model for the evolving topology of reionization that includes both factors. At first, recombinations can be ignored and ionized bubbles grow primarily through major mergers. As a result, reionization resembles "punctuated equilibrium," with a series of well-separated sharp jumps in the ionizing background. These features are local effects and do not reflect similar jumps in the global ionized fraction. We then combine our bubble model with a simple description of recombinations in the IGM. We show that the bubbles stop growing when recombinations balance ionizations. If the IGM density structure is similar to that at moderate redshifts, this limits the bubble radii to ~20 comoving Mpc; however, it may be much smaller if the IGM is significantly clumpier at higher redshifts. Once a bubble reaches saturation, that region of the universe has for all intents and purposes entered the "post-overlap" stage, so the overlap epoch actually has a finite width. This picture naturally explains the substantial large-scale variation in Lyman-series opacity along the lines of sight to the known z>6 quasars. More quasar spectra will shed light on the transition between the "bubble-dominated" topology characteristic of reionization and the "web-dominated" topology characteristic of the later universe. [Abridged

Steven R. Furlanetto; S. Peng Oh

2005-05-03

139

Interaction of two differently sized oscillating bubbles in a free field  

E-print Network

Most real life bubble dynamics applications involve multiple bubbles, for example, in cavitation erosion prevention, ultrasonic baths, underwater warfare, and medical applications involving microbubble contrast agents. ...

Chew, Lup Wai

140

Bubble Proliferation in Shock Wave Lithotripsy Occurs during Inertial Collapse  

NASA Astrophysics Data System (ADS)

In shock wave lithotripsy (SWL), firing shock pulses at slow pulse repetition frequency (0.5 Hz) is more effective at breaking kidney stones than firing shock waves (SWs) at fast rate (2 Hz). Since at fast rate the number of cavitation bubbles increases, it appears that bubble proliferation reduces the efficiency of SWL. The goal of this work was to determine the basis for bubble proliferation when SWs are delivered at fast rate. Bubbles were studied using a high-speed camera (Imacon 200). Experiments were conducted in a test tank filled with nondegassed tap water at room temperature. Acoustic pulses were generated with an electromagnetic lithotripter (DoLi-50). In the focus of the lithotripter the pulses consisted of a ˜60 MPa positive-pressure spike followed by up to -8 MPa negative-pressure tail, all with a total duration of about 7 ?s. Nonlinear propagation steepened the shock front of the pulses to become sufficiently thin (˜0.03 ?m) to impose differential pressure across even microscopic bubbles. High-speed camera movies showed that the SWs forced preexisting microbubbles to collapse, jet, and break up into daughter bubbles, which then grew rapidly under the negative-pressure phase of the pulse, but later coalesced to re-form a single bubble. Subsequent bubble growth was followed by inertial collapse and, usually, rebound. Most, if not all, cavitation bubbles emitted micro-jets during their first inertial collapse and re-growth. After jetting, these rebounding bubbles could regain a spherical shape before undergoing a second inertial collapse. However, either upon this second inertial collapse, or sometimes upon the first inertial collapse, the rebounding bubble emerged from the collapse as a cloud of smaller bubbles rather than a single bubble. These daughter bubbles could continue to rebound and collapse for a few cycles, but did not coalesce. These observations show that the positive-pressure phase of SWs fragments preexisting bubbles but this initial fragmentation does not yield bubble proliferation, as the daughter bubbles coalesce to reform a single bubble. Instead, bubble proliferation is the product of the subsequent inertial collapses.

Pishchalnikov, Yuri A.; McAteer, James A.; Pishchalnikova, Irina V.; Williams, James C.; Bailey, Michael R.; Sapozhnikov, Oleg A.

2008-06-01

141

Nucleation and Growth of Bubbles in He Ion Implanted V/Ag Multilayers,  

SciTech Connect

Microstructures of He ion-implanted pure Ag, pure V and polycrystalline V/Ag multilayers with individual layer thickness ranging from 1?nm to 50?nm were investigated by transmission electron microscopy (TEM). The bubbles in the Ag layer were faceted and larger than the non-faceted bubbles in the V layer under the same implantation conditions for both pure metals and multilayers. The substantially higher single defects surviving the spike phase and lower mobility of trapped He in bcc than those in fcc could account for this difference. For multilayers, the bubbles nucleate at interfaces but grow preferentially in Ag layers due to high mobility of trapped He in fcc Ag. In addition, the He concentration above which bubbles can be detected in defocused TEM images increases with decreasing layer thickness, from 0 for pure Ag to 4–5 at. % for 1?nm V/1?nm Ag multilayers. In contrast, the bubble size decreases with decreasing layer thickness, from approximately 4?nm in diameter in pure Ag to 1?nm in the 1?nm V/1?nm Ag multilayers. Elongated bubbles confined in the Ag layer by the V–Ag interfaces were observed in 1?nm multilayers. These observations show that bubble nucleation and growth can be suppressed to high He concentrations in nanoscale composites with interfaces that have high He solubility.

Wei, Q. M.; Wang, Y. Q.; Nastasi, Michael; Misra, A.

2011-01-01

142

MTBE degradation by hydrodynamic induced cavitation.  

PubMed

Hydrodynamic induced cavitation generates imploding cavitation bubbles which can lead to degradation or even mineralisation of water constituents without addition of any chemicals. This technology overcomes the problems of ultrasound irradiation by the local production of a cavitation cloud close to the sonotrodes. Hydrodynamic cavitation can be stabilised downstream of the nozzle depending on the ambient pressure conditions. If the pressure is kept low, the imploding cavitation bubbles generate new cavities, analogous to a chain reaction, and elevate the radical synthesis inside the apparatus. During the pilot tests MTBE and ETBE were degraded and complete mineralisation started at a time delay of app. 30 min. The specific energy demand for MTBE degradation lies in the range of app. 200 Wh/ppm in the investigated concentration range of about 30 ppm. PMID:20453332

Schmid, A

2010-01-01

143

Computational Study of Adiabatic Bubble Growth Dynamics from Submerged Orifices in Aqueous Solutions of Surfactants  

NASA Astrophysics Data System (ADS)

The growth dynamics of isolated gas bubbles (inception ? growth ? departure) emanating from a capillary-tube orifice submerged in isothermal pools of aqueous solutions of surfactants is computationally investigated. The Navier-Stokes equations are solved in the liquid and the gas phase. The evolution of the gas-liquid interface is tracked using a Volume-of-Fluid (VOF) method. Surfactant molecules in aqueous solutions have a tendency to diffuse towards the gas-liquid interface and are subsequently adsorbed onto it. This time dependent adsorption process gives rise to the dynamic surface tension behavior of the aqueous surfactant solutions. To computationally model this behavior, the species conservation equation for the surfactant is solved in the bulk fluid and is coupled with the dynamic adsorption-desorption of the surfactant on the interface. A new form of the surfactant transport equation is derived that was necessary to incorporate the interfacial transport in the volume-of-fluid method where the interface is spread over multiple grid cells. Computational results were obtained for bubble growth dynamics from a capillary orifice in a pool of pure water and in an aqueous solution of Sodium Dodecyl Sulphate (SDS). The evolving bubble shape and the flow field in the two phases in the pure liquid and in surfactant solution are compared for a variety of air flow rates (from 4 ml/min to 24 ml/min) in the constant bubble regime. To validate the computational model, the results for the transient shape and size of growing bubbles in pure water were compared with available experimental data and were found to be in excellent agreement. Results show that the dynamic surface tension relaxation gives rise to smaller bubble size at departure in aqueous surfactant solution compared to that in pure water. However, this effect is found to be a function of the air flow rate. At high air flow rates (24 ml/min), the short time for bubble growth allows relatively smaller drop in the surface tension and produces departure diameters similar to bubble diameters in water. At low air flow rates (4 ml/min), the departure time is much larger and allows for complete surface tension relaxation. As such the departure diameters at low air flow rates in aqueous surfactant solution are significantly smaller than those predicted in pure water. Also, the flow patterns around a growing bubble in surfactant solution are altered due to the non-uniform surfactant adsorption along the gas-liquid interface. The computational results elucidate the role of surfactant transport on bubble growth dynamics.

Deodhar, Anirudh M.

144

CAVITATION DAMAGE STUDY VIA A NOVEL REPETITIVE PRESSURE PULSE APPROACH  

SciTech Connect

Cavitation damage can significantly affect system performance. Thus, there is great interest in characterizing cavitation damage and improving materials resistance to cavitation damage. In this paper, we present a novel methodology to simulate cavitation environment. A pulsed laser is utilized to induce optical breakdown in the cavitation media, with the emission of shock wave and the generation of bubbles. The pressure waves induced by the optical breakdown fluctuate/propagate within the media, which enables the cavitation to occur and to further develop cavitation damage at the solid boundary. Using the repetitive pulsed-pressure apparatus developed in the current study, cavitation damage in water media was verified on stainless steel and aluminum samples. Characteristic cavitation damages such as pitting and indentation are observed on sample surfaces using scanning electron microscopy.

Wang, Jy-An John [ORNL; Ren, Fei [ORNL; Wang, Hong [ORNL

2010-01-01

145

A four-dimensional X-ray tomographic microscopy study of bubble growth in basaltic foam.  

PubMed

Understanding the influence of bubble foams on magma permeability and strength is critical to investigations of volcanic eruption mechanisms. Increasing foam porosity decreases strength, enhancing the probability of an eruption. However, higher porosities lead to larger permeabilities, which can lessen the eruption hazard. Here we measure bubble size and wall thickness distributions, as well as connectivity, and calculate permeabilities and tensile strengths of basaltic foams imaged by synchrotron X-ray tomographic microscopy during bubble growth in hydrated basaltic melts. Rapid vesiculation produces porous foams whose fragmentation thresholds are only 5-6?MPa and whose permeabilities increase from approximately 1×10(-10) to 1×10(-9)?m(2) between 10 and 14?s despite decreasing connectivity between bubbles. These results indicate that basaltic magmas are most susceptible to failure immediately upon vesiculation and at later times, perhaps only 10's of seconds later, permeability increases may lessen the hazard of explosive, basaltic, Plinian eruptions. PMID:23072805

Baker, Don R; Brun, Francesco; O'Shaughnessy, Cedrick; Mancini, Lucia; Fife, Julie L; Rivers, Mark

2012-01-01

146

Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation  

NASA Technical Reports Server (NTRS)

The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets appear inside the gas mixture due to a uniform nucleation and the temperature recovers, thus the motion of the bubble is apparently isothermal; (2) the evaporation and condensation coefficient largely affects bubble motions (maximum radius, period and rate of attenuation of the bubble oscillation) including the uniform contraction; (3) the oscillation period of the bubble is longer as the equilibrium bubble radius is larger when the surrounding pressure decreases stepwise. In this circumstance the temperature inside the bubble is kept constant due to condensation evaporation phenomena and is nearly isothermal; and (4) when the surrounding pressure decreases in a stepwise fashion, the critical pressure bubble radius relation becomes closer to that for the isothermal process if the bubble radius is larger than 8 microns.

Matsumoto, Y.

1988-01-01

147

hal-00134104,version1-28Feb2007 Experimental growth law for bubbles in a "wet" 3D liquid foam  

E-print Network

hal-00134104,version1-28Feb2007 Experimental growth law for bubbles in a "wet" 3D liquid foam J their evolution, measuring the normalized growth rate G = V - 1 3 dV dt for 7000 bubbles. While G does not depend occupying a fraction l of the foam's volume. Liquid foams coarsen because gas slowly diffuses through

Paris-Sud XI, Université de

148

Cavitation inside high-speed liquid droplet impacting on the solid surface  

Microsoft Academic Search

The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the solid surface are investigated numerically, using Ghost Fluid Method with TVD-ENO-LLF to solve pressure propagation in two phase compressible flow. Upon the impact on the surface, strong compression wave is generated on the contact surface inside liquid droplet. This wave propagates upward to the free

Masao Watanabe; Toshiyuki Sanada; Masao Yamase

2007-01-01

149

Frequency-sum passive cavitation imaging.  

PubMed

Passive cavitation imaging (PCI) is a method for spatially mapping acoustic emissions caused by microbubble activity, including subharmonic and ultraharmonic emissions that denote stable cavitation. The point spread function (PSF) of passive cavitation images is diffraction limited. When typical clinical diagnostic linear arrays are used for PCI, the diffraction limit results in high azimuthal resolution but low axial resolution. Abadi et al. (2013)recently demonstrated a method called frequency-sum beamforming, which employs second-order or higher products of the acoustic emissions to manufacture higher frequencies, thereby reducing the size of the PSF. We applied this approach to cavitation emissions recorded from albumin-shelled bubbles insonified by 2 MHz ultrasound. Cavitation emissions were recorded on a 5 MHz, 128 element linear array using a Vantage scanner (Verasonics Inc.). Quadratic and fourth-order frequency-sum beamforming was applied to both harmonic and ultraharmonic cavitation emissions. Corresponding simulations were also performed to illustrate frequency-sum passive cavitation imaging of multiple bubbles. In comparison to delay-and-sum PCI, apparent areas of cavitation activity decreased when products of the emissions were used to perform frequency-sum beamforming. However, frequency-sum beamforming also produced artifacts, including the appearance of spurious emission sources. PMID:25235673

Haworth, Kevin J; Radhakrishnan, Kirthi; Mast, T Douglas

2014-04-01

150

Numerical simulation of aeration bubble growth in a plug-flow aeration tank used in wastewater treatment  

NASA Astrophysics Data System (ADS)

The micro-scale hydrodynamics of bubbles growth by aeration is related to the oxygen transfer efficiency and the overall performance of the activated sludge wastewater treatment process. To gain a deeper insight on the micro-scale phenomena of dispersed bubble in this process, a three-dimensional direct simulation method is developed to study the effects of the liquid cross-flow on micro-scale behavior of bubble growth in a plug-flow aeration tank. The numerical simulations are performed using the level set method coupling with the governing equations of a single fluid with variable properties. The governing equations are solved using the finite-volume projection technique. The simulation results are compared with the experimental observations and theoretical relations. The simulated results show that water cross-flow in plug-flow type aeration tank has a strong impact on the bubble growth process. Compared to that generated under quiescent water conditions used in mixing type aeration tank, the bubble under water cross-flow conditions grows downstream along the tilted axis, and the bubble generation time tends to decrease noticeably and the bubble at detachment has significantly smaller size. The dynamic characteristics of the bubble growth through two orifices are also numerically studied. The effect of water cross-flow on the bubbling synchronicity is finally discussed.

Wang, H. R.; Li, Y. P.

2010-03-01

151

Bacterial Sterilization Using Cavitating Jet  

NASA Astrophysics Data System (ADS)

In this paper, a new sterilization method using cavitating flow is presented. Water with bacteria was pressurized up to 105 MPa and flushed out through two very small nozzles 0.1-0.31 mm in diameter, where a cavitating jet was generated containing bubbles that collapsed downstream. First, the effects of jet velocity and cavitation number on the sterilization rate of Escherichia coli JCM1649T (E. coli) were examined. The sterilization rate increased with jet velocity. The rate was proportional to the 3rd power of the velocity. All the E. coli cells were killed by three successive treatments at V=355.7 m/s and cavitation number ?=0.154. The sterilization rate has a peak depending on cavitation number at the low-jet-velocity region of less than 300 m/s. An experiment was also performed to compare two types of bacteria, E. coli, as typical Gram-negative bacteria and Bacillus subtilis JCM1465T (B. subtilis), as typical Gram-positive bacteria. Additional tests were performed using Pseudomonas putida JCM13063T, Gram-negative bacteria and Bacillus halodurans JCTM9153, Gram-positive bacteria. The sterilization rate of the Gram-positive bacteria was much lower than that of the Gram-negative bacteria under the same experimental conditions. Gram-positive bacteria have a thicker peptidoglycan layer than Gram-negative bacteria. This may be the reason why B. subtilis is more resistant to the mechanical stress caused by cavitating flow.

Azuma, Yohei; Kato, Hiroharu; Usami, Ron; Fukushima, Tadamasa

152

Cavitation in elastomeric solids: II--Onset-of-cavitation surfaces for Neo-Hookean materials  

E-print Network

Cavitation in elastomeric solids: II--Onset-of-cavitation surfaces for Neo-Hookean materials Oscar-existing defects. In this article, the theory is used to determine onset-of-cavitation surfaces for Neo simulations for the growth of a small spherical cavity in a Neo-Hookean block under multi-axial loading. Good

Lopez-Pamies, Oscar

153

Experimental and Theoretical Investigations of Cavitation in Water  

NASA Technical Reports Server (NTRS)

The cavitation in nozzles on airfoils of various shape and on a sphere are experimentally investigated. The limits of cavitation and the extension of the zone of the bubbles in different stages of cavitation are photographically established. The pressure in the bubble area is constant and very low, jumping to high values at the end of the area. The analogy with the gas compression shock is adduced and discussed. The collapse of the bubbles under compression shock produces very high pressures internally, which must be contributory factors to corrosion. The pressure required for purely mechanical corrosion is also discussed.

Ackeret, J.

1945-01-01

154

Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO2  

SciTech Connect

Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas bubbles at grain boundaries for given grain boundary properties. More validation of the model capability in polycrystalline is underway.

Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

2012-05-30

155

NUMERICAL ANALYSIS OF VAPOR BUBBLE GROWTH AND WALL HEAT TRANSFER DURING FLOW BOILING OF WATER IN A MICROCHANNEL  

E-print Network

NUMERICAL ANALYSIS OF VAPOR BUBBLE GROWTH AND WALL HEAT TRANSFER DURING FLOW BOILING OF WATER in various applications such as electronic chip cooling. At sufficiently high wall superheats, flow boiling boiling, bubbles nucleate on the microchannel walls and eventually grow big enough to fill up the entire

Kandlikar, Satish

156

The dynamics of a vapour bubble growth under the boiling of a subcooled liquid in low volumes  

NASA Astrophysics Data System (ADS)

This paper presents an experimental study of the dynamics of a vapour bubble growth under the boiling of a subcooled liquid in low volumes. The influence of the mode parameters (heat flux and subcooling to the saturation temperature) on the geometric characteristics of the vapour bubble (base diameter and height) has been found.

Orlova, Evgenija; Kuznetsova, Geniy; Feoktistovb, Dmitriy

2014-08-01

157

Dissolved water distribution in vesicular magmatic glass records both decompressive bubble growth and quench resorption  

NASA Astrophysics Data System (ADS)

Water distribution in magma varies over the lifetime of an eruption due to a variety of processes, including decompressive degassing of the melt, cooling during the quench from melt to glass, and post-emplacement hydration under ambient conditions. Correct interpretation of water distributions in erupted pyroclasts can therefore offer crucial insights into the dynamics of eruption mechanisms and emplacement histories. Volcanic eruptions are driven by the nucleation and growth of bubbles in magma. Bubbles grow as volatile species in the melt, of which water is volumetrically the most important, diffuse down a concentration gradient towards and across the bubble wall. On cooling, the melt quenches to glass, preserving the spatial distribution of water concentration around the bubbles (now vesicles). We use Backscatter Scanning Electron Microscopy (BSEM), Secondary Ion Mass Spectrometry (SIMS) and Fourier Transform Infra-Red spectroscopy (FTIR) to measure the spatial distribution of water around vesicles in experimentally-vesiculated samples. We find that, contrary to expectation, the total water concentration increases (by up to 2 wt.%) in the ~30 microns closest to the vesicle wall. Our samples record significant resorption of water back into the melt around bubbles during the quench process, a process which represents ';regassing' of the magma. We propose that the observed total water resorption profiles result from the increase in the equilibrium solubility of water as temperature decreases during the quench to glass, and that this resorption locally overprints the pre-existing concentration total water profile resulting from bubble growth during decompression. This resorption occurs over the very short timescales of rapid experimental quench (3-10 seconds) resulting in strongly disequilibrium water speciation. Water re-enters the melt as molecular water leading to enrichment in molecular water around vesicles, while the distribution of hydroxyl groups remains relatively unaltered during quench, thus preserving information about syn-experimental (or syn-eruptive) degassing. Our work demonstrates the effectiveness of two tools for deciphering the water contents of pyroclasts. BSEM imaging of glassy pyroclasts offers an easy, qualitative assessment of whether glass has been affected by quench resorption or secondary alteration processes, which becomes quantitative if calibrated by a technique such as SIMS. FTIR speciation data, meanwhile, enables the cause of bubble resorption to be identified, since resorption caused by pressure increase and by temperature decrease will result in distinctly different distributions of water species. We present here data extracted using these tools that demonstrate the potential impact of temperature-controlled quench resorption, which can reduce bubble volumes and sample porosities by a factor of two and reintroduce significant amounts of water back into the melt, with implications for obsidian and rheomorphic flow mechanisms.

McIntosh, I. M.; Llewellin, E.; Humphreys, M.; Nichols, A. R.; Burgisser, A.; Schipper, C.

2013-12-01

158

High-speed Observation of Two-frequency Controlled Cloud Cavitation in HIFU Field  

Microsoft Academic Search

Ultrasound induced cavitation control with application to lithotripsy has been investigated. Previously, a two-frequency ultrasound combination has been proposed to utilize the violent collapse of the cloud cavitation. In this paper, the cavitation cloud collapse phenomena is investigated experimentally in more detail. The behaviour of the bubble cloud formation in the high frequency phase (3.88 [MHz]) is photographed. Then low

Teiichiro Ikeda; Masataka Tosaki; Shin Yoshizawa; Yoichiro Matsumoto

2005-01-01

159

E. M. Agrest and G. N. Kuznetsov THE ORIGINATION AND DEVELOPMENT OF ULTRASONIC CAVITATION ON  

Microsoft Academic Search

An analysis of cavitation nucleus (gas bubbles in sound fields, generated by various forms oscillators) dynamics is presented. Some general regularity caused by interactions of cavitation nucleus with inhomogeneous sound fields with alternative pressure gradients are stated. It is concluded that the main mechanism of the inception of the earlier stage of cavitation is caused by Bierkness and pressure gradient

VARIOUS FORM OSCILLATORS

2003-01-01

160

Numerical simulation of growth of a vapor bubble during flow boiling of water in a microchannel  

Microsoft Academic Search

The present study is performed to numerically analyze the growth of a vapor bubble during flow of water through a microchannel. The complete Navier–Stokes equations, along with continuity and energy equations, are solved using the SIMPLER (semi-implicit method for pressure-linked equations revised) method. The liquid–vapor interface is captured using the level set technique. The microchannel is 200-µm square in cross-section

Abhijit Mukherjee; Satish G. Kandlikar

2005-01-01

161

Chemical Applications of Electrohydraulic Cavitation for Hazardous Waste Control  

E-print Network

CHEMICAL APPLICATIONS OF ELECTROHVDRAULIC CAVITATION FOR HAZARDOUS WASTE CONTROL MICHAEL R. HOFFMANN, PROFESSOR, CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CA 91125 Abstract We have been investigating the fundamental chemistry..., production of hydroxyl radicals, hydrogen atoms, hydrogen peroxide and aquated electrons. The chemical changes of compounds in water pulsed with these different sources of power are induced in part by the violent collapse of cavitation bubbles...

Hoffmann, M. R.

162

Radiation induced cavitation: A possible phenomenon in liquid targets?  

SciTech Connect

The proposed design of a new, short-pulse spallation neutron source includes a liquid mercury target irradiated with a 1 GeV proton beam. This paper explores the possibility that cavitation bubbles may be formed in the mercury and briefly discusses some design features that could avoid harmful effects should cavitation take place.

West, C.D.

1998-07-01

163

Simultaneous pressure measurement and high-speed photography study of cavitation in a dynamically loaded journal bearing  

NASA Technical Reports Server (NTRS)

Cavitation of the oil film in a dynamically loaded journal bearing was studied using high-speed photography and pressure measurement simultaneously. Comparison of the visual and pressure data provided considerable insight into the occurrence and nonoccurrence of cavitation. It was found that (1) for the submerged journal bearing, cavitation typically occurred in the form of one bubble with the pressure in the cavitation bubble close to the absolute zero; and (2) for cavitation-producing operating conditions, cavitation did not always occur; with the oil film then supporting a tensile stress.

Sun, D. C.; Brewe, David E.; Abel, Philip B.

1994-01-01

164

Experimental investigation on noise of cavitation nozzle and its chaotic behaviour  

NASA Astrophysics Data System (ADS)

The researches of cavitation noise mainly focus on the incipiency and developing of cavitation to prevent the cavititation erosion in the hydraulic machinery, while there is few report about the collapse strength of cavitation bubbles produced by water jet through the cavitation nozzle to utilize efficiently the collapse energy of cavitation bubbles. The cavitation noise signals are collected with hydrophones for the cavitation nozzle and general nozzle at the target position and the nozzle exit separately in the conditions of different standoff distance. The features of signal's frequency spectrum and power spectrum are analyzed for various nozzles by way of classical methods. Meanwhile, based on chaotic theory, phase space reconstruction is processed and the maximum Lyapunov index is calculated separately for each cavitation signal's time series. The results of chaotic analysis are compared with the one of conventional analysis. The analyzed data show that there are the marked differences at the spectrum between the cavitation nozzle and general nozzle at the target position while the standoff distance is 35 mm, which mainly displays at the high frequency segment (60-120 kHz). The maximum Lyapunov index calculated appear at standoff distance 35 mm, which is an optimum standoff distance for the most bubbles to collapse at the target. At the nozzle exit, the noise signal of cavitation nozzle is different from the general nozzle, which also displays at the high frequency segment. The results demonstrate that the water jet modulated by the cavitation nozzle can produce effectually cavitation, and at the target position the amplitude and energy of noise spectrum in high frequency segment for cavitation nozzle are higher than conventional nozzle and the Lyapunov index of cavitation nozzle is larger than conventional nozzle as the standoff distance is less than 55 mm. The proposed research reveals that the cavitation noise produced by collapse of cavitation bubbles attributes mainly to the high frequency segment of the spectrum, which provides references for the research on cavitation noise.

Zhang, Fenghua; Liu, Haifeng; Xu, Junchao; Tang, Chuanlin

2013-07-01

165

Bubble Baryogenesis  

E-print Network

We propose an alternative mechanism of baryogenesis in which a scalar baryon undergoes a percolating first-order phase transition in the early Universe. The potential barrier that divides the phases contains explicit B and CP violation and the corresponding instanton that mediates decay is therefore asymmetric. The nucleation and growth of these asymmetric bubbles dynamically generates baryons, which thermalize after percolation; bubble collision dynamics can also add to the asymmetry yield. We present an explicit toy model that undergoes bubble baryogenesis, and numerically study the evolution of the baryon asymmetry through bubble nucleation and growth, bubble collisions, and washout. We discuss more realistic constructions, in which the scalar baryon and its potential arise amongst the color-breaking minima of the MSSM, or in the supersymmetric neutrino seesaw mechanism. Phenomenological consequences, such as gravitational waves, and possible applications to asymmetric dark-matter generation are also discussed.

Clifford Cheung; Alex Dahlen; Gilly Elor

2012-05-15

166

Inertial confinement fusion based on the ion-bubble trigger  

NASA Astrophysics Data System (ADS)

Triggering the ion-bubble in an inertial confinement fusion, we have developed a novel scheme for the fast ignition. This scheme relies on the plasma cavitation by the wake of an intense laser pulse to generate an ion-bubble. The bubble acts both as an intense electron accelerator and as an electron wiggler. Consequently, the accelerated electrons trapped in the bubble can emit an intense tunable laser light. This light can be absorbed by an ablation layer on the outside surface of the ignition capsule, which subsequently drills it and thereby produces a guide channel in the pellet. Finally, the relativistic electron beam created in the bubble is guided through the channel to the high density core igniting the fusion fuel. The normalized beam intensity and beam energy required for triggering the ignition have been calculated when core is heated by the e-beam. In addition, through solving the momentum transfer, continuity and wave equations, a dispersion relation for the electromagnetic and space-charge waves has been analytically derived. The variations of growth rate with the ion-bubble density and electron beam energy have been illustrated. It is found that the growth rates of instability are significantly controlled by the ions concentration and the e-beam energy in the bubble.

Jafari, S.; Nilkar, M.; Ghasemizad, A.; Mehdian, H.

2014-10-01

167

Membrane disruption by optically controlled microbubble cavitation  

E-print Network

surface, the bubbles tend to collapse asymmetrically, often forming fast-moving liquid jets that may generation in diagnostic ultrasound imaging, it is possible that such cavitation could also lead to jet the mechanism during low-intensity insonation is clear8 , experimental corroboration for higher pressure regimes

Loss, Daniel

168

Controlled cavitation in microfluidics Severine Le Gac,2  

E-print Network

. At the center of a 20 µm thick and 1 mm wide channel pancake-shaped bubbles expand and collapse radially any ma- terial in contact with high speed flows; cavitation causes wear on pump blades, at bends. The bubble is generated with an ex- panded beam from a pulsed and frequency-doubled Nd:YAG laser (Solo PIV

Ohl, Claus-Dieter

169

An experimental investigation of acoustic cavitation in gaseous liquids  

Microsoft Academic Search

High amplitude radial pulsations of a single bubble in several glycerine and water mixtures were observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa at 21 to 25 kHz. Sonoluminescence, a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring

Dario F. Gaitan; Lawrence A. Crum

1990-01-01

170

Removal of residual nuclei following a cavitation event using low-amplitude ultrasound.  

PubMed

Microscopic residual bubble nuclei can persist on the order of 1 s following a cavitation event. These bubbles can limit the efficacy of ultrasound therapies such as shock wave lithotripsy and histotripsy, because they attenuate pulses that arrive subsequent to their formation and seed repetitive cavitation activity at a discrete set of sites (cavitation memory). Here, we explore a strategy for the removal of these residual bubbles following a cavitation event, using low-amplitude ultrasound pulses to stimulate bubble coalescence. All experiments were conducted in degassed water and monitored using high-speed photography. In each case, a 2-MHz histotripsy transducer was used to initiate cavitation activity (a cavitational bubble cloud), the collapse of which generated a population of residual bubble nuclei. This residual nuclei population was then sonicated using a 1 ms pulse from a separate 500-kHz transducer, which we term the bubble removal pulse. Bubble removal pulse amplitudes ranging from 0 to 1.7 MPa were tested, and the backlit area of shadow from bubbles remaining in the field following bubble removal was calculated to quantify efficacy. It was found that an ideal amplitude range exists (roughly 180 to 570 kPa) in which bubble removal pulses stimulate the aggregation and subsequent coalescence of residual bubble nuclei, effectively removing them from the field. Further optimization of bubble removal pulse sequences stands to provide an adjunct to cavitation-based ultrasound therapies such as shock wave lithotripsy and histotripsy, mitigating the effects of residual bubble nuclei that currently limit their efficacy. PMID:25265172

Duryea, Alexander P; Cain, Charles A; Tamaddoni, Hedieh A; Roberts, William W; Hall, Timothy L

2014-10-01

171

Removal of Residual Nuclei Following a Cavitation Event using Low-Amplitude Ultrasound  

PubMed Central

Microscopic residual bubble nuclei can persist on the order of 1 second following a cavitation event. These bubbles can limit the efficacy of ultrasound therapies such as shock wave lithotripsy and histotripsy, as they attenuate pulses that arrive subsequent to their formation and seed repetitive cavitation activity at a discrete set of sites (cavitation memory). Here, we explore a strategy for the removal of these residual bubbles following a cavitation event, using low amplitude ultrasound pulses to stimulate bubble coalescence. All experiments were conducted in degassed water and monitored using high speed photography. In each case, a 2 MHz histotripsy transducer was used to initiate cavitation activity (a cavitational bubble cloud), the collapse of which generated a population of residual bubble nuclei. This residual nuclei population was then sonicated using a 1 ms pulse from a separate 500 kHz transducer, which we term the ‘bubble removal pulse.’ Bubble removal pulse amplitudes ranging from 0 to 1.7 MPa were tested, and the backlit area of shadow from bubbles remaining in the field following bubble removal was calculated to quantify efficacy. It was found that an ideal amplitude range exists (roughly 180 – 570 kPa) in which bubble removal pulses stimulate the aggregation and subsequent coalescence of residual bubble nuclei, effectively removing them from the field. Further optimization of bubble removal pulse sequences stands to provide an adjunct to cavitation-based ultrasound therapies such as shock wave lithotripsy and histotripsy, mitigating the effects of residual bubble nuclei that currently limit their efficacy. PMID:25265172

Duryea, Alexander P.; Cain, Charles A.; Tamaddoni, Hedieh A.; Roberts, William W.; Hall, Timothy L.

2014-01-01

172

Numerical investigation of volume of fluid and level set interface capturing methods for bubble growth and detachment  

NASA Astrophysics Data System (ADS)

The injection of an air bubble in a liquid at rest is an interface flow problem where surface tension and its modeling at solid boundaries is a key factor. It is the subject of this study. Numerical simulations have been performed to study 3D axi-symmetrical bubble growth from an orifice through a horizontal wall. The gas inflow velocity used was sufficiently small to ensure that the bubble growth is quasi-static so that surface tension and buoyancy forces are dominant. The wall was considered non-wettable to avoid spreading of the interface along the wall. The Navier-Stokes equations were solved with two different interface capturing methods based on Volume of Fluid (VOF) and Level Set (LS) as well as coupled CVOFLS. In the VOF method the bubble interface was tracked using either an algebraic solver which results in some diffusion of the interface (compressive scheme implemented in OpenFOAM), or it was determined using a geometric reconstruction scheme (Geo-Reconstruct Scheme from Fluent). The TransAT code was used for the LS model which captures the interface using signed distance function. The bubble volume and center of gravity have been investigated during the growth using the three solvers and numerical results have been assessed against experimental data. These results have shown that reconstructing the interface using the LS method gives good agreement with the experiments. In VOF (compressive scheme), the bubble detaches at earlier times resulting in a smaller detachment volume. The coupled CVOFLS-GeoReconstruct was found to be more computationally expensive than the VOF-GeoReconstruct and to present bubble oscillation during the growth.

Albadawi, Abdulaleem; Delauré, Yan; Donoghue, David B.; Robinson, Anthony; Murray, Darina B.

2012-11-01

173

High-speed motion picture camera experiments of cavitation in dynamically loaded journal bearings  

NASA Technical Reports Server (NTRS)

A high-speed camera was used to investigate cavitation in dynamically loaded journal bearings. The length-diameter ratio of the bearing, the speeds of the shaft and bearing, the surface material of the shaft, and the static and dynamic eccentricity of the bearing were varied. The results reveal not only the appearance of gas cavitation, but also the development of previously unsuspected vapor cavitation. It was found that gas cavitation increases with time until, after many hundreds of pressure cycles, there is a constant amount of gas kept in the cavitation zone of the bearing. The gas can have pressures of many times the atmospheric pressure. Vapor cavitation bubbles, on the other hand, collapse at pressures lower than the atmospheric pressure and cannot be transported through a high-pressure zone, nor does the amount of vapor cavitation in a bearing increase with time. Analysis is given to support the experimental findings for both gas and vapor cavitation.

Jacobson, B. O.; Hamrock, B. J.

1982-01-01

174

Bursting Bubbles and Bilayers  

PubMed Central

This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition - in particular, poly (ethylene glyclol) (PEG) - is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power) with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented, including those involving microbubbles to deliver cargo into a cell, and those - not necessarily involving microubbles - to release cargo from a phospholipid vesicle (or reverse sonoporation). It is shown that the rate of (reverse) sonoporation from liposomes correlates with phospholipid bilayer phase behavior, liquid-disordered phases giving appreciably faster release than liquid-ordered phases. Moreover, liquid-disordered phases exhibit evidence of two release mechanisms, which are described well mathematically by enhanced diffusion (possibly via dilation of membrane phospholipids) and irreversible membrane disruption, whereas liquid-ordered phases are described by a single mechanism, which has yet to be positively identified. The ability to tune release kinetics with bilayer composition makes reverse sonoporation of phospholipid vesicles a promising methodology for controlled drug delivery. Moreover, nesting of microbubbles inside vesicles constitutes a truly “theranostic” vehicle, one that can be used for both long-lasting, safe imaging and for controlled drug delivery. PMID:23382772

Wrenn, Steven P.; Dicker, Stephen M.; Small, Eleanor F.; Dan, Nily R.; Mleczko, Michal; Schmitz, Georg; Lewin, Peter A.

2012-01-01

175

Cavitation dynamics and directional microbubble ejection induced by intense femtosecond laser pulses in liquids.  

PubMed

We study cavitation dynamics when focusing ring-shaped femtosecond laser beams in water. This focusing geometry reduces detrimental nonlinear beam distortions and enhances energy deposition within the medium, localized at the focal spot. We observe remarkable postcollapse dynamics of elongated cavitation bubbles with high-speed ejection of microbubbles out of the laser focal region. Bubbles are ejected along the laser axis in both directions (away and towards the laser). The initial shape of the cavitation bubble is also seen to either enhance or completely suppress jet formation during collapse. In the absence of jetting, microbubble ejection occurs orthogonal to the laser propagation axis. PMID:23031010

Faccio, D; Tamošauskas, G; Rubino, E; Darginavi?ius, J; Papazoglou, D G; Tzortzakis, S; Couairon, A; Dubietis, A

2012-09-01

176

Interferometric study on the growth of pulsed-laser-generated submicron bubble layer on a solid surface  

SciTech Connect

The effective thickness of a layer of rapidly growing multiple bubbles on a chromium surface is measured using the optical interference technique. Irradiation of nanosecond pulsed KrF excimer laser beam on a solid surface immersed in water induces explosive vaporization of water accompanying the temperature rise and pressure pulse generation. The transient growth of the bubble layer is measured by monitoring the optical path length change of the probe laser beam. This paper presents, for the first time, a noncontact technique for quantifying the transient behavior and growth rate of a submicron-thickness bubble layer at a nanosecond time scale. Comparison of the results with those from the optical reflectance and forward scattering measurements suggests that separate bubbles begin to grow in the early stage right after the laser-pulse irradiation and that they tend to coalesce in a later stage. The measured maximum bubble-layer thickness is about 0.1--0.3 {micro}m for laser fluences ranging from 50 to 70 mJ/cm{sup 2}.

Kim, D.; Park, H.K.; Grigoropoulos, C.P. [Univ. of California, Berkeley, CA (United States). Dept. of Mechanical Engineering

1996-12-31

177

Observation of cavitation in a mechanical heart valve in a total artificial heart.  

PubMed

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. The cause of cavitation in mechanical heart valves was investigated using the 25 mm Medtronic Hall valve and the 23 mm Omnicarbon valve. Closing of these valves in the mitral position was simulated in an electrohydraulic totally artificial heart. Tests were conducted under physiologic pressures at heart rates from 60 to 100 beats per minute with cardiac outputs from 4.8 to 7.7 L/min. The disk closing motion was measured by a laser displacement sensor. A high-speed video camera was used to observe the cavitation bubbles in the mechanical heart valves. The maximum closing velocity of the Omnicarbon valve was faster than that of the Medtronic Hall valve. In both valves, the closing velocity of the leaflet, used as the cavitation threshold, was approximately 1.3-1.5 m/s. In the case of the Medtronic Hall valve, cavitation bubbles were generated by the squeeze flow and by the effects of the venturi and the water hammer. With the Omnicarbon valve, the cavitation bubbles were generated by the squeeze flow and the water hammer. The mechanism leading to the development of cavitation bubbles depended on the valve closing velocity and the valve stop geometry. Most of the cavitation bubbles were observed around the valve stop and were generated by the squeeze flow. PMID:15171470

Lee, Hwansung; Tsukiya, Tomonori; Homma, Akihiko; Kamimura, Tadayuki; Takewa, Yoshiaki; Nishinaka, Tomohiro; Tatsumi, Eisuke; Taenaka, Yoshiyuki; Takano, Hisateru; Kitamura, Soichiro

2004-01-01

178

ELSEVIER Earth and Planetary Science Letters 160 (1998) 763776 Bubble growth in highly viscous melts: theory, experiments, and  

E-print Network

rocks and the formation of pyroclastic flows. © 1998 Elsevier Science B.V. All rights reserved. Keywords The volcanic eruptions associated with formation of lava domes in Mount St. Helens, Mount Unzen, and recently in initiating pyroclastic flows [6,7]. The exsolution of water and the growth of bubbles may play an impor- tant

Lyakhovsky, Vladimir

179

Effect of nuclei concentration on cavitation cluster dynamics.  

PubMed

Cavitation cluster dynamics after the passage of a single pressure wave is studied for different concentrations of artificial cavitation nuclei (30 to 3x10(5) nuclei/ml). With increasing concentration of cavitation nuclei the lifetime of the cavitation cluster is prolonged. Additionally, it is found that the spatial extent of the cluster decreases with higher nuclei concentration. The experimental data for concentrations less than 400 nuclei/ml are compared to simulations with a Rayleigh-Plesset-type equation, taking into account bubble-bubble interaction. For higher concentrations (more than 1000 nuclei/ml) the observed radial cluster dynamics is compared with calculations from an axisymmetric cavity-collapse model. PMID:17552694

Arora, M; Ohl, C D; Lohse, D

2007-06-01

180

Calcium Is a Major Determinant of Xylem Vulnerability to Cavitation  

PubMed Central

Xylem vulnerability to cavitation is a key parameter in the drought tolerance of trees, but little is known about the control mechanisms involved. Cavitation is thought to occur when an air bubble penetrates through a pit wall, and would hence be influenced by the wall's porosity. We first tested the role of wall-bound calcium in vulnerability to cavitation in Fagus sylvatica. Stems perfused with solutions of oxalic acid, EGTA, or sodium phosphate (NaPO4) were found to be more vulnerable to cavitation. The NaPO4-induced increase in vulnerability to cavitation was linked to calcium removal from the wall. In contrast, xylem hydraulic conductance was unaffected by the chemical treatments, demonstrating that the mechanisms controlling vulnerability to cavitation and hydraulic resistance are uncoupled. The NaPO4 solution was then perfused into stems from 13 tree species possessing highly contrasted vulnerability to cavitation. Calcium was found to be a major determinant of between-species differences in vulnerability to cavitation. This was evidenced in angiosperms as well as conifer species, thus supporting the hypothesis of a common mechanism in drought-induced cavitation. PMID:20547703

Herbette, Stephane; Cochard, Herve

2010-01-01

181

Numerical investigations of shock–bubble interactions in mercury  

Microsoft Academic Search

The bubble collapse induced by the shock–bubble interactions in mercury is investigated numerically to evaluate the cavitation damage. The ghost fluid method (GFM) is applied to the present analysis. Riemann solutions are utilized to correct the values at boundary nodes to suppress the pressure oscillations near the interface. The interactions between an air bubble and a plane shock wave in

Hiroyuki Takahira; Takahiro Matsuno; Keisuke Shuto

2008-01-01

182

Probability of cavitation for single ultrasound pulses applied to tissues and tissue-mimicking materials  

PubMed Central

In this article, the negative pressure values at which inertial cavitation consistently occurs in response to a single, 2-cycle, focused ultrasound pulse were measured in several media relevant to cavitation-based ultrasound therapy. The pulse was focused into a chamber containing one of the media, which included liquids, tissue-mimicking materials, and ex-vivo canine tissue. Focal waveforms were measured by two separate techniques using a fiber-optic hydrophone. Inertial cavitation was identified by high-speed photography in optically transparent media and an acoustic passive cavitation detector. The probability of cavitation (Pcav) for a single pulse as a function of peak negative pressure (p?) followed a sigmoid curve, with the probability approaching 1 when the pressure amplitude was sufficient. The statistical threshold (defined as Pcav = 0.5) was between p? = 26.0–30.0 MPa in all samples with a high water content, but varied between p? = 13.7 to > 36 MPa for other media. A model for radial cavitation bubble dynamics was employed to evaluate the behavior of cavitation nuclei at these pressure levels. A single bubble nucleus with an inertial cavitation threshold of p? = 28.2 MPa was estimated to have a 2.5 nm radius in distilled water. These data may be valuable for cavitation-based ultrasound therapy to predict the likelihood of cavitation at different pressure levels and dimensions of cavitation-induced lesions in tissue. PMID:23380152

Maxwell, Adam D.; Cain, Charles A.; Hall, Timothy L.; Fowlkes, J. Brian; Xu, Zhen

2012-01-01

183

Comments on the possibility of cavitation in liquid metal targets for pulsed spallation neutron sources  

SciTech Connect

When short pulses of protons strike the volume of a liquid target, the rapid heating produces a pressurized region which relaxes as the pressure wave propagates outward. Skala and Bauer have modeled the effects of the pressure wave impinging on the container walls of a liquid mercury target under ESS conditions. They find that high pressures and high wall stresses result if the medium is uniform, nearly incompressible liquid. The pressure and the stresses are much reduced if the liquid contains bubbles of helium, due to their high compressibility. However, according to the calculation, the pressure still reaches an atmosphere or so at the surface, which reflects the compressive wave as a rarefaction wave of the same magnitude. Even such modest underpressures can lead to the growth of bubbles (cavitation) at or near the surface, which can collapse violently and erode the container surface. It is necessary to avoid this. Leighton provides a wide ranging discussion of pressure waves in bubbly media, which may provide insights into the nature and control of cavitation phenomena. The paper surveys some of the relevant information from that source.

Carpenter J.M. [Argonne National Lab., IL (United States)

1996-06-01

184

Power spectrum of fluctuation for ultrasonic cavitation process in glycerin  

NASA Astrophysics Data System (ADS)

Experiments were carried out on ultrasonic cavitation in glycerin. The zone near the emitter has a structure from interacting gas-vapor bubbles; this structure takes the form of fractal clusters. The photometry of passed laser emission was the tool for studying dynamics of fluctuations. In transitive mode, the power spectrum of fluctuation varies by the law inversely proportional to frequency. Distributions of local fluctuations are different from Gaussian and exhibit the property of scale invariance. The qualitative behavior of the frequency dependence of the spectral fluctuation density was tested while varying the power of the ultrasonic emitter. It was demonstrated that the growth of the high-frequency margin of flicker-type behavior evidences for growing instability and can be considered as a forerunner of possible large-scale outbursts.

Skokov, V. N.; Koverda, V. P.; Reshetnikov, A. V.; Vinogradov, A. V.

2007-03-01

185

AN EFFICIENT TREATMENT STRATEGY FOR HISTOTRIPSY BY REMOVING CAVITATION MEMORY  

PubMed Central

Cavitation memory effects occur when remnants of cavitation bubbles (nuclei) persist in the host medium and act as seeds for subsequent events. In pulsed cavitational ultrasound therapy, or histotripsy, this effect may cause cavitation to repeatedly occur at these seeded locations within a target volume, producing inhomogeneous tissue fractionation or requiring an excess number of pulses to completely homogenize the target volume. We hypothesized that by removing the cavitation memory, i.e., the persistent nuclei, the cavitation bubbles could be induced at random locations in response to each pulse; therefore, complete disruption of a tissue volume may be achieved with fewer pulses. To test the hypothesis, the cavitation memory was passively removed by increasing the intervals between successive pulses, ?t, from 2, 10, 20, 50 and 100, to 200 ms. Histotripsy treatments were performed in red blood cell tissue phantoms and ex vivo livers using 1-MHz ultrasound pulses of 10 cycles at P?/P+ pressure of 21/59 MPa. The phantom study allowed for direct visualization of the cavitation patterns and the lesion development process in real time using high-speed photography; the ex vivo tissue study provided validation of the memory effect in real tissues. Results of the phantom study showed an exponential decrease in the correlation coefficient between cavitation patterns in successive pulses from 0.5 ± 0.1 to 0.1 ± 0.1 as ?t increased from 2–200 ms; correspondingly, the lesion was completely fractionated with significantly fewer pulses for longer ?ts. In the tissue study, given the same number of therapy pulses, complete and homogeneous tissue fractionation with well-defined lesion boundaries was achieved only for ?t ? 100 ms. These results indicated that the removal of the cavitation memory resulted in more efficient treatments and homogeneous lesions. PMID:22402025

Wang, Tzu-Yin; Xu, Zhen; Hall, Timothy L.; Fowlkes, J. Brian; Cain, Charles A.

2012-01-01

186

Non-Newtonian effects on flow-generated cavitation and on cavitation in a pressure field  

NASA Technical Reports Server (NTRS)

Observations are presented which show that the stresses in a flow field of very dilute polymer are not well enough described by the Navier-Stokes equations to accurately predict cavitation. The contitutive equation for the particular polymer and concentration used is needed. The second-order fluid form in which accelerations are relatively important appears capable of explaining observed cavitation suppression by changing the pressure field due to flow. Bubble dynamics in stationary dilute polymer solutions are also examined and found to be little different from those in water.

Ellis, A. T.; Ting, R. Y.

1974-01-01

187

Kidney stone erosion by micro scale hydrodynamic cavitation and consequent kidney stone treatment.  

PubMed

The objective of this study is to reveal the potential of micro scale hydrodynamic bubbly cavitation for the use of kidney stone treatment. Hydrodynamically generated cavitating bubbles were targeted to the surfaces of 18 kidney stone samples made of calcium oxalate, and their destructive effects were exploited in order to remove kidney stones in in vitro experiments. Phosphate buffered saline (PBS) solution was used as the working fluid under bubbly cavitating conditions in a 0.75 cm long micro probe of 147 ?m inner diameter at 9790 kPa pressure. The surface of calcium oxalate type kidney stones were exposed to bubbly cavitation at room temperature for 5 to 30 min. The eroded kidney stones were visually analyzed with a high speed CCD camera and using SEM (scanning electron microscopy) techniques. The experiments showed that at a cavitation number of 0.017, hydrodynamic bubbly cavitation device could successfully erode stones with an erosion rate of 0.31 mg/min. It was also observed that the targeted application of the erosion with micro scale hydrodynamic cavitation may even cause the fracture of the kidney stones within a short time of 30 min. The proposed treatment method has proven to be an efficient instrument for destroying kidney stones. PMID:22476893

Perk, Osman Yavuz; ?e?en, Muhsincan; Gozuacik, Devrim; Ko?ar, Ali

2012-09-01

188

Vapor-Gas Bubble Evolution and Growth in Extremely Viscous Fluids Under Vacuum  

NASA Technical Reports Server (NTRS)

Formation of vapor and gas bubbles and voids is normal and expected in flow processes involving extremely viscous fluids in normal gravity. Practical examples of extremely viscous fluids are epoxy-like filler materials before the epoxy fluids cure to their permanent form to create a mechanical bond between two substrates. When these fluids flow with a free liquid interface exposed to vacuum, rapid bubble expansion process may ensue. Bubble expansion might compromise the mechanical bond strength. The potential sources for the origin of the gases might be incomplete out-gassing process prior to filler application; regasification due to seal leakage in the filler applicator; and/or volatiles evolved from cure reaction products formed in the hardening process. We embarked on a study that involved conducting laboratory experiments with imaging diagnostics in order to deduce the seriousness of bubbling caused by entrained air and volatile fluids under space vacuum and low gravity environment. We used clear fluids with the similar physical properties as the epoxy-like filler material to mimic the dynamics of bubbles. Another aspect of the present study was to determine the likelihood of bubbling resulting from dissolved gases nucleating from solution. These experimental studies of the bubble expansion are compared with predictions using a modified Rayleigh- Plesset equation, which models the bubble expansion.

Kizito, John; Balasubramaniam, R.; Nahra, Henry; Agui, Juan; Truong, Duc

2008-01-01

189

Modeling of Vapor Bubble Growth Under Nucleate Boiling Conditions in Reduced Gravity  

NASA Technical Reports Server (NTRS)

A dynamic model is developed to describe the evolution of a vapor bubble growing at a nucleation site on a superheated surface under arbitrary gravity. The bubble is separated from the surface by a thin microlayer and grows due to the evaporation from the microlayer interface. The average thickness of the microlayer increases as the bubble expands along the surface if the evaporation rate is lower than some critical value. The corresponding threshold value of the surface temperature has to be associated with the burn-out crisis. Two main reasons make for bubble separation, which are the buoyancy force and a force caused by the vapor momentum that comes to the bubble with vapor molecules. The latter force is somewhat diminished if condensation takes place at the upper bubble surface in subcooled liquids. The action of the said forces is opposed by inertia of the additional mass of liquid as the bubble center rises above the surface and by inertia of liquid being expelled by the growing bubble in radial directions. An extra pressure force arises due to the liquid inflow into the microlayer with a finite velocity. The last force helps in holding the bubble close to the surface during an initial stage of bubble evolution. Two limiting regimes with distinctly different properties can be singled out, depending on which of the forces that favor bubble detachment dominates. Under conditions of moderately reduced gravity, the situation is much the same as in normal gravity, although the bubble detachment volume increases as gravity diminishes. In microgravity, the buoyancy force is negligible. Then the bubble is capable of staying near the surface for a long time, with intensive evaporation from the microlayer. It suggests a drastic change in the physical mechanism of heat removal as gravity falls below a certain sufficiently low level. Inferences of the model and conclusions pertaining to effects caused on heat transfer processes by changes in bubble hydrodynamics induced by gravity are discussed in connection with experimental evidence, both available in current and in as yet unpublished literature.

Buyevich, Yu A.; Webbon, Bruce W.

1995-01-01

190

Magnetic resonance imaging of velocity fields, the void fraction and gas dynamics in a cavitating liquid  

Microsoft Academic Search

In acoustic cavitation, the relationship between the bubble dynamics on the microscale and the flow properties on the macroscale is critical in determining sonochemical reaction kinetics. A new technique was developed to measure the void fraction and estimate water mobility in the vicinity of cavitating bubbles using phase-encoded magnetic resonance imaging with short characteristic measurement timescales (0.1-1 ms). The exponential

Igor V. Mastikhin; Aidin Arbabi; Benedict Newling; Abdelhaq Hamza; Alexander Adair

2011-01-01

191

Feasibility of noninvasive cavitation-guided blood-brain barrier opening using focused ultrasound and microbubbles in nonhuman primates  

NASA Astrophysics Data System (ADS)

In vivo transcranial and noninvasive cavitation detection with blood-brain barrier (BBB) opening in nonhuman primates is hereby reported. The BBB in monkeys was opened transcranically using focused ultrasound (FUS) in conjunction with microbubbles. A passive cavitation detector, confocal with the FUS transducer, was used to identify and monitor the bubble behavior. During sonication, the cavitation spectrum, which was found to be region-, pressure-, and bubble-dependent, provided real-time feedback regarding the opening occurrence and its properties. These findings demonstrate feasibility of transcranial, cavitation-guided BBB opening using FUS and microbubbles in noninvasive human applications.

Tung, Yao-Sheng; Marquet, Fabrice; Teichert, Tobias; Ferrera, Vincent; Konofagou, Elisa E.

2011-04-01

192

On the Growth Phase of Large-Scale Wave Structure and Plasma Bubbles  

NASA Astrophysics Data System (ADS)

For those interested in understanding the day-to-day variability in the occurrence of equatorial plasma bubbles (EPBs), it is important to realize that (1) EPBs are spawned and launched from the crests of large-scale wave structure (LSWS) that develop in the bottomside of the equatorial F layer, and (2) LSWS appears to develop during the post-sunset rise (PSSR) of the F layer. The implication is strong that the process is not just a random seeding that occurs during the course of a night, as might be expected from atmospheric gravity waves. This behavior is consistent with observations that have shown that most EPBs are launched at the end of the PSSR, or soon thereafter. The focus should be, therefore, to determine how LSWS is excited and amplified during the PSSR, which includes E region sunset. The major obstacle, to date, has been the lack of diagnostic sensors that are capable of probing into the base of the F layer, where the plasma densities are low, and detecting (preferably describing) LSWS during its growth phase. Some progress toward this end has been made, however, through use of ALTAIR, a steerable incoherent-scatter radar, and newly found signatures of LSWS in ionograms. Results are also expected to be forthcoming from total electron content measurements that can be made using radio beacons on board the low-inclination-orbiting C/NOFS satellite. A brief review of this topic will be presented.

Tsunoda, R. T.

2009-05-01

193

Dynamics of contact angle during growth and detachment of a vapor bubble at a single nucleation site  

SciTech Connect

Nucleate boiling is an efficient means of heat transfer especially where high heat fluxes are involved. Contact angle is an important parameter needed in the mechanistic models for prediction of nucleate boiling heat transfer. The present study focuses on variation of contact angle with interface velocity for a single nucleating bubble on a silicon wafer. Photographic images are acquired during inception, growth and departure of a bubble and the data are reduced to determine the interface velocity and contact angle at each stage of its growth. The results indicate that the contact angle depends primarily on whether the front is advancing or receding. Its dependency on the interface velocity is found to be weak in the range studied. For the test surface of Silicon wafer tested and for water as the test liquid contact angles of 61{degree}, 55{degree} and 49{degree} are found for advancing front, static and receding fronts respectively.

Ramanujapu, N.; Dhir, V.K.

1999-07-01

194

Continuous culture of bacteriophage Q-beta using a cellstat with a bubble wall-growth scraper  

NASA Astrophysics Data System (ADS)

It has been shown that a virulent phage Q? can be cultured continuously in a cellstat which was developed to culture a bacteriophage fd for the study of molecular evolution. A cloned disadvantageous mutant was cultured to obtain a biological relaxation curve to selection/mutation equilibrium. A new technique for scraping off the wall growth by air bubbles is introduced. The scraper worked well in short-time cultivation of Q?. It has various advantages of a closed system.

Husimi, Yuzuru; Keweloh, Hans-Christian

1987-06-01

195

Experimental study and modeling of swelling and bubble growth in carbon nanofiber filled mesophase pitch during carbonization  

NASA Astrophysics Data System (ADS)

Graphite and all carbon bipolar plates show corrosion resistance in fuel cells and provide good electrical conductivity. These materials typically need to be individually machined, a time consuming and costly process. Mesophase pitch is used to manufacture carbon fibers and carbon-carbon composites. This material provides a good starting point for the production of a moldable, all carbon bipolar plate. However, processing of mesophase pitch to produce all carbon materials requires a time intensive oxidation step to prevent swelling during carbonization. In this work, carbon nanofibers were used to reduce swelling in mesophase pitch. It was found that the increase in viscosity with the addition of carbon nanofibers was responsible for the reduction in swelling. The influence of the filler became apparent above the percolation threshold. At loadings below the percolation threshold, the swelling of the mesophase pitch was not reduced after carbonization. The swelling of the mesophase pitch at a given carbon nanofiber loading was also dependent on the length of the carbon nanofibers. Longer carbon nanofibers led to greater increases in the viscosity of the melt and thus led to greater reduction in swelling. The final carbon product was evaluated for use as a low temperature fuel cell bipolar plate material. Constraining the mesophase pitch during carbonization led to a final product with strength and electrical conductivity comparable to current composite bipolar plate materials. The addition of micron size chopped glass fibers with a softening point near 850°C and carbon nanofibers led to a final product with air permeability less than that of graphite. A spherically symmetric, single bubble growth model was also developed. The model included temperature dependence, liquid to bubble mass transfer and reactions in the system. Results from simulations showed that that the increase in viscosity due to the addition of carbon nanofibers slows the growth of bubbles, but that the time scale of single bubble growth is much shorter than the time over which the foam grows. The single bubble growth model was deemed to be applicable to low loadings of carbon nanofiber, where the bubble size distribution in the final foam is narrow.

Calebrese, Christopher

196

Bubble nucleation, growth and coalescence during the 1997 Vulcanian explosions of Soufrière Hills Volcano, Montserrat  

NASA Astrophysics Data System (ADS)

Soufrière Hills Volcano had two periods of repetitive Vulcanian activity in 1997. Each explosion discharged the contents of the upper 0.5-2 km of the conduit as pyroclastic flows and fallout: frothy pumices from a deep, gas-rich zone, lava and breadcrust bombs from a degassed lava plug, and dense pumices from a transition zone. Vesicles constitute 1-66 vol.% of breadcrust bombs and 24-79% of pumices, all those larger than a few tens of µm being interconnected. Small vesicles (< few tens of µm) in all pyroclasts are interpreted as having formed syn-explosively, as shown by their presence in breadcrust bombs formed from originally non-vesicular magma. Most large vesicles (> few hundreds of µm) in pumices are interpreted as pre-dating explosion, implying pre-explosive conduit porosities up to 55%. About a sixth of large vesicles in pumices, and all those in breadcrust bombs, are angular voids formed by syn-explosive fracturing of amphibole phenocrysts. An intermediate-sized vesicle population formed by coalescence of the small syn-explosive bubbles. Bubble nucleation took place heterogeneously on titanomagnetite, number densities of which greatly exceed those of vesicles, and growth took place mainly by decompression. Development of pyroclast vesicle textures was controlled by the time interval between the onset of explosion-decompression and surface quench in contact with air. Lava-plug fragments entered the air quickly after fragmentation (˜ 10 s), so the interiors continued to vesiculate once the rinds had quenched, forming breadcrust bombs. Deeper, gas-rich magma took longer (˜ 50 s) to reach the surface, and vesiculation of resulting pumice clasts was essentially complete prior to surface quench. This accounts for the absence of breadcrusting on pumice clasts, and for the textural similarity between pyroclastic flow and fallout pumices, despite different thermal histories after leaving the vent. It also allowed syn-explosive coalescence to proceed further in the pumices than in the breadcrust bombs. Uniaxial boudinage of amphibole phenocrysts in pumices implies significant syn-explosive vesiculation even prior to magma fragmentation, probably in a zone of steep pressure gradient beneath the descending fragmentation front. Syn-explosive decompression rates estimated from vesicle number densities (> 0.3-6.5 MPa s - 1 ) are consistent with those predicted by previously published numerical models.

Giachetti, T.; Druitt, T. H.; Burgisser, A.; Arbaret, L.; Galven, C.

2010-06-01

197

Bubble size distribution in acoustic droplet vaporization via dissolution using an ultrasound wide-beam method.  

PubMed

Performance and efficiency of numerous cavitation enhanced applications in a wide range of areas depend on the cavitation bubble size distribution. Therefore, cavitation bubble size estimation would be beneficial for biological and industrial applications that rely on cavitation. In this study, an acoustic method using a wide beam with low pressure is proposed to acquire the time intensity curve of the dissolution process for the cavitation bubble population and then determine the bubble size distribution. Dissolution of the cavitation bubbles in saline and in phase-shift nanodroplet emulsion diluted with undegassed or degassed saline was obtained to quantify the effects of pulse duration (PD) and acoustic power (AP) or peak negative pressure (PNP) of focused ultrasound on the size distribution of induced cavitation bubbles. It was found that an increase of PD will induce large bubbles while AP had only a little effect on the mean bubble size in saline. It was also recognized that longer PD and higher PNP increases the proportions of large and small bubbles, respectively, in suspensions of phase-shift nanodroplet emulsions. Moreover, degassing of the suspension tended to bring about smaller mean bubble size than the undegassed suspension. In addition, condensation of cavitation bubble produced in diluted suspension of phase-shift nanodroplet emulsion was involved in the calculation to discuss the effect of bubble condensation in the bubble size estimation in acoustic droplet vaporization. It was shown that calculation without considering the condensation might underestimate the mean bubble size and the calculation with considering the condensation might have more influence over the size distribution of small bubbles, but less effect on that of large bubbles. Without or with considering bubble condensation, the accessible minimum bubble radius was 0.4 or 1.7 ?m and the step size was 0.3 ?m. This acoustic technique provides an approach to estimate the size distribution of cavitation bubble population in opaque media and might be a promising tool for applications where it is desirable to tune the ultrasound parameters to control the size distribution of cavitation bubbles. PMID:24360840

Xu, Shanshan; Zong, Yujin; Li, Wusong; Zhang, Siyuan; Wan, Mingxi

2014-05-01

198

The effect of bubble growth dynamics on the performance of a gas evolving electrode  

E-print Network

bubbles to determine the diffusion coefficient (in water) of air, oxygen and hydrogen. The effect of the liquid phase was investigated by measuring the rate of diffusion of air into sodium chloride solution, and sea water. Glas and PJestwater (15... bubbles to determine the diffusion coefficient (in water) of air, oxygen and hydrogen. The effect of the liquid phase was investigated by measuring the rate of diffusion of air into sodium chloride solution, and sea water. Glas and PJestwater (15...

Haque, Mohammad Shamsul

2012-06-07

199

A Study on the Mechanism for Cavitation in the Mechanical Heart Valves with an Electrohydraulic Total Artificial Heart  

NASA Astrophysics Data System (ADS)

It has been conceived that the mechanical heart valves mounted in an artificial heart close much faster than in vivo use, resulting in cavitation bubbles formation. In this study, the mechanisms for cavitation in mechanical heart valves (MHVs) is investigated with monoleaflet and bileaflet valves in the mitral position with an electrohydraulic total artificial heart (EHTAH). The valve-closing velocity and pressure-drop through the valve were done, and a high-speed video camera was employed to investigate the mechanism for MHVs cavitation. The valve-closing velocity and pressure-drop of the bileaflet valves were less than that of the monoleaflet valves. Most of the cavitation bubbles in the monoleaflet valves were observed next to the edge of the valve stop and the inner side of the leaflet. With the bileaflet valves, cavitation bubbles were concentrated along the leaflet tip. Also, the number density of cavitation bubbles in the bileaflet valves was less than that of the monoleaflet valves. The number density of cavitation bubbles increased with an increase in the valve-closing velocity and the valve stop area. It is established that squeeze flow holds the key to cavitation in the mechanical heart valve. In a viewpoint of squeeze flow, the bileaflet valve with slow valve-closing velocity and small valve stop area, is safer to prevent of blood cell damage than the monoleaflet valves.

Lee, Hwansung; Tsukiya, Tomonori; Homma, Akihiko; Kamimura, Tadayuki; Tatsumi, Eisuke; Taenaka, Yoshiyuki; Kitamura, Soichiro

200

Jet orientation of a collapsing bubble near a solid wall with an attached air bubble  

NASA Astrophysics Data System (ADS)

The interaction between a cavitation bubble and a non-oscillating air bubble attached to a horizontal polyvinyl chloride plate submerged in de-ionized water is investigated using a low-voltage spark-discharge setup. The attached air bubble is approximately hemi-spherical in shape, and its proximity to a spark-induced oscillating bubble (represented by the dimensionless stand-off distance H') determines whether or not a jet is formed in the oscillating bubble during its collapse. When the oscillating bubble is created close to the plate, it jets towards or away from the plate. The ratio of oscillating bubble oscillation time and the wall-attached bubble oscillation time (T ') is found to be an important parameter for determining the jet direction. This is validated with numerical simulations using an axial-symmetrical boundary element model. Our study highlights prospects in reducing cavitation damage with a stationary bubble, and in utilizing a cavitation collapse jet by controlling the jet's direction.

Goh, B. H. T.; Ohl, S. W.; Klaseboer, E.; Khoo, B. C.

2014-04-01

201

Single cell membrane poration by bubble-induced microjets in a microfluidic chip.  

PubMed

This paper demonstrates membrane poration of a single suspension cell due to a fast liquid microjet. The jet is formed during the collapse of a laser induced bubble created at a variable stand-off distance from the target cell. The cell is trapped by a converging structure within a microfluidic chip. The asymmetrical growth and collapse of the cavitation bubble next to the cell lead to the microjetting, which deforms and porates the cell membrane. In the experiments, the membrane porations of myeloma cells are probed with the uptake of trypan blue. Time-resolved studies of the diffusion of trypan blue show a marked dependency on the bubble dynamics, i.e. the stand-off distance. The penetration length of the dye increases with shorter distances. Numerical simulations of the diffusion process agree with larger pores formed on the cell membrane. This method allows for a fast, repeatable, and localized rupture of membranes of individual cells in suspension. PMID:23364762

Li, Z G; Liu, A Q; Klaseboer, E; Zhang, J B; Ohl, C D

2013-03-21

202

Dynamics of multiple bubbles, excited by femtosecond filament in water: Role of aberrations  

E-print Network

Using shadow photography, we observed microsecond time scale evolution of multiple cavitation bubbles, excited by tighty focused femtosecond laser pulse in water under supercritical power regime (~100 Pcr). In these extreme conditions high energy delivery into the microvolume of liquid sample leads to creation of single filament which becomes a source of cavitation region formation. When aberrations were added to the optical scheme the hot spots along the filament axis are formed. At high energies (more than 40uJ) filaments in these hot spots are fired and, as a result, complex pattern of cavitation bubbles is created. The bubbles can be isolated from each other or build exotic drop-shaped cavitation region, which evolution at the end of its life, before the final collapse, contains the jet emission. The dynamics of the cavitation pattern was investigated from pulse energy and focusing. We found that greater numerical aperture of the focusing optics leads to greater cavitation area length. The strong interact...

Potemkin, F V

2014-01-01

203

An experimental study of cavitation effects due to shock waves  

Microsoft Academic Search

Bubble dynamics, acoustic emissions and sonoluminescences due to cavitation in the focal area of an electromagnetic shock wave lithotripter have been studied. In our experiments we used different repetition rate of the shock waves. For low repetition rates we were able to relate our experimental results to theoretical predictions for a similar shock wave field of an electrohydraulic lithotripter. Using

A. Cwik; T. Richter; H. Ermert

1993-01-01

204

Power spectrum of fluctuation for ultrasonic cavitation process in glycerin  

Microsoft Academic Search

Experiments were carried out on ultrasonic cavitation in glycerin. The zone near the emitter has a structure from interacting gas-vapor bubbles; this structure takes the form of fractal clusters. The photometry of passed laser emission was the tool for studying dynamics of fluctuations. In transitive mode, the power spectrum of fluctuation varies by the law inversely proportional to frequency. Distributions

V. N. Skokov; V. P. Koverda; A. V. Reshetnikov; A. V. Vinogradov

2007-01-01

205

Evaluation and interpretation of bubble size distributions in pulsed megasonic fields  

NASA Astrophysics Data System (ADS)

The occurrence of acoustic cavitation is incorporating a multitude of interdependent effects that strongly depend on the bubble size. Therefore, bubble size control would be beneficial for biological and industrial processes that rely on acoustic cavitation. A pulsed acoustic field can result in bubble size control and the repeated dissolution and reactivation ("recycling") of potentially active bubbles. As a consequence, a pulsed field can strongly enhance cavitation activity. In this paper, we present a modified methodology for the evaluation of the active bubble size distribution by means of a combination of cavitation noise measurements and ultrasonic pulsing. The key component of this modified methodology is the definition of an upper size limit, below which bubbles—in between subsequent pulses—have to dissolve, in order to be sustainably recycled. This upper limit makes it possible to explain and link the enhancement of cavitation activity to a bubble size distribution. The experimentally determined bubble size distributions for different power densities are interpreted in the frame of numerical calculations of the oscillatory responses of the bubbles to the intermittent driving sound field. The distributions are found to be shaped by the size dependent interplay between bubble pulsations, rectified diffusion, coalescence, and the development of parametrically amplified shape instabilities. Also, a phenomenological reactivation-deactivation model is proposed to explain and quantify the observed enhancement of cavitation activity under pulsed, with respect to continuous sonication. In this model, the pulse-duration determines the magnitude of the reactivation of partially dissolved bubbles and the deactivation of activated bubbles by coalescence. It is shown that the subsequent recycling of previously active bubbles leads to an accumulation of cavitation activity, which saturates after a certain number of pulses. The model is fitted to the experimental data for the cavitation activity measured by means of ultraharmonic cavitation noise as a function of the pulse duration. Measurements of the development of the cavitation noise and sonochemiluminescence over a sequence of pulses for different pulse durations and separations confirm the general validity of the proposed model. Size distributions of the larger, inactive bubbles that were extracted from High-speed images of the cavitation field, relate the deactivation of activated bubbles by coalescence to the increase in volume concentrations of larger bubbles as observed by others.

Hauptmann, M.; Struyf, H.; De Gendt, S.; Glorieux, C.; Brems, S.

2013-05-01

206

Experimental and numerical analysis of cavitating flow around a hydrofoil  

NASA Astrophysics Data System (ADS)

The paper describes experiments carried out in the cavitation tunnel with the rectangular test section of 150 × 150 × 500 mm and the maximum test section inlet velocity of 25 m/s. These experiments have been aimed to visualize the cavitation phenomena as well as to quantify the erosion potential using pitting tests evaluated during the incubation period for the cast-iron prismatic hydrofoil with the modified NACA profile. A bypass section installed in the tunnel has allowed to measure the nuclei content in the inlet flow to the test section using the acoustic spectrometer. The measured data have been compared with the CFD analysis of the cavitation phenomena on the hydrofoil as well as the numerically determined location and magnitude of the first calculated collapses of the cavitating bubbles with a good agreement.

Sedlá?, Milan; Komárek, Martin; Vyroubal, Michal; Müller, Miloš

2012-04-01

207

Modelling of flow with cavitation in centrifugal pump  

NASA Astrophysics Data System (ADS)

The paper concerns flow modelling in centrifugal pump with special consideration of cavitation phenomena. Cavitation occurs when local pressure drops below the saturation pressure according to the temperature of the flow. Vapour bubbles are created and then they flow through the areas with higher pressure. The bubbles collapse rapidly generating pressure wave, noise and vibration. Working under cavitation condition is very dangerous to a pump and can significantly shorten its lifetime. The investigated centrifugal pump consists of three two-flow rotors and stators working on a single shaft. The modelling process started with grid independence study. When the grid was chosen, the pump performance curve was obtained using the single phase fluid model. Next, using the results from pump performance curve calculations, the cavitation characteristic was obtained. The constant capacity was held when the pressure at the inlet was reduced. The two - phase model was used with Zwart cavitation model. The results indicate that the pump work in safe range of parameters. The analysis also provides wide range of information about the areas of vapour appearance. The most endangered regions are leading edges of rotor. When pressure at the inlet drops to about one third of pressure that calculations started from the cavitation cloud appears in whole rotor. The intense of vapour bubbles creation is greater near the shroud of the pump, rather than near the hub. As cavitation is strongly unsteady phenomena, the transient calculations were performed to check if the results are close to those obtained using the steady state type. The differences are not significant.

Homa, D.; Wróblewski, W.

2014-08-01

208

Interaction of two differently sized oscillating bubbles in a free field  

NASA Astrophysics Data System (ADS)

Most real life bubble dynamics applications involve multiple bubbles, for example, in cavitation erosion prevention, ultrasonic baths, underwater warfare, and medical applications involving microbubble contrast agents. Most scientific dealings with bubble-bubble interaction focus on two similarly sized bubbles. In this study, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography. Four types of bubble behavior were observed, namely, jetting toward each other, jetting away from each other, bubble coalescence, and a behavior termed the “catapult” effect. In-phase bubbles jet toward each other, while out-of-phase bubbles jet away from each other. There exists a critical phase difference that separates the two regimes. The behavior of the bubbles is fully characterized by their dimensionless separation distance, their phase difference, and their size ratio. It is also found that for bubbles with large size difference, the smaller bubble behaves similarly to a single bubble oscillating near a free surface.

Chew, Lup Wai; Klaseboer, Evert; Ohl, Siew-Wan; Khoo, Boo Cheong

2011-12-01

209

Bubble dynamics in an acoustic flow field  

NASA Astrophysics Data System (ADS)

Dynamics of interaction between cavitational bubbles is investigated when a complex of a compression and a rarefaction pulse passes through a liquid with pre-existing micro bubbles. Cavitation was generated experimentally with the help of electromagnetic generator of a flat and a convergent acoustic pulse (2-mus duration, 1-20 MPa) having the form of a hollow sphere segment. A modeling was performed within the frame of two-dimensional axisymmetric nonstationary approach on the basis of conservation laws for a model of an ideal compressible liquid. A thermodynamic flow field was computed both in liquid and inside bubbles. Behind the rarefaction wave the microbubbles begin to grow and generate secondary compression shocks, the amplitude of which may exceed that of the incident pulse under certain conditions. It is shown that the process of bubble interaction within a cluster is accompanied by bubble coalescence, fragmentation, and collapse of the initial bubble or its fragments. Simultaneously, high temperature spots appear in the bubble compressing by the secondary wave. Adiabatic heating of gas either inside a bubble or near the neck between a bubble and its fragment may result in sonoluminescence, also observed in experiments. [Work supported by ASA, DAAD, and RFBR.

Voronin, Dmitry V.; Sankin, Georgij N.; Mettin, Robert; Teslenko, Vyacheslav S.; Lauterborn, Werner

2002-11-01

210

Experiments in thermosensitive cavitation of a cryogenic rocket propellant surrogate  

NASA Astrophysics Data System (ADS)

Cavitation is a phase-change phenomenon that may appear in practical devices, often leading to loss of performance and possible physical damage. Of particular interest is the presence of cavitation in rocket engine pumps as the cryogenic fluids cavitate in impellers and inducers. Unlike water, which has been studied exhaustively, cryogenic fluids undergo cavitation with significant thermal effect. Past attempts at analyzing this behavior in water have led to poor predictive capability due to the lack of data in the regime defined as thermosensitive cavitation. Fluids flowing near their thermodynamic critical point have a liquid-vapor density ratio that is orders of magnitude less than typical experimental fluids, so that the traditional equation-of-state and cavitation models do not apply. Thermal effects in cavitation have not been fully investigated due to experimental difficulties handling cryogenics. This work investigates the physical effects of thermosensitive cavitation in a model representative of a turbopump inducer in a modern rocket engine. This is achieved by utilizing a room-temperature testing fluid that exhibits a thermal effect equivalent to that experienced by cryogenic propellants. Unsteady surface pressures and high speed imaging collected over the span of thermophysical regimes ranging from thermosensitive to isothermal cavitation offer both quantitative and qualitative insight into the physical process of thermal cavitation. Physical and thermodynamic effects are isolated to identify the source of cavity conditions, oscillations and growth/collapse behavior. Planar laser imaging offers an instantaneous look inside the vapor cavity and at the behavior of the boundary between the two-phase region and freestream liquid. Nondimensional parameters are explored, with cavitation numbers, Reynolds Numbers, coefficient of pressure and nondimensional temperature in a broad range. Results in the form of cavitation regime maps, Strouhal Number of cavity collapse, and cavity length offer a mechanistic analysis of the phenomenon. Linear stability analysis of the boundary is performed, as well as analysis of the thermal effects in the cavity and the oscillatory behavior of the cavity and reentrant jet.

Kelly, Sean Benjamin

211

Bubble Proliferation in Shock Wave Lithotripsy Occurs during Inertial Collapse  

Microsoft Academic Search

In shock wave lithotripsy (SWL), firing shock pulses at slow pulse repetition frequency (0.5 Hz) is more effective at breaking kidney stones than firing shock waves (SWs) at fast rate (2 Hz). Since at fast rate the number of cavitation bubbles increases, it appears that bubble proliferation reduces the efficiency of SWL. The goal of this work was to determine

Yuri A. Pishchalnikov; James A. McAteer; Irina V. Pishchalnikova; James C. Williams; Michael R. Bailey; Oleg A. Sapozhnikov

2008-01-01

212

Bubble Proliferation in Shock Wave Lithotripsy Occurs during Inertial Collapse  

Microsoft Academic Search

In shock wave lithotripsy (SWL), firing shock pulses at slow pulse repetition frequency (0.5Hz) is more effective at breaking kidney stones than firing shock waves (SWs) at fast rate (2Hz). Since at fast rate the number of cavitation bubbles increases, it appears that bubble proliferation reduces the efficiency of SWL. The goal of this work was to determine the basis

Yuri A. Pishchalnikov; James A. McAteer; Irina V. Pishchalnikova; James C. Williams; Michael R. Bailey; Oleg A. Sapozhnikov

213

Luminescence from Tube-Arrest Bubbles in Pure Glycerin  

Microsoft Academic Search

Single transient cavitation bubble with luminescence has been generated in pure glycerin by using the `tube arrest' method. The analyses of high-speed photograph and light emission data suggest that the light emission would be a single bubble sonoluminescence. The luminescence pulse width is observed to vary from sub-nanosecond to about 30 ns. The width and intensity of luminescence pulses increases

Qi-Dai Chen; Long Wang

2004-01-01

214

Probing luminescence from nonspherical bubble collapse Claus-Dieter Ohl  

E-print Network

Probing luminescence from nonspherical bubble collapse Claus-Dieter Ohl Department of Applied May 2002; published 27 June 2002 The luminescence from single laser produced cavitation bubbles light emission events happen during a time interval of 80 ns. The luminescence duration increases

Ohl, Claus-Dieter

215

Mechanism for cavitation in the mechanical heart valve with an artificial heart: nuclei and viscosity dependence.  

PubMed

Until now, we have estimated cavitation for mechanical heart valves (MHV) mounted in an electrohydraulic total artificial heart (EHTAH) with tap water. However, tap water at room temperature is not a proper substitute for blood at 37 degrees C. We therefore investigated fluid characterization in studies of MHV cavitation associated with the viscosity and nuclei content of a testing fluid. We used the Medtronic Hall valve mounted in the mitral position of the EHTAH. As testing fluids, tap water, distilled water, and glycerin solution were used. The valve-closing velocity, pressure-drop measurements, and a high-speed video camera were employed to determine the cavitation intensity in MHV. Most of the cavitation bubbles were observed at the edge of the valve stop. Our analysis of the results indicates that squeeze flow is the major cause of cavitation in the Medtronic Hall valve. The cavitation intensity increased with increases in the fluid viscosity and the valve-closing velocity. Even if cavitation intensity in glycerin solution was greater, the cavitation occurrence probability was less in glycerin solution than in tap water. Our results suggest that tap water contains particles that cause an increase in the cavitation occurrence probability. We conclude that cavitation intensity is greatly affected by the nuclei concentration in the fluid and the fluid viscosity. PMID:15644082

Lee, Hwansung; Taenaka, Yoshiyuki; Kitamura, Soichiro

2005-01-01

216

Mechanical clot damage from cavitation during sonothrombolysis.  

PubMed

Recent studies have shown that high intensity focused ultrasound (HIFU) accelerates thrombolysis for ischemic stroke. Although the mechanisms are not fully understood, cavitation is thought to play an important role. The goal of this paper is to investigate the potential for cavitation to cause mechanical damage to a blood clot. The amount of damage to the fiber network caused by a single bubble expansion and collapse is estimated by two independent approaches: One based on the stretch of individual fibers and the other based on the energy available to break individual fibers. The two methods yield consistent results. The energy method is extended to the more important scenario of a bubble outside a blood clot that collapses asymmetrically creating an impinging jet. This leads to significantly more damage compared to a bubble embedded within the clot structure. Finally, as an example of how one can apply the theory, a simulation of the propagation of HIFU waves through model calvaria of varying density is explored. The maximum amount of energy available to cause damage to a blood clot increases as the density of the calvaria decreases. PMID:23654418

Weiss, Hope L; Selvaraj, Prashanth; Okita, Kohei; Matsumoto, Yoichiro; Voie, Arne; Hoelscher, Thilo; Szeri, Andrew J

2013-05-01

217

A Generalized Eulerian-Lagrangian Analysis, with Application to Liquid Flows with Vapor Bubbles  

NASA Technical Reports Server (NTRS)

Under a NASA MSFC SBIR Phase 2 effort an analysis has been developed for liquid flows with vapor bubbles such as those in liquid rocket engine components. The analysis is based on a combined Eulerian-Lagrangian technique, in which Eulerian conservation equations are solved for the liquid phase, while Lagrangian equations of motion are integrated in computational coordinates for the vapor phase. The novel aspect of the Lagrangian analysis developed under this effort is that it combines features of the so-called particle distribution approach with those of the so-called particle trajectory approach and can, in fact, be considered as a generalization of both of those traditional methods. The result of this generalization is a reduction in CPU time and memory requirements. Particle time step (stability) limitations have been eliminated by semi-implicit integration of the particle equations of motion (and, for certain applications, the particle temperature equation), although practical limitations remain in effect for reasons of accuracy. The analysis has been applied to the simulation of cavitating flow through a single-bladed section of a labyrinth seal. Models for the simulation of bubble formation and growth have been included, as well as models for bubble drag and heat transfer. The results indicate that bubble formation is more or less 'explosive'. for a given flow field, the number density of bubble nucleation sites is very sensitive to the vapor properties and the surface tension. The bubble motion, on the other hand, is much less sensitive to the properties, but is affected strongly by the local pressure gradients in the flow field. In situations where either the material properties or the flow field are not known with sufficient accuracy, parametric studies can be carried out rapidly to assess the effect of the important variables. Future work will include application of the analysis to cavitation in inducer flow fields.

Dejong, Frederik J.; Meyyappan, Meyya

1993-01-01

218

A generalized Eulerian-Lagrangian analysis, with application to liquid flows with vapor bubbles  

NASA Astrophysics Data System (ADS)

Under a NASA MSFC SBIR Phase 2 effort an analysis has been developed for liquid flows with vapor bubbles such as those in liquid rocket engine components. The analysis is based on a combined Eulerian-Lagrangian technique, in which Eulerian conservation equations are solved for the liquid phase, while Lagrangian equations of motion are integrated in computational coordinates for the vapor phase. The novel aspect of the Lagrangian analysis developed under this effort is that it combines features of the so-called particle distribution approach with those of the so-called particle trajectory approach and can, in fact, be considered as a generalization of both of those traditional methods. The result of this generalization is a reduction in CPU time and memory requirements. Particle time step (stability) limitations have been eliminated by semi-implicit integration of the particle equations of motion (and, for certain applications, the particle temperature equation), although practical limitations remain in effect for reasons of accuracy. The analysis has been applied to the simulation of cavitating flow through a single-bladed section of a labyrinth seal. Models for the simulation of bubble formation and growth have been included, as well as models for bubble drag and heat transfer. The results indicate that bubble formation is more or less 'explosive'. for a given flow field, the number density of bubble nucleation sites is very sensitive to the vapor properties and the surface tension. The bubble motion, on the other hand, is much less sensitive to the properties, but is affected strongly by the local pressure gradients in the flow field. In situations where either the material properties or the flow field are not known with sufficient accuracy, parametric studies can be carried out rapidly to assess the effect of the important variables. Future work will include application of the analysis to cavitation in inducer flow fields.

Dejong, Frederik J.; Meyyappan, Meyya

1993-07-01

219

Cavitation structures formed during the rebound of a sphere from a wetted surface  

NASA Astrophysics Data System (ADS)

We use high-speed imaging to observe the dynamics of cavitation, caused by the impact and subsequent rebound of a sphere from a solid surface covered with a thin layer of highly viscous liquid. We note marked qualitative differences between the cavitation structures with increase in viscosity, as well as between Newtonian and non-Newtonian liquids. The patterns observed are quite unexpected and intricate, appearing in concentric ring formations around the site of impact. In all cases, we identify a distinct radius from which the primary bubbles emanate. This radius is modelled with a modified form of Hertz contact theory. Within this radius, we show that some fine cavitation structure may exist or that it may be one large cavitation bubble. For the non-Newtonian fluids, we observe foam-like structures extending radially with diminishing bubble sizes with increase in radial position. Whereas for the Newtonian fluids, the opposite trend is observed with increasing bubble size for increasing radial position. Finally, we compare our experimental observations of cavitation to the maximum tension criterion proposed by Joseph (J Fluid Mech 366:367-378, 1998) showing that this provides the lower limit for the onset of cavitation in our experiments.

Marston, J. O.; Yong, W.; Ng, W. K.; Tan, R. B. H.; Thoroddsen, S. T.

2011-03-01

220

Direct calculation of bubble growth, departure, and rise in nucleate pool boiling  

Microsoft Academic Search

A mesh-free numerical method (MPS–MAFL) is presented for the analysis of gas–liquid two-phase flows. In this method, a particle method (MPS) is combined with a gridless method (MAFL) for an arbitrary-Lagrangian–Eulerian calculation. Gas–liquid two-phase flows are calculated directly by the present method with and without the phase change. As an isothermal flow, a gas bubble rising in viscous liquids is

Han Young Yoon; Seiichi Koshizuka; Yoshiaki Oka

2001-01-01

221

The growth kinetics of hydrate film on the surface of gas bubble suspended in water or aqueous surfactant solution  

NASA Astrophysics Data System (ADS)

A novel experimental method to study the hydrate formation kinetics on the gas/water interface was presented and, using this method, the two-dimensional growth kinetic data of hydrate film on the surface of quiescent methane gas bubble suspended in pure water, natural water and natural water added with different contents of sodium dodecyl sulfate (SDS) were measured and compared. The experimental results showed that the presence of the low dose of ions in natural water appreciably inhibited the hydrate formation; the presence of SDS promoted the hydrate growth when its concentration was lower than 1000 mg/L while it inhibited the hydrate formation beyond this region, the concentration of SDS corresponding to the most efficient promotion was determined to be 500 mg/L or so; the presence of low-dose ions in the natural water has little negative influence upon the promotion efficiency of SDS. A two-parameter kinetic model was developed to correlate the growth rates of hydrate films in different aqueous solutions consistently, where the dimensionless Gibbs free energy difference of hydrate formation reaction was chosen as driving force. Good agreement between calculated results and experimental data was achieved and only one parameter was found to be SDS concentration dependent. The mechanism that the presence of SDS affects the hydrate formation rate was discussed based on the experimental and theoretical results with some new insights. Additionally, the three-dimensional growth of hydrate shell covering the gas bubble was studied morphologically and a series of interesting phenomena were observed and discussed.

Sun, Chang-Yu; Chen, Guang-Jin; Ma, Chang-Feng; Huang, Qiang; Luo, Hu; Li, Qing-Ping

2007-08-01

222

Detection of cystic structures using pulsed ultrasonically induced resonant cavitation  

NASA Technical Reports Server (NTRS)

Apparatus and method for early detection of cystic structures indicative of ovarian and breast cancers uses ultrasonic wave energy at a unique resonance frequency for inducing cavitation in cystic fluid characteristic of cystic structures in the ovaries associated with ovarian cancer, and in cystic structures in the breast associated with breast cancer. Induced cavitation bubbles in the cystic fluid implode, creating implosion waves which are detected by ultrasonic receiving transducers attached to the abdomen of the patient. Triangulation of the ultrasonic receiving transducers enables the received signals to be processed and analyzed to identify the location and structure of the cyst.

Bar-Cohen, Yoseph (Inventor); Kovach, John S. (Inventor)

2002-01-01

223

Numerical Study on the Inhibition of Cavitation in Piping Systems  

NASA Astrophysics Data System (ADS)

Abrupt closing valve in piping systems is sometimes resulted in cavitation due to the occurrence of high pressure difference. The bubbles generating by cavitation influence operating pressure and then those generate shock wave and vibration. These phenomena can consequentially cause to corrosion and erosion. So, the cavitation is the important factor to consider reliability of piping systems and mechanical lifetime. This paper investigated the various inhibition methods of cavitation in piping systems in which butterfly valves are installed. To prevent cavitation occurrence, it is desirable to analyze its characteristics between the upstream and downstream of process valve. Results show that the fluid velocity is fast when a working fluid passed through butterfly valve. The pressure of these areas was not only under saturation vapor pressure of water, but also cavitation was continuously occurred. We confirmed that the effect of existence of inserted orifice and influence to break condition under saturation vapor pressure of water. Results were graphically depicted by pressure distribution, velocity distribution, and vapor volume fraction.

Byeon, Sun Seok; Lee, Sang Jun; Kim, Youn-Jea

224

Effect of geometrical parameters on submerged cavitation jet discharged from profiled central-body nozzle  

NASA Astrophysics Data System (ADS)

The flow characteristics of cavitation jets are essential issues among relevant studies. The physical properties of the jet are largely determined by the geometrical parameters of the nozzle. The structure and cavitation jets characteristics of the angular-nozzle and the self-resonating cavitation nozzle have been extensively studied, but little research is conducted in the central-body cavitation nozzle mainly because of its hard processing and the cavitation jet effect not satisfactory. In this paper, a novel central-body nozzle (a non-plunger central-body nozzle with square outlet) is studied to solve above problems. Submerged jets discharged from the novel central-body nozzle are simulated, employing the full cavitation model. The impact of nozzle configuration on jet properties is analyzed. The analysis results indicate that when central-body relative diameter keeps constant, there is an optimal contraction degree of nozzle's outlet, which can induce intense cavitation in the jet. The central-body relative diameter also affects jet profiles. In the case of large central-body relative diameter, most of the bubbles settle in the jet core. On the contrary, a smaller relative diameter makes bubbles concentrate in the interface between the jet and its surrounding fluid. Moreover, the shorter outlet part allows the cavitation zone further extend in both the axial and racial directions. The research results further consummate the study on the central-body nozzles and the correlation between cavitation jet and the structure, and elementarily reveal the mechanism of cavitation jet produced in a non-plunger novel central-body nozzle and the effect of the structure parameters on the cavitation jet, moreover, provide the theoretical basis for the optimal design of the nozzle.

Yang, Minguan; Xiao, Shengnan; Kang, Can; Wang, Yuli

2013-05-01

225

Cavitating flow investigation inside centrifugal impellers for a condensate pump  

NASA Astrophysics Data System (ADS)

In order to investigate the effect of blade inlet angle on centrifugal pump cavitation performance, numerical simulation of cavitating turbulent flow is conducted for a condensate pump with different impellers based on SST k-? turbulence model and a mixture cavitation model. The results indicate that for a condensate pump having meridional section with larger area at blade leading edge compared with conventional pumps, the reverse flows inside the blade-to-blade channels are not negligible. It is noted that large incidence at blade leading edge is helpful to improve the cavitation performance for the pump. The possible reason may be the growth of cavities inside the impeller has less influence on the flow in the channel between two neighboring blades. Further, uniform incidence angle along the blade leading edge is preferable for the improvement of cavitation performance.

Wei, W.; Luo, X. W.; Ji, B.; Zhuang, B. T.; Xu, H. Y.

2012-11-01

226

Mercury Cavitation Phenomenon in Pulsed Spallation Neutron Sources  

SciTech Connect

Innovative researches will be performed at Materials and Life Science Experimental Facility in J-PARC, in which a mercury target system will be installed as MW-class pulse spallation neutron sources. Proton beams will be injected into mercury target to induce the spallation reaction. At the moment the intense proton beam hits the target, pressure waves are generated in the mercury because of the abrupt heat deposition. The pressure waves interact with the target vessel leading to negative pressure that may cause cavitation along the vessel wall. Localized impacts by micro-jets and/or shock waves which are caused by cavitation bubble collapse impose pitting damage on the vessel wall. The pitting damage which degrades the structural integrity of target vessels is a crucial issue for high power mercury targets. Micro-gas-bubbles injection into mercury may be useful to mitigate the pressure wave and the pitting damage. The visualization of cavitation-bubble and gas-bubble collapse behaviors was carried out by using a high-speed video camera. The differences between them are recognized.

Futakawa, Masatoshi; Naoe, Takashi [Japan Atomic Energy Agency Tokai-mura, Naka-gun, Ibaraki-ken, 319-1195 (Japan); Kawai, Masayoshi [KEK Tsukuba-shi, Ibaraki-ken, 305-0801 (Japan)

2008-06-24

227

Mercury Cavitation Phenomenon in Pulsed Spallation Neutron Sources  

NASA Astrophysics Data System (ADS)

Innovative researches will be performed at Materials & Life Science Experimental Facility in J-PARC, in which a mercury target system will be installed as MW-class pulse spallation neutron sources. Proton beams will be injected into mercury target to induce the spallation reaction. At the moment the intense proton beam hits the target, pressure waves are generated in the mercury because of the abrupt heat deposition. The pressure waves interact with the target vessel leading to negative pressure that may cause cavitation along the vessel wall. Localized impacts by micro-jets and/or shock waves which are caused by cavitation bubble collapse impose pitting damage on the vessel wall. The pitting damage which degrades the structural integrity of target vessels is a crucial issue for high power mercury targets. Micro-gas-bubbles injection into mercury may be useful to mitigate the pressure wave and the pitting damage. The visualization of cavitation-bubble and gas-bubble collapse behaviors was carried out by using a high-speed video camera. The differences between them are recognized.

Futakawa, Masatoshi; Naoe, Takashi; Kawai, Masayoshi

2008-06-01

228

Low frequency cavitation erosion  

NASA Astrophysics Data System (ADS)

Damage of diesel engine piston sleeve liners due to cavitation of the coolant fluid can be severe. Coolant fluid additives are used to inhibit cavitation damage, and are evaluated by industry suppliers using ASTM G32-98 Standard Test Method for Cavitation Erosion Using Vibratory Apparatus. The ASTM G32-98 test procedure uses an ultrasonic horn at 20 kHz to vibrate a test button in the coolant. The test button mass loss and surface appearance are studied to sort the performance of new coolant additives. Mismatch between good lab performers and actual engine test runs has raised concerns over the current lab test. The frequency range of the current test has been targeted for investigation. A low frequency, less than 2000 Hz, test rig was built to explore the cavitation damage. The test system did produce cavitation on the surface of the test button for a period of 36 h, with minimal mass loss. The test rig experienced cyclic fatigue when test times were extended. The work is now focusing on designing a better test rig for long duration tests and on developing numerical models in order to explore the effects of cavitation excitation frequency on surface erosion.

Pardue, Sally J.; Chandekar, Gautam

2002-11-01

229

Detecting vapour bubbles in simulations of metastable water  

NASA Astrophysics Data System (ADS)

The investigation of cavitation in metastable liquids with molecular simulations requires an appropriate definition of the volume of the vapour bubble forming within the metastable liquid phase. Commonly used approaches for bubble detection exhibit two significant flaws: first, when applied to water they often identify the voids within the hydrogen bond network as bubbles thus masking the signature of emerging bubbles and, second, they lack thermodynamic consistency. Here, we present two grid-based methods, the M-method and the V-method, to detect bubbles in metastable water specifically designed to address these shortcomings. The M-method incorporates information about neighbouring grid cells to distinguish between liquid- and vapour-like cells, which allows for a very sensitive detection of small bubbles and high spatial resolution of the detected bubbles. The V-method is calibrated such that its estimates for the bubble volume correspond to the average change in system volume and are thus thermodynamically consistent. Both methods are computationally inexpensive such that they can be used in molecular dynamics and Monte Carlo simulations of cavitation. We illustrate them by computing the free energy barrier and the size of the critical bubble for cavitation in water at negative pressure.

González, Miguel A.; Menzl, Georg; Aragones, Juan L.; Geiger, Philipp; Caupin, Frederic; Abascal, Jose L. F.; Dellago, Christoph; Valeriani, Chantal

2014-11-01

230

Detecting vapour bubbles in simulations of metastable water.  

PubMed

The investigation of cavitation in metastable liquids with molecular simulations requires an appropriate definition of the volume of the vapour bubble forming within the metastable liquid phase. Commonly used approaches for bubble detection exhibit two significant flaws: first, when applied to water they often identify the voids within the hydrogen bond network as bubbles thus masking the signature of emerging bubbles and, second, they lack thermodynamic consistency. Here, we present two grid-based methods, the M-method and the V-method, to detect bubbles in metastable water specifically designed to address these shortcomings. The M-method incorporates information about neighbouring grid cells to distinguish between liquid- and vapour-like cells, which allows for a very sensitive detection of small bubbles and high spatial resolution of the detected bubbles. The V-method is calibrated such that its estimates for the bubble volume correspond to the average change in system volume and are thus thermodynamically consistent. Both methods are computationally inexpensive such that they can be used in molecular dynamics and Monte Carlo simulations of cavitation. We illustrate them by computing the free energy barrier and the size of the critical bubble for cavitation in water at negative pressure. PMID:25399176

González, Miguel A; Menzl, Georg; Aragones, Juan L; Geiger, Philipp; Caupin, Frederic; Abascal, Jose L F; Dellago, Christoph; Valeriani, Chantal

2014-11-14

231

Processing of Microalgae: Acoustic Cavitation and Hydrothermal Conversion  

NASA Astrophysics Data System (ADS)

The production of energy dense fuels from renewable algal biomass feedstocks -- if sustainably developed at a sufficiently large scale -- may reduce the consumption of petroleum from fossil fuels and provide many environmental benefits. Achieving economic feasibility has several technical engineering challenges that arise from dilute concentration of growing algae in aqueous media, small cell sizes, and durable cell walls. For microalgae to be a sustainable source of biofuels and co-products, efficient fractionation and conversion of the cellular contents is necessary. Research was carried out to address two processing options for efficient microalgae biofuel production: 1. Ultrasonic cavitation for cell disruption and 2. Hydrothermal conversion of a model algal triglyceride. 1. Ultrasonic cell disruption, which relies on cavitating bubbles in the suspension to produce damaging shock waves, was investigated experimentally over a range of concentrations and species types. A few seconds of high intensity sonication at fixed frequency yielded significant cell disruption, even for the more durable cells. At longer exposure times, effectiveness was seen to decline and was attributed, using acoustic measurements, to ultrasonic power attenuation in the ensuing cloud of cavitating bubbles. Processing at higher cell concentrations slowed cell disintegration marginally, but increased the effectiveness of dissipating ultrasonic energy. A theoretical study effectively predicted optimal conditions for a variety of parameters that were inaccessible in this experimental investigation. In that study, single bubble collapse was modeled to identify operating conditions that would increase cavitation, and thus cell disruption. Simulations were conducted by varying frequency and pressure amplitude of the ultrasound wave, and initial bubble size. The simulation results indicated that low frequency, high sound wave amplitudes, and small initial bubble size generate the highest shock wave pressures. 2. Hydrolysis of a pure model triglyceride compound was experimentally examined for the first time at hydrothermal conditions -- from 225 to 300°C. Lipid product composition assessed by GC-FID was compared to previous studies with mixed vegetable oils and used to develop a kinetic model for this oil phase reaction.

Greenly, Justin Michael

232

Freezing of Xylem Sap Without Cavitation  

PubMed Central

Freezing of stem sections and entire twigs of hemlock (Tsuga canadensis) has been demonstrated to occur without increasing the resistance to the movement of water through the frozen part after rewarming. This was interpreted to mean that freezing did not produce cavitation in the xylem sap even though A) the sap was unquestionably frozen; B) it contained dissolved gases; and C) it was under tension before freezing and after. Freezing stem sections of some other evergreen gymnosperms during the summer again produced no evidence for cavitation of the xylem sap. On the other hand, freezing stem sections of some angiosperms invariably increased the resistance to sap flow leading to wilting and death in a few hours when the sap tension was at normal daytime values at the time of freezing. These results were interpreted to mean that the bordered pits on the tracheids of gymnosperms function to isolate the freezing sap in each tracheid so that the expansion of water upon freezing not only eliminates any existing tension but also develops positive pressure in the sap. Dissolved gases frozen out of solution may then be redissolved under this positive pressure as melting occurs. As the bubbles are reduced in size by this ice pressure developed in an isolated tracheid, further pressure is applied by the surface tension of the water against air. If the bubbles are redissolved or are reduced to sufficient small size by the time the tension returns to the sap as the last ice crystals melt, then the internal pressure from surface tension in any existing small bubbles may exceed the hydrostatic tension of the melted sap and the bubbles cannot expand and will continue to dissolve. PMID:16656485

Hammel, H. T.

1967-01-01

233

Cavitation guide for control valves  

SciTech Connect

This guide teaches the basic fundamentals of cavitation to provide the reader with an understanding of what causes cavitation, when it occurs, and the potential problems cavitation can cause to a valve and piping system. The document provides guidelines for understanding how to reduce the cavitation and/or select control valves for a cavitating system. The guide provides a method for predicting the cavitation intensity of control valves, and how the effect of cavitation on a system will vary with valve type, valve function, valve size, operating pressure, duration of operation and details of the piping installation. The guide defines six cavitation limits identifying cavitation intensities ranging from inception to the maximum intensity possible. The intensity of the cavitation at each limit Is described, including a brief discussion of how each level of cavitation influences the valve and system. Examples are included to demonstrate how to apply the method, including making both size and pressure scale effects corrections. Methods of controlling cavitation are discussed providing information on various techniques which can be used to design a new system or modify an existing one so it can operate at a desired level of cavitation.

Tullis, J.P. [Tullis Engineering Consultants, Logan, UT (United States)

1993-04-01

234

Investigation of a Method to Reduce Cavitation in Diesel Engine Bearings  

NASA Technical Reports Server (NTRS)

Sonoluminescence is the effect of producing light from sound and occurs when a gas bubble is trapped in a fluid filled cavity and is forced to collapse under a barrage of sound waves. Frenzel and Schultes discovered this phenomenon in 1934 while exposing acoustic waves to photographic plates. This effect was not well understood until 1988 when Crum and Gaitan discovered the necessary conditions for producing single bubble sonoluminescence in the laboratory. The luminescence is a result of the bubble violently collapsing from sound waves and this shares a close association with vibratory cavitation. Cavitation erosion is known to cause damage to rotational machinery when the collapse is near to surfaces due to the high pressures associated with bubble collapse. With these high pressures and temperatures there is a considerable amount of damage to the outside layer of a bearing, thereby, reducing its useful life. An experiment was constructed to generate sonoluminescence in the laboratory in order to obtain a greater understanding of this phenomenon and its association with bubble cavitation. Most of the research was done to investigate how to obtain single bubble sonoluminescence under different conditions and to determine how to detect it. Success in this has inspired several theories on how to use the methods for generating sonoluminescence to control cavitation in fluids under industrial conditions.

Keith, Theo G., Jr.; Honaker, Robert W.

1998-01-01

235

A detector for monitoring the onset of cavitation during therapy-level measurements of ultrasonic power  

NASA Astrophysics Data System (ADS)

Acoustic cavitation occurring in the water path between a transducer and the target of a radiation force balance can provide a significant source of error during measurements of ultrasonic power. These problems can be particularly acute at physiotherapy levels (>1 W), and low frequencies (leq 1 MHz). The cavitating bubbles can absorb and scatter incident ultrasound, leading to an underestimate in the measured power. For these reasons, International Specification standards demand the use of degassed water. This imposes requirements that may actually be difficult to meet, for example, in the case of hospitals. Also, initially degassed water will rapidly re-gas, increasing the likelihood of cavitation occurring. For these reasons, NPL has developed a device that monitors acoustic emissions generated by bubble activity, for detecting the onset of cavitation during power measurements. A commercially available needle hydrophone is used to detect these emissions. The acoustic signals are then monitored using a Cavitation Detector (CD) unit, comprising an analogue electrical filter that may be tuned to detect frequency components generated by cavitating bubbles, and which provides an indication of when the measured level exceeds a pre-defined threshold. This paper describes studies to establish a suitable detection scheme, the principles of operation of the CD unit, and the performance tests carried out with a range of propagation media.

Hodnett, M.; Zeqiri, B.

2004-01-01

236

A Study of Cavitation Activity in Ex vivo Tissue Exposed to High Intensity Focused Ultrasound  

NASA Astrophysics Data System (ADS)

Cavitation is often avoided in Focused Ultrasound Surgery (FUS or HIFU) because it can render lesion formation unpredictable. However, cavitation is known to enhance heating. Emissions used as indicators for cavitation activity in ex vivo tissue are not fully understood. This study investigates a wide range of simultaneous acoustic emissions and other potential indicators of cavitation activity. A high frequency (?50MHz) data acquisition system is used to detect cavitation ex vivo. The passive cavitation detector (PCD) used is a broadband (0.1-10MHz) cavitation sensor. Its broadband nature allows simultaneous measurement of subharmonics, superharmonics and broadband emissions, all potential indicators of either inertial or both types of cavitation. The electrical impedance change of the transducer (1.69MHz, 15cm focal length, 1.79f-number), caused by backscattered ultrasound, has been monitored. Low frequency acoustic signals (<100kHz) have been recorded using a hydrophone (Reson TC4013, 1Hz-170kHz). The ultimate aim of this work is to investigate the possibility of detecting cavitation signals from HIFU during clinical treatments. Results of monitoring multiple cavitation signals during ex vivo HIFU exposure are presented. The relationship between impedance change and superharmonic emissions, indicating discrete acoustic emissions or scattering of ultrasound from bubbles, are discussed. Artefacts in B-mode ultrasound scans taken during HIFU exposures have been seen to correlate with impedance change and acoustic emissions. This is still under investigation. Cavitation thresholds in degassed water and ex vivo tissue have been investigated. This work paves the way for investigation of the enhancement of lesion formation from HIFU exposures by exploiting cavitation activity.

McLaughlan, James; Rivens, Ian; ter Haar, Gail

2007-05-01

237

Parametric study of acoustically-driven microbubble cavitations in a sonochemical reactor.  

PubMed

The bubble cavitation along a solid wall is investigated with a three-dimensional model based on the indirect boundary element method. Kinetic energy and Kelvin impulse are calculated in order to quantify the strength of cavitation. The influences of acoustic wave amplitude and frequency and liquid properties on the strength of cavitation are investigated. This study was carried out in order to better understand the relation between microscale processes and macroscale parameters in a sonochemical reactor used for impregnation of fabrics with nanoparticles. PMID:23958355

Fu, Zhiwei; Popov, Viktor

2014-01-01

238

Shock-induced collapse of a bubble inside a deformable vessel  

PubMed Central

Shockwave lithotripsy repeatedly focuses shockwaves on kidney stones to induce their fracture, partially through cavitation erosion. A typical side effect of the procedure is hemorrhage, which is potentially the result of the growth and collapse of bubbles inside blood vessels. To identify the mechanisms by which shock-induced collapse could lead to the onset of injury, we study an idealized problem involving a preexisting bubble in a deformable vessel. We utilize a high-order accurate, shock- and interface-capturing, finite-volume scheme and simulate the three-dimensional shock-induced collapse of an air bubble immersed in a cylindrical water column which is embedded in a gelatin/water mixture. The mixture is a soft tissue simulant, 10% gelatin by weight, and is modeled by the stiffened gas equation of state. The bubble dynamics of this model configuration are characterized by the collapse of the bubble and its subsequent jetting in the direction of the propagation of the shockwave. The vessel wall, which is defined by the material interface between the water and gelatin/water mixture, is invaginated by the collapse and distended by the impact of the jet. The present results show that the highest measured pressures and deformations occur when the volumetric confinement of the bubble is strongest, the bubble is nearest the vessel wall and/or the angle of incidence of the shockwave reduces the distance between the jet tip and the nearest vessel surface. For a particular case considered, the 40 MPa shockwave utilized in this study to collapse the bubble generated a vessel wall pressure of almost 450 MPa and produced both an invagination and distention of nearly 50% of the initial vessel radius on a 𝒪(10) ns timescale. These results are indicative of the significant potential of shock-induced collapse to contribute to the injury of blood vessels in shockwave lithotripsy. PMID:24015027

Coralic, Vedran; Colonius, Tim

2013-01-01

239

Formation conditions for bubble suspensions upon shock-wave loading of liquids  

Microsoft Academic Search

The conditions of development of bubble cavitation in liquid media upon shock-wave loading are found. It is s shown that,\\u000a for the development of an unbounded cavitation, the bubbles should grow to certain critical sizes sufficient for their transition\\u000a to a nonequilibrium state owing to the elastic energy transferred by a rarefaction wave to a liquid sample (at the stage

N. A. Stebnovskii

2000-01-01

240

Re-entrant jet formation and shock emission in non-spherical bubble collapse  

Microsoft Academic Search

The collapse of cavitation bubbles near a surface is a significant contributor to cavitation damage. In the present work, a high-order-accurate, quasi-conservative, interface- and shock-capturing scheme is used to simulate the collapse of a single air bubble numerically. The method allows non-spherical deformations of the interface (re-entrant jet formation) and shockwave generation and propagation. Axisymmetric Rayleigh collapse (RC) and shock-induced

Eric Johnsen; Tim Colonius

2007-01-01

241

The Influence of Dissolved Carbon Dioxide on Cavitation Intensity in Ultrasound Cleaning Systems  

NASA Astrophysics Data System (ADS)

A study is made of the effect of dissolved CO2 on cavitation inception and activity in an ultrasound system with a sound frequency of 928 kHz. It is shown that measurable cavitation activity is completely absent at moderate acoustic power densities (?1.7 W cm-2) when only CO2 is dissolved in ultra pure water. It is suggested that the enhanced stability of CO2 bubbles against coalescence might be the origin of the delayed cavitation inception when compared to other dissolved gases. A combination of dissolved O2 and CO2 can lead to a measurable cavitation activity at an acoustic power of 420 mW cm-2, but an increase of the dissolved CO2 level reduces, in general, the observed cavitation activity. In order to compare results with different dissolved gas concentrations, measurements are performed with acoustic pulses and the pulse off time is varied. An optimal pulse-off time exists, where a maximum of cavitation activity is observed. However, the pulse-off time interval with enhanced cavitation activity is narrowed with increasing dissolved CO2 concentrations. Again, a decrease in bubble coalescence might explain the narrowing of the “enhancement peak”.

Brems, Steven; Hauptmann, Marc; Camerotto, Elisabeth; Pacco, Antoine; Struyf, Herbert; Mertens, Paul; Gottschalk, Christiane; De Gendt, Stefan

2013-06-01

242

Creep cavitation in 304 stainless steel  

Microsoft Academic Search

Creep cavitation in 304 stainless steel at 0.5 T\\/sub m\\/ was investigated. Two specially developed techniques were used to study the nucleation and growth of grain-boundary cavities. It was found that cavities nucleated heterogeneously throughout the creep history and those observed were well in their growth stage. Comparison of these observations with the theory for cavity nucleation requires that a

I. W. Chen; A. S. Argon

1981-01-01

243

Amyloid fibril disruption by ultrasonic cavitation: nonequilibrium molecular dynamics simulations.  

PubMed

We describe the disruption of amyloid fibrils of Alzheimer's amyloid-? peptides by ultrasonic cavitation. For this purpose, we performed nonequilibrium all-atom molecular dynamics simulations with sinusoidal pressure and visualized the process with movies. When the pressure is negative, a bubble is formed, usually at hydrophobic residues in the transmembrane region. Most ?-strands maintain their secondary structures in the bubble. When the pressure becomes positive, the bubble collapses, and water molecules crash against the hydrophilic residues in the nontransmembrane region to disrupt the amyloid. Shorter amyloids require longer sonication times for disruption because they do not have enough hydrophobic residues to serve as a nucleus to form a bubble. These results agree with experiments in which monodispersed amyloid fibrils were obtained by ultrasonication. PMID:24987794

Okumura, Hisashi; Itoh, Satoru G

2014-07-30

244

Tumour-associated macrophages targeted transfection with NF-?B decoy/mannose-modified bubble lipoplexes inhibits tumour growth in tumour-bearing mice.  

PubMed

Tumour-associated macrophages (TAM) exhibit an M2 phenotype that promotes tumour progression, and conversion of M2 TAM toward a tumouricidal M1 phenotype is a promising anti-cancer therapy. As NF-?B is a key regulator of macrophage polarization, we developed an in vivo TAM-targeting delivery system that combines mannose-modified bubble liposomes/NF-?B decoy complexes (Man-PEG bubble lipoplexes) and ultrasound (US) exposure. We investigated the effects of NF-?B decoy transfection on TAM phenotype in solid tumour-bearing mice. Post-transfection tumour growth and survival rates were also recorded. Th2 cytokine (IL-10) level in TAM was significantly lower by NF-?B decoy transfection using Man-PEG bubble lipoplexes and US exposure, while Th1 cytokine levels (IL-1?, TNF-? and IL-6) were significantly higher when compared with controls. In addition, mRNA levels of vascular endothelial growth factor, matrix metalloproteinase-9 and arginase were significantly lower in TAM post-NF-?B decoy transfection. Importantly, TAM-targeted NF-?B decoy transfection inhibited tumour growth and prolonged survival rates in mice. Therefore, TAM-targeted NF-?B decoy transfection using Man-PEG bubble lipoplexes and US exposure may be an effective approach for anti-cancer therapy based on TAM phenotypic conversion from M2 toward M1. PMID:24579693

Kono, Yusuke; Kawakami, Shigeru; Higuchi, Yuriko; Maruyama, Kazuo; Yamashita, Fumiyoshi; Hashida, Mitsuru

2014-06-01

245

Interaction of Two Differently Sized Bubbles in a Free Field  

NASA Astrophysics Data System (ADS)

The interaction between two different sized (spark created, non-equilibrium) bubbles is studied by using high speed photography. The bubble size ranges from 2 to 7 mm. The experimental results are compared to that of the similar sized bubbles reported in the literature. Interestingly, all the four major behaviors of bubble-bubble interactions (i.e. 'bubble-collapsed' induced liquid jets directed away from each other, liquid jets directed towards each other, bubble coalescence and the 'catapult' effect) are observed which bear much similarity to that found for similar sized bubbles' interaction. The main parameters studied/varied are the size of the bubbles, the dimensionless separation distance and the phase difference between the two bubbles. The results obtained are consistent with the cases of similar sized bubbles reported in the literature, with each type of behavior occupying a distinct region in the graphical plot. This indicates that the results for the (special) similar sized bubbles can be generalized to cases with different sized bubbles. Many of the real life applications such as cavitations corrosions often involve bubbles with significant size difference, thus the present findings are useful in predicting the behavior of multiple bubbles in many situations.

Chew, Lup Wai; Khoo, Boo Cheong; Klaseboer, Evert; Ohl, Siew-Wan

246

Power spectrum of fluctuation for ultrasonic cavitation process in glycerin  

Microsoft Academic Search

Experiments were carried out on ultrasonic cavitation in glycerin. The zone near the emitter has a structure from interacting\\u000a gas-vapor bubbles; this structure takes the form of fractal clusters. The photometry of passed laser emission was the tool\\u000a for studying dynamics of fluctuations. In transitive mode, the power spectrum of fluctuation varies by the law inversely proportional\\u000a to frequency. Distributions

V. N. Skokov; V. P. Koverda; A. V. Reshetnikov; A. V. Vinogradov

2007-01-01

247

An experimental investigation of acoustic cavitation in gaseous liquids  

NASA Astrophysics Data System (ADS)

High amplitude radial pulsations of a single bubble in several glycerine and water mixtures were observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa at 21 to 25 kHz. Sonoluminescence, a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring once every acoustic period. These emissions could be seen to originate at the geometric center of the bubble when observed through a microscope. It was observed that the light emissions occurred simultaneously with the bubble collapse. Using a laser scattering technique, experimental radius-time curves were obtained which confirmed the absence of surface waves which are expected at pressure amplitudes above 100 kPa. From these radius-time curves, measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds were made and compared with several theories. The implications of this research on the current understanding of cavitation were discussed.

Gaitan, Dario F.; Crum, Lawrence A.

1990-11-01

248

A Experimental Investigation of Acoustic Cavitation in Gaseous Liquids  

NASA Astrophysics Data System (ADS)

High amplitude radial pulsations of a single gas bubble in several glycerine and water mixtures have been observed in an acoustic stationary wave system at acoustic pressure amplitudes as high as 1.5 bars. Using a laser scattering technique, radius-time curves have been obtained experimentally which confirm the absence of surface waves. Measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds have been made and compared with the theory. From these data, calculations of the internal gas temperature and pressure during the collapse have been performed. Values of at least 2,000 K and 2,000 bars have been obtained using a sophisticated model of spherically symmetric bubble dynamics. Simultaneously, sonoluminescence (SL), a phenomenon discovered in 1933 and attributed today to the high temperatures and pressures generated during the collapse of the bubbles, were observed as short light pulses occurring once every acoustic period. The light emissions can be seen to originate at the geometric center of the bubble when observed through a microscope. Also, the simultaneity of the light emissions and the collapse of the bubble has been confirmed with the aid of a photomultiplier tube. This is the first recorded observation of SL generated by a single bubble. Comparisons of the measured quantities have been made to those predicted by several models. In addition, the implications of this research on the current understanding of cavitation related phenomena such as rectified diffusion, surface wave excitation and sonoluminescence will be discussed. Some possible future experiments are suggested which could further increase our understanding of cavitation bubble dynamics.

Gaitan, Dario Felipe

1990-01-01

249

Effect of tensile stress on cavitation damage formation in mercury  

NASA Astrophysics Data System (ADS)

Cavitation erosion or so called pitting damage was investigated under tensile stress conditions in mercury. In MW-class liquid metal spallation targets, pitting damage is a critical issue to satisfy required power and/or lifetime of the target vessel. Cavitation occurs by negative pressure which is induced through pressure wave propagation due to proton beam injection. Pitting damage is formed by microjet and/or shock wave during cavitation bubble collapse. A mercury target vessel suffers tensile stress due to thermal stress or welding. In order to investigate the effect of tensile stress on pitting damage formation, cavitation erosion tests were performed using stress imposed specimens in mercury. An ultrasonic vibratory horn and electro-Magnetic IMpact Testing Machine (MIMTM) were used to vary the cavitation intensity. In the incubation period of pitting damage, damaged area was slightly increased with increasing imposed tensile stress. In the steady state period, a mean depth of erosion was increased by the tensile stress. Additionally, in order to quantitatively evaluate the effect of tensile stress, an indentation test with Vickers indenter was carried out to quasi-statically simulate the impact load. From the measurement of the diagonal length of the indent aspect ratio and hardness, it is recognized that the threshold of the deformation, i.e. pitting damage formation, was decreased by the tensile stress.

Naoe, Takashi; Kogawa, Hiroyuki; Yamaguchi, Yoshihito; Futakawa, Masatoshi

2010-03-01

250

The effects of total dissolved gas on chum salmon fry survival, growth, gas bubble disease, and seawater tolerance  

SciTech Connect

Chum salmon Oncorhynchus keta alevin developing in gravel habitats downstream of Bonneville Dam on the Columbia River are exposed to elevated levels of total dissolved gas (TDG) when water is spilled at the dam to move migrating salmon smolts downstream to the Pacific Ocean. Current water quality criteria for the management of dissolved gas in dam tailwaters were developed primarily to protect salmonid smolts and are assumed to be protective of alevin if adequate depth compensation is provided. We studied whether chum salmon alevin exposed to six levels of dissolved gas ranging from 100% to 130% TDG at three development periods between hatch and emergence (hereafter early, middle, and late stage) suffered differential mortality, growth, gas bubble disease, or seawater tolerance. Each life stage was exposed for 50 d (early stage), 29 d (middle stage), or 16 d (late stage) beginning at 13, 34, and 37 d post-hatch, respectively, through 50% emergence. The mortality for all stages from exposure to emergence was estimated to be 8% (95% confidence interval (CI) of 4% to 12%) when dissolved gas levels were between 100% and 117% TDG. Mortality significantly increased as dissolved gas levels rose above 117% TDG,; with the lethal concentration that produced 50% mortality (LC50 ) was estimated to be 128.7% TDG (95% CI of 127.2% to 130.2% TDG) in the early and middle stages. By contrast, there was no evidence that dissolved gas level significantly affected growth in any life stage except that the mean wet weight at emergence of early stage fish exposed to 130% TDG was significantly less than the modeled growth of unexposed fish. The proportion of fish afflicted with gas bubble disease increased with increasing gas concentrations and occurred most commonly in the nares and gastrointestinal tract. Early stage fish exhibited higher ratios of filament to lamellar gill chloride cells than late stage fish, and these ratios increased and decreased for early and late stage fish, respectively, as gas levels increased; however, there were no significant differences in mortality between life stages after 96 h in seawater. The study results suggest that current water quality guidelines for the management of dissolved gas appear to offer a conservative level of protection to chum salmon alevin incubating in gravel habitat downstream of Bonneville Dam.

Geist, David R.; Linley, Timothy J.; Cullinan, Valerie I.; Deng, Zhiqun

2013-02-01

251

A Study of Cavitation Erosion  

SciTech Connect

The authors performed experimental study for the purpose of the following two items from a viewpoint of cavitation erosion of a cylindrical orifice in view of a problem at the letdown orifice in PWR (Pressurized Water Reactor). 1. To get the critical cavitation parameter of the cylindrical orifice to establish the design criteria for prevention of cavitation erosion, and 2. to ascertain the erosion rate in such an eventuality that the cavitation erosion occurs with the orifice made of stainless steel with precipitation hardening (17-4-Cu hardening type stainless steel), so that we confirm the appropriateness of the design criteria. Regarding the 1. item, we carried out the cavitation tests to get the critical cavitation parameters inside and downstream of the orifice. The test results showed that the cavitation parameter at inception is independent of the length or the diameter of the orifice. Moreover, the design criteria of cavitation erosion of cylindrical orifices have been established. Regarding the 2. item, we tested the erosion rate under high-pressure conditions. The cavitation erosion actually occurred in the cylindrical orifice at the tests that was strongly resemble to the erosion occurred at the plant. It will be seldom to reproduce resemble cavitation erosion in a cylindrical orifice with the hard material used at plants. We could establish the criteria for preventing the cavitation erosion from the test results. (authors)

Hiromu Isaka [Kansai Electric Power Company (Japan); Masatsugu Tsutsumi; Tadashi Shiraishi [Mitsubishi Heavy Industries Ltd. (Japan); Hiroyuki Kobayashi [Japan Atomic Power Company (Japan)

2002-07-01

252

Regular three-dimensional bubble clusters: shape, packing and growth-rate  

E-print Network

that this is the familiar honeycomb structure. In 3D, where the problem is one of minimizing surface energy or area/V2/3. · Growth laws: how does a foam age, or coarsen, due to gas diffusion across its surfaces? The 2 of the precise geometry. In 3D, the growth law is written [7]: dV2/3 dt = 1 2 i piSi V1/3 (1) where the sum

Cox, Simon

253

Complete Inhibition Of Ultrasound Induced Cytolysis In The Presence Of Inertial Cavitation  

NASA Astrophysics Data System (ADS)

The investigation of ultrasound for biotechnological applications including non-invasive surgery (HIFU), drug/gene delivery to cells (sonoporation) or through the skin (sonophoresis) and ultrasound assisted bioreactors has focused mainly on the physical effects of ultrasound. The beneficial effects of ultrasound rely on a number of application-dependent mechanisms, and may include tissue heating, acoustic streaming or cavitation. Although acoustic cavitation is necessary in some systems, cavitation bubbles simultaneously result in uncontrollable cell damage and cytolysis. Thus, the development of a number of biotechnological uses of ultrasound has been hampered by the necessity to constrain exposure parameters in order to prevent the occurrence of acoustic cavitation or to at least limit the detrimental effects of cavitation. The current study shows that non-toxic concentrations of specific n-alkyl solutes completely inhibit ultrasound induced cytolysis of in vitro suspensions of human leukemia cells (HL-60). Protection of the whole cell population from cytolysis is achieved even under extreme ultrasound exposure conditions that result in cytolysis of 100 % of the cell population in the absence of the n-alkyl solutes. Furthermore, the n-alkyl solutes did not hinder the process of inertial cavitation. This method may allow utilization of beneficial effects of ultrasound and cavitation while protecting cells from cavitation induced cytolysis and thereby presents new possibilities for ultrasound in medicine and biology.

Sostaric, Joe Z.; Miyoshi, Norio; Riesz, Peter; De Graff, William G.; Mitchell, James B.

2006-05-01

254

Recalcitrant bubbles  

PubMed Central

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in ‘anomalous' mixtures. Unlike ‘ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just ‘downstream' of the minimum in surface tension. The exponential trend for bubbles in ‘anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles). PMID:24740256

Shanahan, Martin E. R.; Sefiane, Khellil

2014-01-01

255

DNA denaturation bubbles at criticality  

E-print Network

The equilibrium statistical properties of DNA denaturation bubbles are examined in detail within the framework of the Peyrard-Bishop-Dauxois model. Bubble formation in homogeneous DNA is found to depend crucially on the presence of nonlinear base-stacking interactions. Small bubbles extending over less than 10 base pairs are associated with much larger free energies of formation per site than larger bubbles. As the critical temperature is approached, the free energy associated with further bubble growth becomes vanishingly small. An analysis of average displacement profiles of bubbles of varying sizes at different temperatures reveals almost identical scaled shapes in the absence of nonlinear stacking; nonlinear stacking leads to distinct scaled shapes of large and small bubbles.

Theodorakopoulos, Nikos

2008-01-01

256

CAVITATION AND CETACEAN  

Microsoft Academic Search

Bubbles are the most acoustically active naturally occurring entities in the ocean, and cetaceans are the most intelligent. Having evolved over tens of millions of years to cope with the underwater acoustic environment, cetaceans may have developed techniques from which we could learn. This paper outlines some of the possible interactions, ranging from the exploitation of acoustics in bubble nets

Timothy G. Leighton

257

Bubble Puzzles  

NASA Astrophysics Data System (ADS)

Bubbles are fascinating. With their ubiquitous occurrence in a multitude of fluid systems bubbles occupy a very important place in contemporary science and technology. In many applications, bubble control is crucial. I will demonstrate that bubble nucleation at surfaces, which always has been associated with randomness, can be perfectly controlled both in space and time. This new technique allows to quantitatively study bubble-bubble and bubble-surface interaction and reveals a shielding effect in bubble clusters [1]. -- In a second example for the importance of bubble control I will discuss their disturbing effect in piezo-acoustic ink-jet printing: I will show how bubbles are entrained, grow by rectified diffusion, and finally seriously disturb the jetting process by counteracting the pressure build-up at the nozzle [2]. [1] N. Bremond, M. Arora, C. D. Ohl, and D. Lohse, Phys. Rev. Lett. 96, 224501 (2006). [2] J. de Jong, H. Reinten, M. van den Berg, H. Wijshoff, M. Versluis, G. de Bruin, and D. Lohse, J. Acoust. Soc. Am., (August 2006).

Lohse, Detlef

2006-11-01

258

Correlation between simulations and cavitation-induced erosion damage in Spallation Neutron Source target modules after operation  

SciTech Connect

An explicit finite element (FE) technique developed for estimating dynamic strain in the Spallation Neutron Source (SNS) mercury target module vessel is now providing insight into cavitation damage patterns observed in used targets. The technique uses an empirically developed material model for the mercury that describes liquid-like volumetric stiffness combined with a tensile pressure cut-off limit that approximates cavitation. The longest period each point in the mercury is at the tensile cut-off threshold is denoted its saturation time. Now, the pattern of saturation time can be obtained from these simulations and is being positively correlated with observed damage patterns and is interpreted as a qualitative measure of damage potential. Saturation time has been advocated by collaborators at J-Parc as a factor in predicting bubble nuclei growth and collapse intensity. The larger the ratio of maximum bubble size to nucleus, the greater the bubble collapse intensity to be expected; longer saturation times result in greater ratios. With the recent development of a user subroutine for the FE solver saturation time is now provided over the entire mercury domain. Its pattern agrees with spots of damage seen above and below the beam axis on the SNS inner vessel beam window and elsewhere. The other simulation result being compared to observed damage patterns is mercury velocity at the wall. Related R&D has provided evidence for the damage mitigation that higher wall velocity provides. In comparison to observations in SNS targets, inverse correlation of high velocity to damage is seen. In effect, it is the combination of the patterns of saturation time and low velocity that seems to match actual damage patterns.

Riemer, Bernie [ORNL] [ORNL; McClintock, David A [ORNL] [ORNL; Kaminskas, Saulius [ORNL] [ORNL; Abdou, Ashraf A [ORNL] [ORNL

2014-01-01

259

Cavitation behavior observed in three monoleaflet mechanical heart valves under accelerated testing conditions.  

PubMed

Accelerated testing provides a substantial amount of data on mechanical heart valve durability in a short period of time, but such conditions may not accurately reflect in vivo performance. Cavitation, which occurs during mechanical heart valve closure when local flow field pressure decreases below vapor pressure, is thought to play a role in valve damage under accelerated conditions. The underlying flow dynamics and mechanisms behind cavitation bubble formation are poorly understood. Under physiologic conditions, random perivalvular cavitation is difficult to capture. We applied accelerated testing at a pulse rate of 600 bpm and transvalvular pressure of 120 mm Hg, with synchronized videographs and high-frequency pressure measurements, to study cavitation of the Medtronic Hall Standard (MHS), Medtronic Hall D-16 (MHD), and Omni Carbon (OC) valves. Results showed cavitation bubbles between 340 and 360 micros after leaflet/housing impact of the MHS, MHD, and OC valves, intensified by significant leaflet rebound. Squeeze flow, Venturi, and water hammer effects each contributed to cavitation, depending on valve design. PMID:18356649

Lo, Chi-Wen; Liu, Jia-Shing; Li, Chi-Pei; Lu, Po-Chien; Hwang, Ned H

2008-01-01

260

A review and assessment of hydrodynamic cavitation as a technology for the future.  

PubMed

In the present work, the current status of the hydrodynamic cavitation reactors has been reviewed discussing the bubble dynamics analysis, optimum design considerations, design correlations for cavitational intensity (in terms of collapse pressure)/cavitational yield and different successful chemical synthesis applications clearly illustrating the utility of these types of reactors. The theoretical discussion based on the modeling of the bubble dynamics equations aims at understanding the design information related to the dependency of the cavitational intensity on the operating parameters and recommendations have been made for the choice of the optimized conditions of operating parameters. The design information based on the theoretical analysis has also been supported with some experimental illustrations concentrating on the chemical synthesis applications. Assessment of the hydrodynamic cavitation reactors and comparison with the sonochemical reactors has been done by citing the different industrially important reactions (oxidation of toluene, o-xylene, m-xylene, p-xylene, mesitylene, o-nitrotoluene, p-nitrotoluene, m-nitrotoluene, o-chlorotoluene and p-chlorotoulene, and trans-esterification reaction i.e., synthesis of bio-diesel). Some recommendations have also been made for the future work to be carried out as well as the choice of the operating conditions for realizing the dream of industrial scale applications of the cavitational reactors. PMID:15474948

Gogate, Parag R; Pandit, Aniruddha B

2005-01-01

261

Enhancing gas-liquid mass transfer rates in non-newtonian fermentations by confining mycelial growth to microbeads in a bubble column  

Microsoft Academic Search

The performance of a penicillin fermentation was assessed in a laboratory-scale bubble column fermentor, with mycelial growth confined to the pore matrix of celite beads. Final cell densities of 29 g\\/L and penicillin titres of 5.5 g\\/L were obtained in the confined cell cultures. In comparison, cultures of free mycelial cells grown in the absence of beads experienced dissolved oxygen

K. Gbewonyo; D. I. C. Wang

1983-01-01

262

Correlation between bubble repulsion and metal properties  

NASA Astrophysics Data System (ADS)

One way to protect a parent metal from cavitation impact is by rejecting the bubble from the solid boundary. The repulsion of a bubble can be achieved by employing a low impedance material as a coating. We have carried out an experimental study by coupling the low impedance material with different types of metal. In the case of surface roughness effect studies, abrasive papers were employed. The bubble repulsion induced by focused laser light was captured using a CCD video camera which was interfaced with an image processing system. The attained results show that the repulsion of the bubble is independent of the physical properties of the parent metal but inversely proportional to the surface roughness.

Sekak, Khairunnadim Ahmad; Bidin, Noriah

2000-07-01

263

Luminescence from Tube-Arrest Bubbles in Pure Glycerin  

NASA Astrophysics Data System (ADS)

Single transient cavitation bubble with luminescence has been generated in pure glycerin by using the `tube arrest' method. The analyses of high-speed photograph and light emission data suggest that the light emission would be a single bubble sonoluminescence. The luminescence pulse width is observed to vary from sub-nanosecond to about 30 ns. The width and intensity of luminescence pulses increases with the height of the liquid column height and decreases with the liquid temperature.

Chen, Qi-Dai; Wang, Long

2004-09-01

264

Model test and CFD calculation of a cavitating bulb turbine  

NASA Astrophysics Data System (ADS)

The flow in a horizontal shaft bulb turbine is calculated as a two-phase flow with a commercial Computational Fluid Dynamics (CFD-)-code including cavitation model. The results are compared with experimental results achieved at a closed loop test rig for model turbines. On the model test rig, for a certain operating point (i.e. volume flow, net head, blade angle, guide vane opening) the pressure behind the turbine is lowered (i.e. the Thoma-coefficient ? is lowered) and the efficiency of the turbine is recorded. The measured values can be depicted in a so-called ?-break curve or ?- ?-diagram. Usually, the efficiency is independent of the Thoma-coefficient up to a certain value. When lowering the Thoma-coefficient below this value the efficiency will drop rapidly. Visual observations of the different cavitation conditions complete the experiment. In analogy, several calculations are done for different Thoma-coefficients ?and the corresponding hydraulic losses of the runner are evaluated quantitatively. For a low ?-value showing in the experiment significant efficiency loss, the the change of volume flow in the experiment was simulated. Besides, the fraction of water vapour as an indication of the size of the cavitation cavity is analyzed qualitatively. The experimentally and the numerically obtained results are compared and show a good agreement. Especially the drop in efficiency can be calculated with satisfying accuracy. This drop in efficiency is of high practical importance since it is one criterion to determine the admissible cavitation in a bulb-turbine. The visual impression of the cavitation in the CFD-analysis is well in accordance with the observed cavitation bubbles recorded on sketches and/or photographs.

Necker, J.; Aschenbrenner, T.

2010-08-01

265

Acoustically driven cavitation cluster collapse in planar geometry Ivan van der Kroon,1  

E-print Network

, double, and complex configurations of cavitation bubbles are obtained by shaping a pulsed laser beam, arrangements of cavities were cut into a layer of gelatin and were excited with a single shock wave. Under these high pressures gelatin be- comes liquidlike, which allowed studying the collapse of the cavities

Ohl, Claus-Dieter

266

Bounds of cavitation inception in a creeping flow between eccentric cylinders rotating with a small minimum gap  

NASA Astrophysics Data System (ADS)

Bounds of cavitation inception are experimentally determined in a creeping flow between eccentric cylinders, the inner one being static and the outer rotating at a constant angular velocity, ?. The geometric configuration is additionally specified by a small minimum gap between cylinders, H, as compared with the radii of the inner and outer cylinders. For some values H and ?, cavitation bubbles are observed, which are collected on the surface of the inner cylinder and equally distributed over the line parallel to its axis near the downstream minimum gap position. Cavitation occurs for the parameters {H,?} within a region bounded on the right by the cavitation inception curve that passes through the plane origin and cannot exceed the asymptotic threshold value of the minimum gap, Ha, in whose vicinity cavitation may occur at H < Ha only for high angular rotation velocities.

Monakhov, A. A.; Chernyavski, V. M.; Shtemler, Yu.

2013-09-01

267

Mechanisms of mechanical heart valve cavitation in an electrohydraulic total artificial heart.  

PubMed

Until now, we have estimated cavitation for mechanical heart valves (MHV) mounted in an electrohydraulic total artificial heart (EHTAH) with tap water as a working fluid. However, tap water at room temperature is not a proper substitute for blood at 37 degrees C. We therefore investigated MHV cavitation using a glycerin solution that was identical in viscosity and vapor pressure to blood at body temperature. In this study, six different kinds of monoleaflet and bileaflet valves were mounted in the mitral position in an EHTAH, and we investigated the mechanisms for MHV cavitation. The valve closing velocity, pressure drop measurements, and a high-speed video camera were used to investigate the mechanism for MHV cavitation and to select the best MHV for our EHTAH. The closing velocity of the bileaflet valves was slower than that of the monoleaflet valves. Cavitation bubbles were concentrated on the edge of the valve stop and along the leaflet tip. It was established that squeeze flow holds the key to MHV cavitation in our study. Cavitation intensity increased with an increase in the valve closing velocity and the valve stop area. With regard to squeeze flow, the Björk-Shiley valve, because it is associated with slow squeeze flow, and the bileaflet valve with low valve closing velocity and small valve stop areas are better able to prevent blood cell damage than the monoleaflet valves. PMID:15968949

Lee, Hwansung; Taenaka, Yoshiyuki; Kitamura, Soichiro

2005-01-01

268

CFD analysis of unsteady cavitation phenomena in multistage pump with inducer  

NASA Astrophysics Data System (ADS)

This paper presents the numerical simulation of the cavitating flow phenomena in the suction part of a radial-flow multistage water pump with a high rotational speed. The pump is equipped with an inducer. Besides the usual focus on the cavitation inception or the drop of the pump total head this CFD analysis also studies the possibility of the cavitation surge and attempts to quantify the risk of cavitation erosion for different flow conditions. The ANSYS CFX commercial CFD package was used to solve the URANS equations coupled with the Rayleigh-Plesset Model. The SST-SAS turbulence model was employed to capture unsteady phenomena inside the pump. The model for the prediction of the cavitation erosion risk is based on coupling the CFD analysis of 3D turbulent flow with the analysis of the dynamics of bubbles travelling along selected trajectories using the full Rayleigh-Plesset equation. The model assumes that the water at the pump inlet contains a known number of nuclei with a known size distribution. The erosion potential (or aggressiveness) of the collapse is estimated from the energy dissipated during the collapse. The presented CFD analysis has provided a map of regions endangered by cavitation erosion. The cavitation instability in the backflow vortices has been detected at 60% of the optimal flow coefficient close to the NPSHr value.

Sedlá?, M.; Zima, P.; Bajorek, M.; Krátký, T.

2012-11-01

269

Analysis of cavitation behaviour in a centrifugal pump  

NASA Astrophysics Data System (ADS)

Cavitation is a well-known problem in centrifugal pumps, causing serious damage and substantial head losses. However, the reason for the sudden head drop in cavitation curves is not fully understood. In this paper, the transient three-dimensional cavitating flow field in a centrifugal pump was calculated using RNG k-? turbulence model and Rayleigh Plesset cavitation model. The NPSH-H curve and the cavitation development in the whole passage were predicted. The blade loading and energy transfer are analyzed for various cavitation conditions. The results show that the existing of the cavities changes the load distribution on blades. With the decrease of NPSH the loads on blades tend to increases in the rear part but decreases in the front part. If NPSH is not so low, sometimes the overall torque may increase slightly, thus the head may also increase slightly. But if the NPSH become low and reach a threshold value, the overall torque will also decrease. At the same time, the energy dissipation in the vortices increases greatly because of the growth of the cavities. These two reasons make the head drop rapidly.

He, M.; Fu, L. P.; Zhou, L. J.; Guo, Q.; Wang, Z. W.

2012-11-01

270

Photodisruptive laser nucleation of ultrasonic cavitation for biomedical applications.  

PubMed

Pulses of high intensity laser light, when focused into transparent materials, may produce localized electron-ion plasmas through optical breakdown. By simultaneously incorporating the resulting volume of vaporized material within the focal volume of a high intensity ultrasound source, the photodisruption (1.05 microm wavelength) void served as a nucleation site for ultrasonic cavitation. Dilute suspensions of canine erythrocytes in phosphate buffered saline were exposed in a flow-through exposure chamber and the percentage of lysed cells was used as a measure of the biologically effective cavitation activity produced in the chamber. Brief (about 30 micros) acoustic emissions were detected from the photodisruption alone (indicating laser nucleation of bubbles), but the cell lysis produced was undetectable against the background. However, combined exposure greatly increased both the duration of the acoustic emissions (up to 1.5 ms) and the amount of cell lysis above an ultrasonic pressure amplitude threshold of about 4.3 MPa at 2.5 MHz. The amount of cell lysis (sometimes approaching 100%) increased with increasing ultrasonic intensity, laser pulse energy and laser PRF. Addition of 5% serum albumin enhanced the effect, apparently by stabilizing bubbles and nuclei. Photodisruptive laser nucleation of ultrasonic cavitation can provide controlled and synergistic enhancement of bioeffects. PMID:11516327

Miller, D L; Spooner, G J; Williams, A R

2001-07-01

271

The role of cavitational activity in fragmentation processes by lithotripters.  

PubMed

The role of cavitation during shock wave exposure was poorly understood until now. Cavitational activity produces severe damage to nearby surfaces due to multiple high-speed liquid jets resulting from bubble collapse. These jet impacts can be made visible by microscopy. For investigating the presence of cavitational processes by shock waves outside and even inside of targets, we have performed the following experiments. Natural gallstones and artificial targets were examined microscopically with regard to the effects of shock pulses. Scanning electron and light microscopical investigations revealed regularly typical and uniform microjet impacts within the fissures and split lines. Since these experiments are the continuation of high-speed films of 10,000 frames/s of shock wave actions on targets, it is most likely that the shock wave produces at first split lines through the stone. Then liquid occupies these cracks. But the following shock waves create within these liquid-filled fissures cavitation and, therefore, cause the disintegration of the targets. It now becomes understandable why biliary lithotripsy is less effective than renal lithotripsy: bile fluid is a high-viscous liquid and, therefore, hinders the disintegration of stones more than low-viscous urine. Intervals between the application of shock waves in biliary lithotripsy, therefore, should improve the treatment results. PMID:10147666

Sass, W; Dreyer, H P; Kettermann, S; Seifert, J

1992-07-01

272

Enhancing gas-liquid mass transfer rates in non-newtonian fermentations by confining mycelial growth to microbeads in a bubble column  

SciTech Connect

The performance of a penicillin fermentation was assessed in a laboratory-scale bubble column fermentor, with mycelial growth confined to the pore matrix of celite beads. Final cell densities of 29 g/L and penicillin titres of 5.5 g/L were obtained in the confined cell cultures. In comparison, cultures of free mycelial cells grown in the absence of beads experienced dissolved oxygen limitations in the bubble column, giving only 17 g/L final cell concentrations with equally low penicillin titres of 2 g/L. The better performance of the confined cell cultures was attributed to enhanced gas liquid mass transfer rates, with mass transfer coefficients (k /SUB L/ a) two to three times higher than those determined in the free cell cultures. Furthermore, the confined cell cultures showed more efficient utilization of power input for mass transfer, providing up to 50% reduction in energy requirements for aeration.

Gbewonyo, K.; Wang, D.I.C.

1983-12-01

273

Three types of cavitation caused by air seeding.  

PubMed

There are different opinions of the dynamics of an air bubble entering a xylem conduit. In this paper, we present a thorough mechanical analysis and conclude that there are three types of cavitation caused by air seeding. After an air seed enters a conduit at high xylem pressure P'(1), along with the drop of the water potential, it will expand gradually to a long-shaped bubble and extend continually. This is the first type of air seeding, or the type of expanding gradually. When the xylem pressure is moderate, right after an air seed enters a conduit, it will expand first. Then, as soon as the pressure reaches a threshold the bubble will blow up to form a bubble in long shape, accompanied by acoustic (or ultra-acoustic) emission. It will extend further as xylem pressure decreases continually. This is the second type of air seeding, or the type of expanding-exploding, becoming a long-shaped bubble-lengthening by degrees. In the range of P'(1) ? - 3P(o) (P(o) is atmospheric pressure), soon after an air seed is sucked into a conduit it will explode immediately and the conduit will be full of the gas of the bubble instantly. This is the third type of air seeding, or the type of sudden exploding and filling conduit instantly. The third type is the frequent event in daily life of plant. PMID:23100258

Shen, Fanyi; Wang, Yuansheng; Cheng, Yanxia; Zhang, Li

2012-11-01

274

Cavitation instabilities in hydraulic machines  

NASA Astrophysics Data System (ADS)

Cavitation instabilities in hydraulic machines, hydro turbines and turbopump inducers, are reviewed focusing on the cause of instabilities. One-dimensional model of hydro turbine system shows that the overload surge is caused by the diffuser effect of the draft tube. Experiments show that this effect also causes the surge mode oscillations at part load. One dimensional model of a cavitating turbopump inducer shows that the mass flow gain factor, representing the cavity volume increase caused by the incidence angle increase is the cause of cavitation surge and rotating cavitation. Two dimensional model of a cavitating turbopump inducer shows that various modes of cavitation instabilities start to occur when the cavity length becomes about 65% of the blade spacing. This is caused by the interaction of the local flow near the cavity trailing edge with the leading edge of the next blade. It was shown by a 3D CFD that this is true also for real cases with tip cavitation. In all cases, it was shown that cavitation instabilities are caused by the fundamental characteristics of cavities that the cavity volume increases with the decrease of ambient pressure or the increase of the incidence angle.

Tsujimoto, Y.

2013-12-01

275

Two reference time scales for studying the dynamic cavitation of liquid films  

NASA Astrophysics Data System (ADS)

Two formulas, one for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived. By comparing these time scales with that of the dynamic operation of oil film bearings, it is concluded that the evaporation process is usually fast enough to fill the cavitation bubble with oil vapor; whereas the diffusion process is much too slow for the dissolved air to liberate itself and enter the cavitation bubble. These results imply that the formation of a two phase fluid in dynamically loaded bearings, as often reported in the literature, is caused by air entrainment. They further indicate a way to simplify the treatment of the dynamic problem of bubble evolution.

Sun, D. C.; Brewe, D. E.

1992-07-01

276

Measurements of Gas Bubble Size Distributions in Flowing Liquid Mercury  

SciTech Connect

ABSTRACT Pressure waves created in liquid mercury pulsed spallation targets have been shown to induce cavitation damage on the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, measuring such a population in mercury is difficult since it is opaque and the mercury is involved in a turbulent flow. Ultrasonic measurements have been attempted on these types of flows, but the flow noise can interfere with the measurement, and the results are unverifiable and often unrealistic. Recently, a flow loop was built and operated at Oak Ridge National Labarotory to assess the capability of various bubbler designs to deliver an adequate population of bubbles to mitigate cavitation damage. The invented diagnostic technique involves flowing the mercury with entrained gas bubbles in a steady state through a horizontal piping section with a glass-window observation port located on the top. The mercury flow is then suddenly stopped and the bubbles are allowed to settle on the glass due to buoyancy. Using a bright-field illumination and a high-speed camera, the arriving bubbles are detected and counted, and then the images can be processed to determine the bubble populations. After using this technique to collect data on each bubbler, bubble size distributions were built for the purpose of quantifying bubbler performance, allowing the selection of the best bubbler options. This paper presents the novel procedure, photographic technique, sample visual results and some example bubble size distributions. The best bubbler options were subsequently used in proton beam irradiation tests performed at the Los Alamos National Laboratory. The cavitation damage results from the irradiated test plates in contact with the mercury are available for correlation with the bubble populations. The most effective mitigating population can now be designed into prototypical geometries for implementation into an actual SNS target.

Wendel, Mark W [ORNL; Riemer, Bernie [ORNL; Abdou, Ashraf A [ORNL

2012-01-01

277

Cavitation-resistant inducer  

DOEpatents

An improvement in an inducer for a pump wherein the inducer includes a hub, a plurality of radially extending substantially helical blades and a wall member extending about and encompassing an outer periphery of the blades. The improvement comprises forming adjacent pairs of blades and the hub to provide a substantially rectangular cross-sectional flow area which cross-sectional flow area decreases from the inlet end of the inducer to a discharge end of the inducer, resulting in increased inducer efficiency improved suction performance, reduced susceptibility to cavitation, reduced susceptibility to hub separation and reduced fabrication costs.

Dunn, Charlton (Calabasas, CA); Subbaraman, Maria R. (Canoga Park, CA)

1989-01-01

278

Cavitation-resistant inducer  

DOEpatents

An improvement in an inducer for a pump is disclosed wherein the inducer includes a hub, a plurality of radially extending substantially helical blades and a wall member extending about and encompassing an outer periphery of the blades. The improvement comprises forming adjacent pairs of blades and the hub to provide a substantially rectangular cross-sectional flow area which cross-sectional flow area decreases from the inlet end of the inducer to a discharge end of the inducer, resulting in increased inducer efficiency improved suction performance, reduced susceptibility to cavitation, reduced susceptibility to hub separation and reduced fabrication costs. 11 figs.

Dunn, C.; Subbaraman, M.R.

1989-06-13

279

Cavitation phenomena in mechanical heart valves: studied by using a physical impinging rod system.  

PubMed

When studying mechanical heart valve cavitation, a physical model allows direct flow field and pressure measurements that are difficult to perform with actual valves, as well as separate testing of water hammer and squeeze flow effects. Movable rods of 5 and 10 mm diameter impinged same-sized stationary rods to simulate squeeze flow. A 24 mm piston within a tube simulated water hammer. Adding a 5 mm stationary rod within the tube generated both effects simultaneously. Charged-coupled device (CCD) laser displacement sensors, strobe lighting technique, laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and high fidelity piezoelectric pressure transducers measured impact velocities, cavitation images, squeeze flow velocities, vortices, and pressure changes at impact, respectively. The movable rods created cavitation at critical impact velocities of 1.6 and 1.2 m/s; squeeze flow velocities were 2.8 and 4.64 m/s. The isolated water hammer created cavitation at 1.3 m/s piston speed. The combined piston and stationary rod created cavitation at an impact speed of 0.9 m/s and squeeze flow of 3.2 m/s. These results show squeeze flow alone caused cavitation, notably at lower impact velocity as contact area increased. Water hammer alone also caused cavitation with faster displacement. Both effects together were additive. The pressure change at the vortex center was only 150 mmHg, which cannot generate the magnitude of pressure drop required for cavitation bubble formation. Cavitation occurred at 3-5 m/s squeeze flow, significantly different from the 14 m/s derived by Bernoulli's equation; the temporal acceleration of unsteady flow requires further study. PMID:20490686

Lo, Chi-Wen; Chen, Sheng-Fu; Li, Chi-Pei; Lu, Po-Chien

2010-10-01

280

Exploring Bubbles  

NASA Astrophysics Data System (ADS)

Bubbles provide an enjoyable and festive medium through which to teach many concepts within the science topics of light, color, chemistry, force, air pressure, electricity, buoyancy, floating, density, among many others. In order to determine the nature of children's engagement within a museum setting and the learning opportunities of playing with bubbles, I went to a children's interactive museum located in a metropolitan city in the Northeastern part of the United States.

O'Geary, Melissa A.

281

Anticipatory model of cavitation  

NASA Astrophysics Data System (ADS)

The Anticipatory System (AS) formalism developed by Robert Rosen provides some insight into the problem of embedding intelligent behavior in machines. AS emulates the anticipatory behavior of biological systems. AS bases its behavior on its expectations about the near future and those expectations are modified as the system gains experience. The expectation is based on an internal model that is drawn from an appeal to physical reality. To be adaptive, the model must be able to update itself. To be practical, the model must run faster than real-time. The need for a physical model and the requirement that the model execute at extreme speeds, has held back the application of AS to practical problems. Two recent advances make it possible to consider the use of AS for practical intelligent sensors. First, advances in transducer technology make it possible to obtain previously unavailable data from which a model can be derived. For example, acoustic emissions (AE) can be fed into a Bayesian system identifier that enables the separation of a weak characterizing signal, such as the signature of pump cavitation precursors, from a strong masking signal, such as a pump vibration feature. The second advance is the development of extremely fast, but inexpensive, digital signal processing hardware on which it is possible to run an adaptive Bayesian-derived model faster than real-time. This paper reports the investigation of an AS using a model of cavitation based on hydrodynamic principles and Bayesian analysis of data from high-performance AE sensors.

Kercel, Stephen W.; Allgood, Glenn O.; Dress, William B.; Hylton, James O.

1999-03-01

282

Numerical investigations of shock-bubble interactions in mercury  

NASA Astrophysics Data System (ADS)

The bubble collapse induced by the shock-bubble interactions in mercury is investigated numerically to evaluate the cavitation damage. The ghost fluid method (GFM) is applied to the present analysis. Riemann solutions are utilized to correct the values at boundary nodes to suppress the pressure oscillations near the interface. The interactions between an air bubble and a plane shock wave in mercury with the infinite boundary are compared with those in water. It is shown that the collapse time of a bubble in mercury is longer than that in water. The interaction with the incident shock wave leads to the bubble deformation and the formation of liquid jet in the final stage of collapse. Higher impulsive pressure is generated in the mercury when the jet impacts the bubble surface. Also, the interactions between an air bubble and a plane shock wave in mercury in the vicinity of a glass wall are simulated. The mercury and glass are evaluated by using the stiffened gas equations. The motions of three phases for air, mercury, and glass are solved directly coupling the GFM with the level set method. Since the acoustic impedance of glass is smaller than the mercury, the expansion waves are reflected at the glass wall when the shock wave hits the glass wall. Consequently, the bubble takes a similar motion to that near a compliant wall; the glass wall is attracted toward the bubble during the bubble collapse; the collapse time of a bubble becomes shorter than that of an isolated bubble; the jet impacts the bubble surface in the later stage of collapse. Strong shock waves are formed from the bubble when the bubble rebounds as well as when the jet impacts the bubble surface. The shock waves hit the glass wall and lead to the depression of the glass surface.

Takahira, Hiroyuki; Matsuno, Takahiro; Shuto, Keisuke

2008-07-01

283

High-speed jetting and spray formation from bubble collapse.  

PubMed

A method to create impacting jets at the micrometer length scale by means of a collapsing cavitation bubble is presented. A focused shock wave from a lithotripter leads to the nucleation of a cavitation bubble below a hole of 25 ?m diameter etched in a silicon plate. The plate is placed at an air-water interface. The expansion and collapse of the bubble leads to two separate jets--an initial slow jet of velocity ?10 m/s and a later faster jet of velocity ?50 m/s. The jets subsequently impact coaxially, resulting in a circular sheet of liquid in the plane perpendicular to their axis. The sheet is characterized by a ring of droplets at its rim and breaks up into a spray as the shock pressure is increased. The results demonstrate an approach to create a high-speed jet and fine spray on demand at the micrometer scale. PMID:22400617

Karri, Badarinath; Avila, Silvestre Roberto Gonzalez; Loke, Yee Chong; O'Shea, Sean J; Klaseboer, Evert; Khoo, Boo Cheong; Ohl, Claus-Dieter

2012-01-01

284

Identifying the Inertial Cavitation Pressure Threshold and Skull Effects in a Vessel Phantom Using Focused Ultrasound and Microbubbles  

NASA Astrophysics Data System (ADS)

Using Focused Ultrasound (FUS) and microbubbles to open the blood-brain barrier (BBB) has been shown promising for brain drug delivery. However, the exact mechanism behind the opening remains unknown. Here, the effects of the murine skull on the threshold of inertial cavitation were investigated. In order to investigate the pressure threshold for inertial cavitation of preformed microbubbles during sonication, passive cavitation detection in conjunction with B-mode imaging was used. A cylindrical vessel with a 610-?m diameter inside a polyacrylamide gel was generated within a polyacrylamide gel to simulate large blood vessels. Definity® (Lantheus Medical Imaging, MA, USA) microbubbles with a 1.1-3.3 ?m in diameter at 2.5×107 bubbles/mL were injected into the channel before sonication (frequency: 1.525 MHz; pulse length: 100 cycles; PRF: 10 Hz; sonication duration: 2 s) through an excised mouse skull. A cylindrically focused hydrophone, confocal with the FUS transducer, acted as a passive cavitation detector (PCD) to identify the threshold. A 7.5 MHz linear array with the field-of-view perpendicular to the axial length of the FUS beam was also used to image the occurrence of bubble fragmentation. The broadband spectral response acquired at the passive cavitation detector (PCD) and the B-mode images identified the occurrence and location of the inertial cavitation, respectively. Findings indicated that the peak-rarefactional pressure threshold was approximately equal to 0.45 MPa at the presence or the absence of the skull. However, the skull induced 10-50% lower inertial cavitation dose. Mouse skulls did not affect the pressure threshold of inertial cavitation but resulted in a lower inertial cavitation dose. The broadband response could be captured through the murine skull, so the same PCD setup can be used in future in vivo applications.

Tung, Yao-Sheng; Choi, James J.; Konofagou, Elisa E.

2010-03-01

285

SURFACE OSCILLATIONS AND JET DEVELOPMENT IN PULSATING BUBBLES Department of Physios, University of Mississippi, Oxford, MS. 38677. U.S.A.  

E-print Network

cyclic liquid jets in pulsating bubbles that have been acoustically trapped near a platform and theoretical effort has been directed toward the study of liquid jet production in cavitation research /1-8/. These high velocity jets of water appear to be the dominant mechanism in cavitation damage and thus

Boyer, Edmond

286

Drying by cavitation and poroelastic relaxations in porous media with macroscopic pores connected by nanoscale throats.  

PubMed

We investigate the drying dynamics of porous media with two pore diameters separated by several orders of magnitude. Nanometer-sized pores at the edge of our samples prevent air entry, while drying proceeds by heterogeneous nucleation of vapor bubbles-cavitation-in the liquid in micrometer-sized voids within the sample. We show that the dynamics of cavitation and drying are set by the interplay of the deterministic poroelastic mass transport in the porous medium and the stochastic nucleation process. Spatiotemporal patterns emerge in this unusual reaction-diffusion system, with temporal oscillations in the drying rate and variable roughness of the drying front. PMID:25302891

Vincent, Olivier; Sessoms, David A; Huber, Erik J; Guioth, Jules; Stroock, Abraham D

2014-09-26

287

Drying by Cavitation and Poroelastic Relaxations in Porous Media with Macroscopic Pores Connected by Nanoscale Throats  

E-print Network

We investigate the drying dynamics of porous media with two pore diameters separated by several orders of magnitude. Nanometer-sized pores at the edge of our samples prevent air entry, while drying proceeds by heterogeneous nucleation of vapor bubbles (cavitation) in the liquid in micrometer-sized voids within the sample. We show that the dynamics of cavitation and drying are set by the interplay of the deterministic poroelastic mass transport in the porous medium and the stochastic nucleation process. Spatio-temporal patterns emerge in this unusual reaction-diffusion system, with temporal oscillations in the drying rate and variable roughness of the drying front.

Olivier Vincent; David A. Sessoms; Erik J. Huber; Jules Guioth; Abraham D. Stroock

2014-02-27

288

Drying by Cavitation and Poroelastic Relaxations in Porous Media with Macroscopic Pores Connected by Nanoscale Throats  

NASA Astrophysics Data System (ADS)

We investigate the drying dynamics of porous media with two pore diameters separated by several orders of magnitude. Nanometer-sized pores at the edge of our samples prevent air entry, while drying proceeds by heterogeneous nucleation of vapor bubbles—cavitation—in the liquid in micrometer-sized voids within the sample. We show that the dynamics of cavitation and drying are set by the interplay of the deterministic poroelastic mass transport in the porous medium and the stochastic nucleation process. Spatiotemporal patterns emerge in this unusual reaction-diffusion system, with temporal oscillations in the drying rate and variable roughness of the drying front.

Vincent, Olivier; Sessoms, David A.; Huber, Erik J.; Guioth, Jules; Stroock, Abraham D.

2014-09-01

289

Effect of Liquid Viscosity on a Liquid Jet Produced by the Collapse of a Laser-Induced Bubble near a Rigid Boundary  

Microsoft Academic Search

The collapse of a laser-induced cavitation bubble near a rigid boundary and its dependence on liquid (kinematic) viscosity are investigated experimentally by fiber-coupling optical beam deflection (OBD). Cavitation bubble tests are performed using a mixture of glycerin and water of various concentrations, and the viscosity ranges from 1.004× 10-6 to 51.30× 10-6 m2\\/s. Combining the detection principles of this detector

Xiu-mei Liu; Jie He; Jian Lu; Xiao-wu Ni

2009-01-01

290

Current research in cavitating fluid films  

NASA Technical Reports Server (NTRS)

A review of the current research of cavitation in fluid films is presented. Phenomena and experimental observations include gaseous cavitation, vapor cavitation, and gas entrainment. Cavitation in flooded, starved, and dynamically loaded journal bearings, as well as squeeze films are reviewed. Observations of cavitation damage in bearings and the possibility of cavitation between parallel plates with microasperities were discussed. The transcavity fluid transport process, meniscus motion and geometry or form of the film during rupture, and reformation were summarized. Performance effects were related to heat transfer models in the cavitated region and hysteresis influence on rotor dynamics coefficients. A number of cavitation algorithms was presented together with solution procedures using the finite difference and finite element methods. Although Newtonian fluids were assumed in most of the discussions, the effect of non-Newtonian fluids on cavitation was also discussed.

Brewe, D. E. (editor); Ball, J. H. (editor); Khonsari, M. M. (editor)

1990-01-01

291

Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity  

NASA Astrophysics Data System (ADS)

in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1-1.0 MPa, 0.01-0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO2, under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 Mw 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 ± 15 cm and 23 ± 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.

Crews, Jackson B.; Cooper, Clay A.

2014-09-01

292

Cavitation Inception on Microparticles: A Self-Propelled Particle Accelerator  

Microsoft Academic Search

Corrugated, hydrophilic particles with diameters between 30 and 150 mum are found to cause cavitation inception at their surfaces when they are exposed to a short, intensive tensile stress wave. The growing cavity accelerates the particle into translatory motion until the tensile stress decreases, and subsequently the particle separates from the cavity. The cavity growth and particle detachment are modeled

Manish Arora; Claus-Dieter Ohl; Knud Aage Mørch

2004-01-01

293

Taking control of cavitation repair  

SciTech Connect

Eliminating surprises and emergencies is the key of mastering cavitation-erosion repair. Innovations in runner design, new welding techniques and materials, and integrated maintenance scheduling add to that mastery.

Fulton, E. [Hydro Review, Kansas City, MO (United States)

1994-05-01

294

Cavitation in superplastic composites  

SciTech Connect

The cavitation of superplastic 6061/Si{sub 3}N{sub 4p} deformed at several levels of stress and at a temperature of 833 K in a constant stress tensile test.These composites have been examined by measuring cavity volume fraction and by electron microscopic observation. Cavities have always formed at interfaces between matrix and particles. In specimens deformed at higher stress than 10 MPa, many lamellar cavities as well as cracks have appeared at interfaces in addition to granular cavities which have been observed over all stress levels. The lamellar crack-like cavities seem to be associated with rapid decreases of total elongation from 500% at a stress of 10 MPa to 300% at a stress of 11 MPa. It could be presumed that the lamellar cavities have been generated by excessive stress to some critical strength of the interface.

Iwasaki, Hajime [Himeji Institute of Technology, Hyogo (Japan). Dept. of Materials Science and Engineering; Mabuchi, Mamoru [Government Industrial Research Institute, Nagoya (Japan); Higashi, Kenji [Univ. of Osaka Prefecture, Sakai (Japan). Dept. of Mechanical Engineering

1993-12-31

295

Application of two turbulence models for computation of cavitating flows in a centrifugal pump  

NASA Astrophysics Data System (ADS)

To seek a better numerical method to simulate the cavitating flow field in a centrifugal pump, the applications between RNG k- ? and LES turbulence model were compared by using the Zwart-Gerber-Belamri cavitation model. It was found that both the models give almost the same results with respect to pump performance and cavitation evolutions including growth, local contraction, stability and separation in the impeller passage. But the LES model can not only capture the pump suction recirculation and the low frequency fluctuation caused by it, but also combine the changes of the shaft frequency amplitude acting on the impeller with the cavitation unstable characteristics. Thus the LES model has more advantages than RNG k- ? model in calculating the unsteady cavitating flow in a centrifugal pump.

He, M.; Guo, Q.; Zhou, L. J.; Wang, Z. W.; Wang, X.

2013-12-01

296

Photoelectrochemical behaviour of uniform growth TiO2 nanotubes via bubble blowing synthesised in ethylene glycol with hydrogen peroxide.  

PubMed

Uniformly sized TiO2 nanotubes with high aspect ratios were synthesised on a large substrate (100 mm x 100 mm) via the bubbling system through anodisation of Ti in ethylene glycol containing 5 wt% NH4F and 5 wt% H2O2. The benefits of bubbling system in producing uniformly sized TiO2 nanotubes throughout the Ti foil are illustrated. Moreover, the effects of applied voltage and fluoride content on the resulting nanotubes were also considered. Such uniform sized TiO2 nanotubes are a key to produce hydrogen efficiently using PEC cell. The results show higher photocurrent responses for the high aspect ratio, uniform TiO2 nanotubes because of excellent interfacial electron transfer. PMID:22852347

Lai, Chin Wei; Sreekantan, Srimala; Lockman, Zainovia

2012-05-01

297

Analysis of freeze-thaw embolism in conifers. The interaction between cavitation pressure and tracheid size.  

PubMed

Ice formation in the xylem sap produces air bubbles that under negative xylem pressures may expand and cause embolism in the xylem conduits. We used the centrifuge method to evaluate the relationship between freeze-thaw embolism and conduit diameter across a range of xylem pressures (Px) in the conifers Pinus contorta and Juniperus scopulorum. Vulnerability curves showing loss of conductivity (embolism) with Px down to -8 MPa were generated with versus without superimposing a freeze-thaw treatment. In both species, the freeze-thaw plus water-stress treatment caused more embolism than water stress alone. We estimated the critical conduit diameter (Df) above which a tracheid will embolize due to freezing and thawing and found that it decreased from 35 microm at a Px of -0.5 MPa to 6 microm at -8 MPa. Further analysis showed that the proportionality between diameter of the air bubble nucleating the cavitation and the diameter of the conduit (kL) declined with increasingly negative Px. This suggests that the bubbles causing cavitation are smaller in proportion to tracheid diameter in narrow tracheids than in wider ones. A possible reason for this is that the rate of dissolving increases with bubble pressure, which is inversely proportional to bubble diameter (La Place's law). Hence, smaller bubbles shrink faster than bigger ones. Last, we used the empirical relationship between Px and Df to model the freeze-thaw response in conifer species. PMID:16377751

Pittermann, Jarmila; Sperry, John S

2006-01-01

298

Role of H2O2 in the fluctuating patterns of COD (chemical oxygen demand) during the treatment of palm oil mill effluent (POME) using pilot scale triple frequency ultrasound cavitation reactor.  

PubMed

Palm oil mill effluent (POME) is a highly contaminating wastewater due to its high chemical oxygen demand (COD) and biochemical oxygen demand (BOD). Conventional treatment methods require longer residence time (10-15 days) and higher operating cost. Owing to this, finding a suitable and efficient method for the treatment of POME is crucial. In this investigation, ultrasound cavitation technology has been used as an alternative technique to treat POME. Cavitation is the phenomenon of formation, growth and collapse of bubbles in a liquid. The end process of collapse leads to intense conditions of temperature and pressure and shock waves which assist various physical and chemical transformations. Two different ultrasound systems i.e. ultrasonic bath (37 kHz) and a hexagonal triple frequency ultrasonic reactor (28, 40 and 70 kHz) of 15 L have been used. The results showed a fluctuating COD pattern (in between 45,000 and 60,000 mg/L) while using ultrasound bath alone, whereas a non-fluctuating COD pattern with a final COD of 27,000 mg/L was achieved when hydrogen peroxide was introduced. Similarly for the triple frequency ultrasound reactor, coupling all the three frequencies resulted into a final COD of 41,300 mg/L compared to any other individual or combination of two frequencies. With the possibility of larger and continuous ultrasonic cavitational reactors, it is believed that this could be a promising and a fruitful green process engineering technique for the treatment of POME. PMID:24485395

Manickam, Sivakumar; Abidin, Norhaida binti Zainal; Parthasarathy, Shridharan; Alzorqi, Ibrahim; Ng, Ern Huay; Tiong, Timm Joyce; Gomes, Rachel L; Ali, Asgar

2014-07-01

299

Effect of the probe geometry on dynamics of cavitation  

NASA Astrophysics Data System (ADS)

Cavitation bubbles accompany explosive evaporation of water after pulsed energy deposition during endosurgery. Bubbles collapsing at the time of an endo-probe produce a powerful and damaging water jet propagating forward in the axial direction of the probe. We demonstrate that formation of this flow and associated tissue damage can be prevented by application of the concave probes that slow the propagation of the back boundary of the bubble. A similar effect can be achieved by positioning an obstacle to the flow, such as a ring or a pick tip in a close proximity to the back, side or front of the tip. Dependence of the flow dynamics on geometry of the probe was studied using fast flash photography and particle velocimetry. With a flat tip a maximal jet velocity of 80 m/s is achieved at a pulse energy of 0.12 mJ, while with an optimized concave probe the jet is completely stopped. The maximal distance between the probe and the tissue at which cells were affected by the water jet was measured using choriallantoic membrane of a chick embryo and Propidium Iodide staining. Changing the tip geometry from flat or convex to an optimized concave shape resulted in reduction of the damage distance by a factor of 4 with pulse energies varying from 0.02 to 0.75 mJ. Elimination of the water jet dramatically improves precision and safety of the pulsed endosurgery reducing the axial damage zone to a size of the cavitation bubble at its maximal expansion.

Palanker, Daniel V.; Vankov, Alexander; Miller, Jason

2002-06-01

300

A Shock-Wave Generator of a Single Cavitation Bubble  

Microsoft Academic Search

A modified version of a flat electromagnetic converter for enhancing the amplitude of the pressure of a shock wave using the Laptev–Trishin method and reducing the duration of an acoustic pulse is described. The interference of a focused edge diffraction rarefaction wave and a wave reflected from a free surface is used to form a narrow space–time negative-pressure region. The

G. N. Sankin

2003-01-01

301

Leverage bubble  

NASA Astrophysics Data System (ADS)

Leverage is strongly related to liquidity in a market and lack of liquidity is considered a cause and/or consequence of the recent financial crisis. A repurchase agreement is a financial instrument where a security is sold simultaneously with an agreement to buy it back at a later date. Repurchase agreement (repo) market size is a very important element in calculating the overall leverage in a financial market. Therefore, studying the behavior of repo market size can help to understand a process that can contribute to the birth of a financial crisis. We hypothesize that herding behavior among large investors led to massive over-leveraging through the use of repos, resulting in a bubble (built up over the previous years) and subsequent crash in this market in early 2008. We use the Johansen-Ledoit-Sornette (JLS) model of rational expectation bubbles and behavioral finance to study the dynamics of the repo market that led to the crash. The JLS model qualifies a bubble by the presence of characteristic patterns in the price dynamics, called log-periodic power law (LPPL) behavior. We show that there was significant LPPL behavior in the market before that crash and that the predicted range of times predicted by the model for the end of the bubble is consistent with the observations.

Yan, Wanfeng; Woodard, Ryan; Sornette, Didier

2012-01-01

302

Non-Invasive Thrombolysis Using Pulsed Ultrasound Cavitation Therapy - Histotripsy  

PubMed Central

Clinically available thrombolysis techniques are limited by either slow reperfusion (drugs) or invasiveness (catheters), and carry significant risks of bleeding. In this study, the feasibility of using histotripsy as an efficient and non-invasive thrombolysis technique was investigated. Histotripsy fractionates soft tissue through controlled cavitation using focused, short, high-intensity ultrasound pulses. In-vitro blood clots formed from fresh canine blood were treated by histotripsy. The treatment was applied using a focused 1-MHz transducer, with 5-cycle pulses at a pulse repetition rate of 1 kHz. Acoustic pressures varying from 2 – 12 MPa peak negative pressure were tested. Our results show that histotripsy can perform effective thrombolysis with ultrasound energy alone. Histotripsy thrombolysis only occurred at peak negative pressure ?6 MPa when initiation of a cavitating bubble cloud was detected using acoustic backscatter monitoring. Blood clots weighing 330 mg were completely broken down by histotripsy in 1.5 – 5 minutes. The clot was fractionated to debris with >96% weight smaller than 5 ?m diameter. Histotripsy thrombolysis treatment remained effective under a fast, pulsating flow (a circulatory model) as well as in static saline. Additionally, we observed that fluid flow generated by a cavitation cloud can attract, trap, and further break down clot fragments. This phenomenon may provide a non-invasive method to filter and eliminate hazardous emboli during thrombolysis. PMID:19854563

Maxwell, Adam D.; Cain, Charles A.; Duryea, Alexander P.; Yuan, Lingqian; Gurm, Hitinder S.; Xu, Zhen

2009-01-01

303

Observation and quantification of cavitation on a mechanical heart valve with an electro-hydraulic total artificial heart.  

PubMed

In previous studies, we investigated the cavitation phenomenon in a mechanical heart valve using an electro-hydraulic total artificial heart. With this system, a 50% glycerin solution kept at 37 degrees C was used as the working fluid. We reported that most of the cavitation bubbles were observed near the valve stop and were caused by the squeeze flow. However, in these studies, the effect of the partial pressure of CO(2) on the mechanical heart valve cavitation was neglected. In this study, in order to investigate the effect of the partial pressure of CO(2) on mechanical heart valve cavitation using an electro-hydraulic total artificial heart, we controlled the partial pressure of the CO(2) in vitro. A 25-mm Medtronic Hall valve was installed in the mitral position of an electro-hydraulic total artificial heart. In order to quantify the mechanical heart valve cavitation, we used a high-speed camera. Even though cavitation intensity slightly increased with increases in the PCO(2) at heart rates of 60, 70 and 100 bpm, throughout the experiment, there was no significant difference between the PCO(2) and cavitation intensity. PMID:16685674

Lee, H; Taenaka, Y

2006-03-01

304

Submicron-bubble-enhanced focused ultrasound for blood-brain barrier disruption and improved CNS drug delivery.  

PubMed

The use of focused ultrasound (FUS) with microbubbles has been proven to induce transient blood-brain barrier opening (BBB-opening). However, FUS-induced inertial cavitation of microbubbles can also result in erythrocyte extravasations. Here we investigated whether induction of submicron bubbles to oscillate at their resonant frequency would reduce inertial cavitation during BBB-opening and thereby eliminate erythrocyte extravasations in a rat brain model. FUS was delivered with acoustic pressures of 0.1-4.5 MPa using either in-house manufactured submicron bubbles or standard SonoVue microbubbles. Wideband and subharmonic emissions from bubbles were used to quantify inertial and stable cavitation, respectively. Erythrocyte extravasations were evaluated by in vivo post-treatment magnetic resonance susceptibility-weighted imaging, and finally by histological confirmation. We found that excitation of submicron bubbles with resonant frequency-matched FUS (10 MHz) can greatly limit inertial cavitation while enhancing stable cavitation. The BBB-opening was mainly caused by stable cavitation, whereas the erythrocyte extravasation was closely correlated with inertial cavitation. Our technique allows extensive reduction of inertial cavitation to induce safe BBB-opening. Furthermore, the safety issue of BBB-opening was not compromised by prolonging FUS exposure time, and the local drug concentrations in the brain tissues were significantly improved to 60 times (BCNU; 18.6 µg versus 0.3 µg) by using chemotherapeutic agent-loaded submicron bubbles with FUS. This study provides important information towards the goal of successfully translating FUS brain drug delivery into clinical use. PMID:24788566

Fan, Ching-Hsiang; Liu, Hao-Li; Ting, Chien-Yu; Lee, Ya-Hsuan; Huang, Chih-Ying; Ma, Yan-Jung; Wei, Kuo-Chen; Yen, Tzu-Chen; Yeh, Chih-Kuang

2014-01-01

305

Submicron-Bubble-Enhanced Focused Ultrasound for Blood-Brain Barrier Disruption and Improved CNS Drug Delivery  

PubMed Central

The use of focused ultrasound (FUS) with microbubbles has been proven to induce transient blood–brain barrier opening (BBB-opening). However, FUS-induced inertial cavitation of microbubbles can also result in erythrocyte extravasations. Here we investigated whether induction of submicron bubbles to oscillate at their resonant frequency would reduce inertial cavitation during BBB-opening and thereby eliminate erythrocyte extravasations in a rat brain model. FUS was delivered with acoustic pressures of 0.1–4.5 MPa using either in-house manufactured submicron bubbles or standard SonoVue microbubbles. Wideband and subharmonic emissions from bubbles were used to quantify inertial and stable cavitation, respectively. Erythrocyte extravasations were evaluated by in vivo post-treatment magnetic resonance susceptibility-weighted imaging, and finally by histological confirmation. We found that excitation of submicron bubbles with resonant frequency-matched FUS (10 MHz) can greatly limit inertial cavitation while enhancing stable cavitation. The BBB-opening was mainly caused by stable cavitation, whereas the erythrocyte extravasation was closely correlated with inertial cavitation. Our technique allows extensive reduction of inertial cavitation to induce safe BBB-opening. Furthermore, the safety issue of BBB-opening was not compromised by prolonging FUS exposure time, and the local drug concentrations in the brain tissues were significantly improved to 60 times (BCNU; 18.6 µg versus 0.3 µg) by using chemotherapeutic agent-loaded submicron bubbles with FUS. This study provides important information towards the goal of successfully translating FUS brain drug delivery into clinical use. PMID:24788566

Ting, Chien-Yu; Lee, Ya-Hsuan; Huang, Chih-Ying; Ma, Yan-Jung; Wei, Kuo-Chen; Yen, Tzu-Chen; Yeh, Chih-Kuang

2014-01-01

306

Spatial control of cavitation in therapeutic ultrasound  

E-print Network

Inertial cavitation has been implicated as the primary mechanism for a host of emerging applications. In all these applications, the main concern is to induce cavitation in perfectly controlled locations in the field; this ...

Gauthier, Thomas P., 1980-

2005-01-01

307

Dynamics of Vapour Bubbles in Nucleate Boiling. 2; Evolution of Thermally Controlled Bubbles  

NASA Technical Reports Server (NTRS)

The previously developed dynamic theory of growth and detachment of vapour bubbles under conditions of nucleate pool boiling is applied to study motion and deformation of a bubble evolving at a single nucleation site. The bubble growth is presumed to be thermally controlled, and two components of heat transfer to the bubble are accounted of: the one from the bulk of surrounding liquid and the one due to heat conduction across a liquid microlayer formed underneath the bubble. Bubble evolution is governed by the buoyancy and an effective surface tension force, both the forces making the bubble centre of mass move away from the wall and, thus, assisting its detachment. Buoyancy-controlled and surface-tension-controlled regimes are considered separately in a meticulous way. The duration of the whole process of bubble evolution till detachment, the rate of growth, and the bubble departure size are found as functions of time and physical and operating parameters. Some repeatedly observed phenomena, such as an influence of gravity on the growth rate, are explained. Inferences of the model agree qualitatively with available experimental evidence, and conclusions pertaining to the dependence on gravity of the bubble radius at detachment and the whole time of the bubble development when being attached to the wall are confirmed quantitatively.

Buyevich, Yu A.; Webbon, Bruce W.; Callaway, Robert (Technical Monitor)

1995-01-01

308

Interaction of two differently sized oscillating bubbles in a free field.  

PubMed

Most real life bubble dynamics applications involve multiple bubbles, for example, in cavitation erosion prevention, ultrasonic baths, underwater warfare, and medical applications involving microbubble contrast agents. Most scientific dealings with bubble-bubble interaction focus on two similarly sized bubbles. In this study, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography. Four types of bubble behavior were observed, namely, jetting toward each other, jetting away from each other, bubble coalescence, and a behavior termed the "catapult" effect. In-phase bubbles jet toward each other, while out-of-phase bubbles jet away from each other. There exists a critical phase difference that separates the two regimes. The behavior of the bubbles is fully characterized by their dimensionless separation distance, their phase difference, and their size ratio. It is also found that for bubbles with large size difference, the smaller bubble behaves similarly to a single bubble oscillating near a free surface. PMID:22304190

Chew, Lup Wai; Klaseboer, Evert; Ohl, Siew-Wan; Khoo, Boo Cheong

2011-12-01

309

Optical and acoustic monitoring of bubble cloud dynamics at a tissue-fluid interface in ultrasound tissue erosion  

PubMed Central

Short, high-intensity ultrasound pulses have the ability to achieve localized, clearly demarcated erosion in soft tissue at a tissue-fluid interface. The primary mechanism for ultrasound tissue erosion is believed to be acoustic cavitation. To monitor the cavitating bubble cloud generated at a tissue-fluid interface, an optical attenuation method was used to record the intensity loss of transmitted light through bubbles. Optical attenuation was only detected when a bubble cloud was seen using high speed imaging. The light attenuation signals correlated well with a temporally changing acoustic backscatter which is an excellent indicator for tissue erosion. This correlation provides additional evidence that the cavitating bubble cloud is essential for ultrasound tissue erosion. The bubble cloud collapse cycle and bubble dissolution time were studied using the optical attenuation signals. The collapse cycle of the bubble cloud generated by a high intensity ultrasound pulse of 4–14 ?s was ~40–300 ?s depending on the acoustic parameters. The dissolution time of the residual bubbles was tens of ms long. This study of bubble dynamics may provide further insight into previous ultrasound tissue erosion results. PMID:17471753

Xu, Zhen; Hall, Timothy L.; Fowlkes, J. Brian; Cain, Charles A.

2009-01-01

310

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 101, NO. B8, PAGES 17,457-17,465, AUGUST 10, 1996 Waves of bubbles in basaltic magmas and lavas  

E-print Network

of bubbles in basaltic magmas and lavas MichaelManga· Department of Geologyand Geophysics becomeunstableand form risingwavesor layersof bubbles. We derivea setofmodelequationsforthetwo-phase(bubble. The spacingof layersis determinedby a balancebetweenthe growth of bubbles and hydrodynamic self

Manga, Michael

311

Cavitation noise studies on marine propellers  

Microsoft Academic Search

Experimental observations are described of cavitation inception and noise from five model propellers, three basic and two modified, tested in the open jet section of the Indian Institute of Science high-speed water tunnel facility. Extensive experiments on the three basic propellers of different design, which included visualization of cavitation and measurements of noise, showed that the dominant type of cavitation

S. D. Sharma; K. Mani; V. H. Arakeri

1990-01-01

312

Surge instability on a cavitating propeller  

Microsoft Academic Search

This study details experiments investigating a previously unrecognized surge instability on a cavitating pro- peller in a water tunnel. The surge instability is first explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Similarities between the instability and previously docu- mented cavitation phenomena are noted. Measurements of the radiated pressure are then obtained,

Mark E. Duttweiler; Christopher E. Brennen

2002-01-01

313

A revised cavitation model for cryogenic cavitating flow computations  

NASA Astrophysics Data System (ADS)

The inducer operates in cryogenic liquids which have a lower liquid to vapor density ratio, significantly higher slopes of pressure-temperature saturation curve and other quantities such as latent heat and thermal conductivity, resulting in substantial thermal effects and strong variations in fluid properties. The goal of our overall efforts is to establish a predictive tool for cryogenic cavitating flows, especially the transport-based cavitation model. Specifically, a Rayleigh-Plesset Based transport model is presented which considered the thermal effect. A Revised cavitation model is introduced and the computational results of the Revised cavitation model is compared against the previous Kubota cavitation model under cryogenic conditions. Compared with the results of Kubota model, the reduced magnitude of the cavity length is larger for the Revised model and it can simulate the observed "frosty" appearance within the cavity better. The maximum temperature and pressure depressions for the cases show lower and the pressure returns to the free-stream pressure faster for the Revised model. The Revised model can capture the temperature and pressure depressions more exactly in the cavity region, especially at the rear end of the cavity, since the intensity of the evaporation and condensation show large distinction for the previous and the Revised models. The evaporation intensity is lowered, while the magnitude of the condensation term is stronger for the Revised model due to the thermal effect term. As evaporation occurs, the revised term of the evaporation rate is negative which will suppress the evaporation intensity. With increasing the cavitation intensity, the revised term of the evaporation rate become higher. For the condensation term, the revised term of the condensation rate is positive as condensation occurs which will enhance the condensation intensity. It also can be found that the revised term of the condensation rate is higher when the condensation intensity is larger. The Revised model is more sensitive to the thermal effect of cavitation. The effectiveness of the Revised model is confirmed by using experimental data in cryogenic cavitation.

Shi, S. G.; Wu, Q.; Wang, G. Y.

2012-11-01

314

Numerical investigation of the effect of properties of the liquid on cavitation at solid surfaces  

SciTech Connect

Numerical calculations were carried out on a computer with Mercon`s method to investigate the effect of properties of the liquid, namely, density, pressure of the saturated vapor (gas content in a bubble), surface tension, viscosity, and wave resistance, on the instantaneous radius, velocity, and shape of the surface of a compressed cavitation bubble for various distances between two parallel solid walls confining the liquid, times, and angular coordinates. The theoretical relations found agree with earlier experimental data. Recommendations are given for using the present results in practical development of technological sonication processes and in operation of ultrasonic equipment and hydrosystems.

Kuvshinov, G.I.; Ernetti, G.; Francescutto, A. [Institute of Applied Physics, Minsk (Belarus)] [and others

1994-10-01

315

Fluctuation dynamics and 1/ f spectra characterizing the acoustic cavitation of liquids  

NASA Astrophysics Data System (ADS)

The dynamics of acoustic cavitation in water and glycerin is studied experimentally. The power spectra and distribution functions of fluctuations are determined. In transient regimes, bubble structures in the form of fractal clusters are formed near the ultrasonic radiator. The power spectra have the form 1/ f, and the distribution functions of local fluctuations differ from the Gaussian ones and exhibit the scale invariance property.

Skokov, V. N.; Reshetnikov, A. V.; Vinogradov, A. V.; Koverda, V. P.

2007-04-01

316

Simultaneous size and velocity measurements of cavitating microbubbles using interferometric laser imaging  

Microsoft Academic Search

In this paper, interferometric laser imaging droplet sizing—ILIDS—is applied to incipient cavitation in the wake of a marine\\u000a propeller model with the aim to evaluate simultaneously bubbles velocity and diameter. Until now, the feasibility of this\\u000a technique has been demonstrated especially in sprays of water droplets in air where an optimal light scattering is obtained\\u000a thanks to the spherical shape

G. Lacagnina; S. Grizzi; M. Falchi; F. Di Felice; G. P. Romano

2011-01-01

317

Simulation of the effects of cavitation and anatomy in the shock path of model lithotripters  

PubMed Central

We report on recent efforts to develop predictive models for the pressure and other flow variables in the focal region of shock wave lithotripters. Baseline simulations of three representative lithotripters (electrohydraulic, electromagnetic, and piezoelectric) compare favorably with in vitro experiments (in a water bath). We proceed to model and investigate how shock focusing is altered by the presence of material interfaces associated with different types of tissue encountered along the shock path, and by the presence of cavitation bubbles that are excited by tensile pressures associated with the focused shock wave. We use human anatomical data, but simplify the description by assuming that the tissue behaves as a fluid, and by assuming cylindrical symmetry along the shock path. Scattering by material interfaces is significant, and regions of high pressure amplitudes (both compressive and tensile) are generated almost 4 cm postfocus. Bubble dynamics generate secondary shocks whose strength depends on the density of bubbles and the pulse repetition frequency (PRF). At sufficiently large densities, the bubbles also attenuate the shock. Together with experimental evidence, the simulations suggest that high PRF may be counter-productive for stone comminution. Finally, we discuss how the lithotripter simulations can be used as input to more detailed physical models that attempt to characterize the mechanisms by which collapsing cavitation models erode stones, and by which shock waves and bubbles may damage tissue. PMID:21063697

Krimmel, Jeff; Colonius, Tim; Tanguay, Michel

2011-01-01

318

Cavitation dynamics of medtronic hall mechanical heart valve prosthesis: fluid squeezing effect.  

PubMed

The cause of cavitation in mechanical heart valves is investigated with Medtronic Hall tilting disk valves in an in vitro flow system simulating the closing event in the mitral position. Recordings of pressure wave forms and photographs in the vicinity of the inflow surface of the valve are attempted under controlled transvalvular loading rates averaged during valve closing period. The results revealed presence of a local flow field with a very high velocity around the seat stop of mechanical heart valves that could induce pressure reduction below liquid vapor pressure and a cloud of cavitation bubbles. The analysis of the results indicates that the "fluid squeezing" between the stop and occluder as the main cause of cavitation in Medtronic Hall valves. The threshold loading rate for cavitation initiation around the stop was found to be very low (300 and 400 mmHg/s; half the predicted normal human loading rate that was estimated to be 750 mmHg/s) because even a mild impact created a high speed local flow field on the occluder surface that could induce pressure reduction below vapor pressure. The present study suggests that mechanical heart valves with stops at the edge of major orifice region are more vulnerable to cavitation, and hence, have higher potential for damage on valve components and formed elements in blood. PMID:8833080

Lee, C S; Chandran, K B; Chen, L D

1996-02-01

319

Temporal effect of inertial cavitation with and without microbubbles on surface deformation of agarose S gel in the presence of 1-MHz focused ultrasound.  

PubMed

Sonoporation has the potential to deliver extraneous molecules into a target tissue non-invasively. There have been numerous investigations of cell membrane permeabilization induced by microbubbles, but very few studies have been carried out to investigate sonoporation by inertial cavitation, especially from a temporal perspective. In the present paper, we show the temporal variations in nano/micro-pit formations following the collapse of inertial cavitation bubbles, with and without Sonazoid® microbubbles. Using agarose S gel as a target material, erosion experiments were conducted in the presence of 1-MHz focused ultrasound applied for various exposure times, Tex (0.002-60 s). Conventional microscopy was used to measure temporal variations in micrometer-scale pit numbers, and atomic force microscopy utilized to detect surface roughness on a nanometer scale. The results demonstrated that nanometer-scale erosion was predominantly caused by Sonazoid® microbubbles and C4F10 gas bubbles for 0.002 scavitation bubbles such as C4F10 gas bubbles and vapor bubbles, increased exponentially with increasing Tex in the range 0.1 scavitation-induced sonoporation can produce various pore sizes in membranes, enabling the delivery of external molecules of differing sizes into cells or tissues. PMID:25130135

Tomita, Y; Matsuura, T; Kodama, T

2015-01-01

320

Seismically Initiated Carbon Dioxide Gas Bubble Growth in Groundwater: A Mechanism for Co-seismic Borehole Water Level Rise and Remotely Triggered Secondary Seismicity  

NASA Astrophysics Data System (ADS)

Visualization experiments, core-scale laboratory experiments, and numerical simulations were conducted to examine the transient effect of dilational seismic wave propagation on pore fluid pressure in aquifers hosting groundwater that is near saturation with respect to dissolved carbon dioxide (CO2) gas. Groundwater can become charged with dissolved CO2 through contact with gas-phase CO2 in the Earth's crust derived from magma degasing, metamorphism, and biogenic processes. The propagation of dilational seismic waves (e.g., Rayleigh and p-waves) causes oscillation of the mean normal confining stress and pore fluid pressure. When the amplitude of the pore fluid pressure oscillation is large enough to drive the pore fluid pressure below the bubble pressure, an aqueous-to-gas-phase transition can occur in the pore space, which causes a buildup of pore fluid pressure and reduces the inter-granular effective stress under confined conditions. In visualization experiments conducted in a Hele-Shaw cell representing a smooth-walled, vertically oriented fracture, millisecond-scale pressure perturbations triggered bubble nucleation and growth lasting tens of seconds, with resulting pore fluid overpressure proportional to the magnitude of the pressure perturbation. In a Berea sandstone core flooded with initially under-saturated aqueous CO2 under conditions representative of a confined aquifer, rapid reductions in confining stress triggered transient pore pressure rise up to 0.7 MPa (100 psi) overpressure on a timescale of ~10 hours. The rate of pore pressure buildup in the first 100 seconds was proportional to the saturation with respect to dissolved CO 2 at the pore pressure minimum. Sinusoidal confining stress oscillations on a Berea sandstone core produced excess pore fluid pressure after the oscillations were terminated. Confining stress oscillations in the 0.1-0.4 MPa (15-60 psi) amplitude range and 0.05-0.30 Hz frequency band increased the pore fluid pressure by 13-60 cm of freshwater. Co-seismic borehole water level increases of the same magnitude were observed in Parkfield, California, and Long Valley caldera, California, in response to the propagation of a Rayleigh wave in the same amplitude and frequency range produced by the June 28, 1992 MW 7.3 Landers, California, earthquake. Co-seismic borehole water level rise is well documented in the literature, but the mechanism is not well understood, and the results of core-scale experiments indicate that seismically initiated CO2 gas bubble nucleation and growth in groundwater is a reasonable mechanism. Remotely triggered secondary seismicity is also well documented, and the reduction of effective stress due to CO2 bubble nucleation and growth in critically loaded faults may potentially explain how, for example, the June 28, 1992 MW 7.3 Landers, California, earthquake triggered seismicity as far away as Yellowstone, Wyoming, 1250 km from the hypocenter. A numerical simulation was conducted using Euler's method and a first-order kinetic model to compute the pore fluid pressure response to confining stress excursions on a Berea sandstone core flooded with initially under-saturated aqueous CO2. The model was calibrated on the pore pressure response to a rapid drop and later recovery of the confining stress. The model predicted decreasing overpressure as the confining stress oscillation frequency increased from 0.05 Hz to 0.30 Hz, in contradiction with the experimental results and field observations, which exhibit larger excess pore fluid pressure in response to higher frequency oscillations. The limitations of the numerical model point to the important influence of non-ideal behavior arising from a discontinuous gas phase and complex dynamics at the gas-liquid interface.

Crews, Jackson B.

321

A study of liquid jets formed by bubble collapse under shock waves in elastic and Newtonian liquids 1 Dedicated to the memory of Professor Gianni Astarita 1  

Microsoft Academic Search

This paper describes a study of the formation of liquid jets in elastic and Newtonian liquids. The technique used to study this phenomenon involves a shock wave, emanating from the collapse of a cavitation bubble, which causes a gas bubble underneath the free surface of a liquid column to collapse, thereby producing a liquid jet. A comparison of the jets

P. R Williams; P. M Williams; S. W. J Brown

1998-01-01

322

Mechanistic analysis of cavitation assisted transesterification on biodiesel characteristics.  

PubMed

The influence of sonoluminescence transesterification on biodiesel physicochemical properties was investigated and the results were compared to those of traditional mechanical stirring. This study was conducted to identify the mechanistic features of ultrasonication by coupling statistical analysis of the experiments into the simulation of cavitation bubble. Different combinations of operational variables were employed for alkali-catalysis transesterification of palm oil. The experimental results showed that transesterification with ultrasound irradiation could change the biodiesel density by about 0.3kg/m(3); the viscosity by 0.12mm(2)/s; the pour point by about 1-2°C and the flash point by 5°C compared to the traditional method. Furthermore, 93.84% of yield with alcohol to oil molar ratio of 6:1 could be achieved through ultrasound assisted transesterification within only 20min. However, only 89.09% of reaction yield was obtained by traditional macro mixing/heating under the same condition. Based on the simulated oscillation velocity value, the cavitation phenomenon significantly contributed to generation of fine micro emulsion and was able to overcome mass transfer restriction. It was found that the sonoluminescence bubbles reached the temperature of 758-713K, pressure of 235.5-159.55bar, oscillation velocity of 3.5-6.5cm/s, and equilibrium radius of 17.9-13.7 times greater than its initial size under the ambient temperature of 50-64°C at the moment of collapse. This showed that the sonoluminescence bubbles were in the condition in which the decomposition phenomena were activated and the reaction rate was accelerated together with a change in the biodiesel properties. PMID:24981808

Sajjadi, Baharak; Abdul Aziz, A R; Ibrahim, Shaliza

2015-01-01

323

Suppressing bubble shielding effect in shock wave lithotripsy by low intensity pulsed ultrasound.  

PubMed

Extracorporeal shock wave lithotripsy (ESWL) has been used as an effective modality to fragment kidney calculi. Because of the bubble shielding effect in the pre-focal region, the acoustic energy delivered to the focus is reduced. Low pulse repetition frequency (PRF) will be applied to dissolve these bubbles for better stone comminution efficiency. In this study, low intensity pulsed ultrasound (LIPUS) beam was aligned perpendicular to the axis of a shock wave (SW) lithotripter at its focus. The light transmission was used to evaluate the compressive wave and cavitation induced by SWs without or with a combination of LIPUS for continuous sonication. It is found that bubble shielding effect becomes dominated with the SW exposure and has a greater significant effect on cavitation than compressive wave. Using the combined wave scheme, the improvement began at the 5th pulse and gradually increased. Suppression effect on bubble shielding is independent on the trigger delay, but increases with the acoustic intensity and pulse duration of LIPUS. The peak negative and integral area of light transmission signal, which present the compressive wave and cavitation respectively, using our strategy at PRF of 1 Hz are comparable to those using SW alone at PRF of 0.1 Hz. In addition, high-speed photography confirmed the bubble activities in both free field and close to a stone surface. Bubble motion in response to the acoustic radiation force by LIPUS was found to be the major mechanism of suppressing bubble shielding effect. There is a 2.6-fold increase in stone fragmentation efficiency after 1000 SWs at PRF of 1 Hz in combination with LIPUS. In summary, combination of SWs and LIPUS is an effective way of suppressing bubble shielding effect and, subsequently, improving cavitation at the focus for a better outcome. PMID:25173067

Wang, Jen-Chieh; Zhou, Yufeng

2015-01-01

324

Cavitation contributes substantially to tensile creep in silicon nitride  

SciTech Connect

During tensile creep of a hot isostatically pressed (HIPed) silicon nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and temperature range produces very little cavitation. A stress exponent that increases with stress ({dot {var_epsilon}} {proportional_to} {sigma}{sup n}, 2 < n < 7) characterizes the tensile creep response, while the compressive creep response exhibits a stress dependence of unity. Furthermore, under the same stress and temperature, the material creeps nearly 100 times faster in tension than in compression. Transmission electron microscopy (TEM) indicates that the cavities formed during tensile creep occur in pockets of residual crystalline silicate phase located at silicon nitride multigrain junctions. Small-angle X-ray scattering (SAXS) from crept material quantifies the size distribution of cavities observed in TEM and demonstrates that cavity addition, rather than cavity growth, dominates the cavitation process. These observations are in accord with a model for creep based on the deformation of granular materials in which the microstructure must dilate for individual grains t slide past one another. During tensile creep the silicon nitride grains remain rigid; cavitation in the multigrain junctions allows the silicate to flow from cavities to surrounding silicate pockets, allowing the dilation of the microstructure and deformation of the material. Silicon nitride grain boundary sliding accommodates this expansion and leads to extension of the specimen. In compression, where cavitation is suppressed, deformation occurs by solution-reprecipitation of silicon nitride.

Luecke, W.E.; Wiederhorn, S.M.; Hockey, B.J.; Krause, R.F. Jr.; Long, G.G. [National Institute of Standards and Technology, Gaithersburg, MD (United States)

1995-08-01

325

Stochastic-field cavitation model  

NASA Astrophysics Data System (ADS)

Nonlinear phenomena can often be well described using probability density functions (pdf) and pdf transport models. Traditionally, the simulation of pdf transport requires Monte-Carlo codes based on Lagrangian "particles" or prescribed pdf assumptions including binning techniques. Recently, in the field of combustion, a novel formulation called the stochastic-field method solving pdf transport based on Eulerian fields has been proposed which eliminates the necessity to mix Eulerian and Lagrangian techniques or prescribed pdf assumptions. In the present work, for the first time the stochastic-field method is applied to multi-phase flow and, in particular, to cavitating flow. To validate the proposed stochastic-field cavitation model, two applications are considered. First, sheet cavitation is simulated in a Venturi-type nozzle. The second application is an innovative fluidic diode which exhibits coolant flashing. Agreement with experimental results is obtained for both applications with a fixed set of model constants. The stochastic-field cavitation model captures the wide range of pdf shapes present at different locations.

Dumond, J.; Magagnato, F.; Class, A.

2013-07-01

326

Spatial and temporal observation of phase-shift nano-emulsions assisted cavitation and ablation during focused ultrasound exposure.  

PubMed

Background: Phase-shift nano-emulsions (PSNEs) with a small initial diameter in nanoscale have the potential to leak out of the blood vessels and to accumulate at the target point of tissue. At desired location, PSNEs can undergo acoustic droplet vaporization (ADV) process, change into gas bubbles and enhance focused ultrasound efficiency. The threshold of droplet vaporization and influence of acoustic parameters have always been research hotspots in order to spatially control the potential of bioeffects and optimize experimental conditions. However, when the pressure is much higher than PSNEs' vaporization threshold, there were little reports on their cavitation and thermal effects. Object: In this study, PSNEs induced cavitation and ablation effects during pulsed high-intensity focused ultrasound (HIFU) exposure were investigated, including the spatial and temporal information and the influence of acoustic parameters. Methods: Two kinds of tissue-mimicking phantoms with uniform PSNEs were prepared because of their optical transparency. The Sonoluminescence (SL) method was employed to visualize the cavitation activities. And the ablation process was observed as the heat deposition could produce white lesion. Results: Precisely controlled HIFU cavitation and ablation can be realized at a relatively low input power. But when the input power was high, PSNEs can accelerate cavitation and ablation in pre-focal region. The cavitation happened layer by layer advancing the transducer. While the lesion appeared to be separated into two parts, one in pre-focal region stemmed from one point and grew quickly, the other in focal region grew much more slowly. The influence of duty cycle has also been examined. Longer pulse off time would cause heat transfer to the surrounding media, and generate smaller lesion. On the other hand, this would give outer layer bubbles enough time to dissolve, and inner bubbles can undergo violent collapse and emit bright light. PMID:24746925

Qiao, Yangzi; Zong, Yujin; Yin, Hui; Chang, Nan; Li, Zhaopeng; Wan, Mingxi

2014-09-01

327

Measuring the surface tension of soap bubbles  

NASA Technical Reports Server (NTRS)

The objectives are for students to gain an understanding of surface tension, to see that pressure inside a small bubble is larger than that inside a large bubble. These concepts can be used to explain the behavior of liquid foams as well as precipitate coarsening and grain growth. Equipment, supplies, and procedures are explained.

Sorensen, Carl D.

1992-01-01

328

Instability and Subsequent Evolution of Electroweak Bubbles  

E-print Network

Bubbles in a first-order electroweak phase transition are nucleated with radii $R_0$ and expand with velocity $v$. If $v$ is subsonic, a bubble becomes unstable to non-spherical perturbations when its radius is roughly $10^4\\, R_0$. These perturbations accelerate the transition, and the effective velocity of bubble growth rapidly becomes supersonic. The transition should subsequently proceed spherically via detonation. If for some reason the onset of detonation is postponed, the surface area of the bubbles may be enhanced by $10^5$. We discuss consequences for electroweak baryogenesis.

Marc Kamionkowski; Katherine Freese

1992-08-04

329

A Fractional Fourier Transform Analysis of a Bubble Excited by an Ultrasonic Chirp  

E-print Network

. If the pressure amplitude of the signal is relatively low the oscillations will be stable and lin- ear, a mathematical model which describes the dynamics of a bubble subjected to an external acoustic pressure. Oscillations of this type are denoted as stable cavitation. As the pressure increases the oscillations become

Mottram, Nigel

330

BUBBLE DYNAMICS AT GAS-EVOLVING ELECTRODES  

SciTech Connect

Nucleation of bubbles, their growth by diffusion of dissolved gas to the bubble surface and by coalescence, and their detachment from the electrode are all very fast phenomena; furthermore, electrolytically generated bubbles range in size from ten to a few hundred microns; therefore, magnification and high speed cinematography are required to observe bubbles and the phenomena of their growth on the electrode surface. Viewing the action from the front side (the surface on which the bubbles form) is complicated because the most important events occur close to the surface and are obscured by other bubbles passing between the camera and the electrode; therefore, oxygen was evolved on a transparent tin oxide "window" electrode and the events were viewed from the backside. The movies showed that coalescence of bubbles is very important for determining the size of bubbles and in the chain of transport processes; growth by diffusion and by coalescence proceeds in series and parallel; coalescing bubbles cause significant fluid motion close to the electrode; bubbles can leave and reattach; and bubbles evolve in a cycle of growth by diffusion and different modes of coalescence. An analytical solution for the primary potential and current distribution around a spherical bubble in contact with a plane electrode is presented. Zero at the contact point, the current density reaches only one percent of its undisturbed value at 30 percent of the radius from that point and goes through a shallow maximum two radii away. The solution obtained for spherical bubbles is shown to apply for the small bubbles of electrolytic processes. The incremental resistance in ohms caused by sparse arrays of bubbles is given by {Delta}R = 1.352 af/kS where f is the void fraction of gas in the bubble layer, a is the bubble layer thickness, k is the conductivity of gas free electrolyte, and S is the electrode area. A densely populated gas bubble layer on an electrode was modeled as a hexagonal array of dielectric spheres. Accurately machined lucite spheres were placed one at a time in one end of a hexagonal cell which simulated the unit cell of such an array. The resistance as a function of gas bubble layer packing density sharply increased as close packing was approached. Because the interaction of the fields around bubbles closely spaced in the direction perpendicular to the current dominates the added resistance, and because there is a tri-modal distribution of bubble sizes in a bubble layer, the Distribution Model of Meredith and Tobias (16), derived for three dimensional gas dispersions, approximately predicted the conductivity of a bubble layer at void fractions greater than 0.3. At moderate-to-high current densities, the bubble layer in a cell having an interelectrode gap of half a centimeter could increase the ohmic resistance by as much as 20 percent.

Sides, Paul J.

1980-12-01

331

Shadowgraph, Schlieren and interferometry in a 2D cavitating channel flow  

NASA Astrophysics Data System (ADS)

Cavitation plays an important role in fuel atomization mechanisms, but the physics of cavitation and its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required to support the development and the validation of numerical models and the design of tomorrow's injectors, in the context of pollutant and fuel consumption reduction. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test oil (ISO 4113). Three different optical techniques are proposed to investigate the channel flow, with the pressure drop between upstream and downstream chambers as a parameter. A shadowgraph-like imaging technique allows the observation of cavitation inception and vapor cavities development throughout the channel. The technique also reveals the presence of density gradients (pressure or temperature) in the channel flow. However, this additional information is balanced by difficulties in image interpretation, which are discussed in the paper. In addition, a combination of Schlieren technique and interferometric imaging is used to measure the density fields inside the channel. The three techniques results are carefully analyzed and confronted. These results reveal a wealth of information on the flow, with pressure waves generated by bubble collapses, turbulence in the wake of vapor cavities and bubble survival in flow regions of high pressure. Our results also show that cavitation inception is located in the shear layers between the recirculation zones and the main flow, relatively far from the inlet corner, where the pressure is minimum in average. To explain this behavior, we propose a scenario of cavitation inception based on the occurrence and the growing of instabilities in the shear layers.

Mauger, Cyril; Méès, Loïc; Michard, Marc; Azouzi, Alexandre; Valette, Stéphane

2012-12-01

332

Cavitation Fatigue. Embolism and Refilling Cycles Can Weaken the Cavitation Resistance of Xylem1  

E-print Network

Cavitation Fatigue. Embolism and Refilling Cycles Can Weaken the Cavitation Resistance of Xylem1 their ability to with- stand negative pressures? Or does the act of cavita- tion fatigue the vessels in some way

Stiller, Volker

333

Study on the bubble transport mechanism in an acoustic standing wave field.  

PubMed

The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller-Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton's second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of pressure amplitude or a decrease of bubble size forces bubbles larger than their resonant size to arrive at the target plate at lower heights, while the trajectories of smaller bubbles are less influenced by these factors. The test cell is also suitable for testing the effects of drag force on the bubble motion and for studying the bubble behavior near a surface. PMID:21719064

Xi, Xiaoyu; Cegla, Frederic B; Lowe, Michael; Thiemann, Andrea; Nowak, Till; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander

2011-12-01

334

Cavitation noise studies on marine propellers  

NASA Astrophysics Data System (ADS)

Experimental observations are described of cavitation inception and noise from five model propellers, three basic and two modified, tested in the open jet section of the Indian Institute of Science high-speed water tunnel facility. Extensive experiments on the three basic propellers of different design, which included visualization of cavitation and measurements of noise, showed that the dominant type of cavitation was in the form of tip vortex cavitation, accompanied by leading edge suction side sheet cavitation in its close vicinity, and the resultant noise depended on parameters such as the advance coefficient, the cavitation number, and the propeller geometry. Of these, advance coefficient was found to have the maximum influence not only on cavitation noise but also on the inception of cavitation. Noise levels and frequencies of spectra obtained from all the three basic propellers at conditions near inception and different advance coefficient values, when plotted in the normalized form as suggested by Blake, resulted in a universal spectrum which would be useful for predicting cavitation noise at prototype scales when a limited extent of cavitation is expected in the same form as observed on the present models. In an attempt to delay the onset of tip vortex cavitation, the blades of two of the three basic propellers were modified by drilling small holes in the tip and leading edge areas. Studies on the modified propellers showed that the effectiveness of the blade modification was apparently stronger at low advance coefficient values and depended on the blade sectional profile. Measurements of cavitation noise indicated that the modification also improved the acoustic performance of the propellers as it resulted in a complete attenuation of the low-frequency spectral peaks, which were prominent with the basic propellers. In addition to the above studies, which were conducted under uniform flow conditions, one of the basic propellers was tested in the simulated wake of a typical single screw ship. The wake was simulated by using a wire screen technique. Observations of cavitation and measurement of noise clearly showed that the presence of the wake had a strong influence on the propeller cavitation and noise performance. Cavitation was found to be of the cloud type, which generated very intense noise compared to that generated by tip vortex cavitation along with leading edge suction side sheet cavitation in the uniform flow conditions. The noise spectra obtained with wake simulation also are presented in a normalized form to be of general utility.

Sharma, S. D.; Mani, K.; Arakeri, V. H.

1990-04-01

335

Express Letter Radial variations of melt viscosity around growing bubbles  

E-print Network

strain rates of the £ow [5,6], the bubble-bearing magma fragments and erupts explosively [7,8]. The gas variations of melt viscosity on the growth of bub- bles. We analyze the hydrodynamic equations of the melt-viscosity rind that forms at the bubble^melt interface. 2. The hydrodynamics of the melt around a growing bubble

Lyakhovsky, Vladimir

336

Dynamics of cavitation clouds within a high-intensity focused ultrasonic beam  

NASA Astrophysics Data System (ADS)

In this experimental study, we generate a 500 kHz high-intensity focused ultrasonic beam, with pressure amplitude in the focal zone of up to 1.9 MPa, in initially quiescent water. The resulting pressure field and behavior of the cavitation bubbles are measured using high-speed digital in-line holography. Variations in the water density and refractive index are used for determining the spatial distribution of the acoustic pressure nonintrusively. Several cavitation phenomena occur within the acoustic partially standing wave caused by the reflection of sound from the walls of the test chamber. At all sound levels, bubbly layers form in the periphery of the focal zone in the pressure nodes of the partial standing wave. At high sound levels, clouds of vapor microbubbles are generated and migrate in the direction of the acoustic beam. Both the cloud size and velocity vary periodically, with the diameter peaking at the pressure nodes and velocity at the antinodes. A simple model involving linearized bubble dynamics, Bjerknes forces, sound attenuation by the cloud, added mass, and drag is used to predict the periodic velocity of the bubble cloud, as well as qualitatively explain the causes for the variations in the cloud size. The analysis shows that the primary Bjerknes force and drag dominate the cloud motion, and suggests that the secondary Bjerknes force causes the oscillations in the cloud size.

Lu, Yuan; Katz, Joseph; Prosperetti, Andrea

2013-07-01

337

Analysis of Freeze-Thaw Embolism in Conifers. The Interaction between Cavitation Pressure and Tracheid Size1  

PubMed Central

Ice formation in the xylem sap produces air bubbles that under negative xylem pressures may expand and cause embolism in the xylem conduits. We used the centrifuge method to evaluate the relationship between freeze-thaw embolism and conduit diameter across a range of xylem pressures (Px) in the conifers Pinus contorta and Juniperus scopulorum. Vulnerability curves showing loss of conductivity (embolism) with Px down to ?8 MPa were generated with versus without superimposing a freeze-thaw treatment. In both species, the freeze-thaw plus water-stress treatment caused more embolism than water stress alone. We estimated the critical conduit diameter (Df) above which a tracheid will embolize due to freezing and thawing and found that it decreased from 35 ?m at a Px of ?0.5 MPa to 6 ?m at ?8 MPa. Further analysis showed that the proportionality between diameter of the air bubble nucleating the cavitation and the diameter of the conduit (kL) declined with increasingly negative Px. This suggests that the bubbles causing cavitation are smaller in proportion to tracheid diameter in narrow tracheids than in wider ones. A possible reason for this is that the rate of dissolving increases with bubble pressure, which is inversely proportional to bubble diameter (La Place's law). Hence, smaller bubbles shrink faster than bigger ones. Last, we used the empirical relationship between Px and Df to model the freeze-thaw response in conifer species. PMID:16377751

Pittermann, Jarmila; Sperry, John S.

2006-01-01

338

Cavitation in elastomeric solids: II--Onset-of-cavitation surfaces for Neo-Hookean materials  

E-print Network

Cavitation in elastomeric solids: II--Onset-of-cavitation surfaces for Neo-Hookean materials Oscar, the theory is used to determine onset-of-cavitation surfaces for Neo-Hookean solids where the defects cavity in a Neo-Hookean block under multi-axial loading. Good agreement is found for a wide range

Nakamura, Toshio

339

Hydrodynamic Cavitation for Food and Water Processing  

Microsoft Academic Search

Hydrodynamic cavitation, which was and is still looked upon as an unavoidable nuisance in the flow systems, can be a serious\\u000a contender as an alternative to acoustic cavitation for intensification of different physical and chemical processing applications.\\u000a Hydrodynamic cavitation results in the generation of hot spots, highly reactive free radicals and turbulence associated with\\u000a liquid circulation currents, which can result

Parag R. Gogate

2011-01-01

340

Radial oscillation of a gas bubble in a fluid as a problem in canonical perturbation theory  

NASA Astrophysics Data System (ADS)

The oscillation of a gas bubble is in a fluid is of interest in many areas of physics and technology. Lord Rayleigh treated the pressure developed in the collapse of cavitation bubbles and developed an expression for the collapse period. Minnaert developed a harmonic oscillator approximation to bubble oscillation in his study of the sound produced by running water. Besides recent interest in bubble oscillation in connection to sonoluminescence, an understanding of oscillating bubbles is of important to oceanographers studying the sound spectrum produced by water waves, geophysicists employing air guns as acoustic probes, mechanical engineers concerned with erosion of turbine blades, and military engineers concerned with the acoustic signatures developed by the propeller screws of ships and submarines. For the oceanographer, Minnaert's approximation is useful, for the latter two examples, Lord Rayleigh's analysis is appropriate. For the case of the airgun, a period of twice Rayleigh's period for the ``total collapse'' of the cavitation bubble is often cited as a good approximation for the period of an air bubble ejected from an air gun port, typically at ˜2000 psi), however for the geophysical example, numerical integration is employed from the outset to determine the dynamics of the bubble and the emitted acoustic energy. On the one hand, a bubble can be treated as a harmonic oscillator in the small amplitude regime, whereas even in the relatively moderate pressure regime characteristic of air guns the oscillation is strongly nonlinear and amplitude dependent. Is it possible to develop an analytic approximation that affords insight into the behavior of a bubble beyond the harmonic approximation of Minnaert? In this spirit, the free radial oscillation of a gas bubble in a fluid is treated as a problem in canonical perturbation theory. Several orders of the expansion are determined in order to explore the dependence of the oscillation frequency with bubble amplitude. The expansion to second order is inverted to express the time dependence of the oscillation.

Stephens, James

2006-11-01

341

Grain Boundary Cavitation in Molybdenum  

Microsoft Academic Search

THE formation of cavities at grain boundaries under creep conditions had been observed in many metals and may lead to intercrystalline failure1. We have observed such cavitation in molybdenum wires of 0.010 mm diam. heated by electron bombardment to temperatures between 1,500° and 2,500° C (that is, above 60 per cent of the absolute melting point) and strained a few

P. J. Bowles; G. A. Geach

1963-01-01

342

Acoustic bubble removal method  

NASA Technical Reports Server (NTRS)

A method is described for removing bubbles from a liquid bath such as a bath of molten glass to be used for optical elements. Larger bubbles are first removed by applying acoustic energy resonant to a bath dimension to drive the larger bubbles toward a pressure well where the bubbles can coalesce and then be more easily removed. Thereafter, submillimeter bubbles are removed by applying acoustic energy of frequencies resonant to the small bubbles to oscillate them and thereby stir liquid immediately about the bubbles to facilitate their breakup and absorption into the liquid.

Trinh, E. H.; Elleman, D. D.; Wang, T. G. (inventors)

1983-01-01

343

Effect of Liquid Viscosity on a Liquid Jet Produced by the Collapse of a Laser-Induced Bubble near a Rigid Boundary  

NASA Astrophysics Data System (ADS)

The collapse of a laser-induced cavitation bubble near a rigid boundary and its dependence on liquid (kinematic) viscosity are investigated experimentally by fiber-coupling optical beam deflection (OBD). Cavitation bubble tests are performed using a mixture of glycerin and water of various concentrations, and the viscosity ranges from 1.004×10-6 to 51.30×10-6 m2/s. Combining the detection principles of this detector with a widely used laser ablation model, actual liquid-jet impact forces are presented for the mentioned viscosity range. In addition, based on the model of a collapsing bubble, some characteristic parameters, such as bubble lifetime, the maximum bubble radius, and liquid-jet impact pressure, are also obtained as a function of liquid viscosity. The main conclusion is that the liquid jet is a dominant factor in cavitation damage and can be modified by liquid viscosity. A high viscosity reduces the liquid-jet impact force and cavitation erosion markedly. The mechanism of the liquid viscosity effect on cavitation erosion has also been discussed.

Liu, Xiu-mei; He, Jie; Lu, Jian; Ni, Xiao-wu

2009-01-01

344

Probing the Bioeffects of Cavitation at the Single-Cell Level  

NASA Astrophysics Data System (ADS)

The primary goal of this dissertation research is to develop an experimental system and associated techniques that can be used to investigate the bioeffects produced by cavitation bubbles at the single cell level. Such information has been lacking due to the randomness and complexity in cavitation inception and subsequent bubble-bubble interaction generated by an acoustic field typically used in therapeutic ultrasound applications. Connection between cavitation activities and bioeffects produced in cells nearby presents another challenge that has not been resolved satisfactorily. In this work, we developed a laser-based system for generating tandem bubbles with a maximum diameter about 50 microm (i.e., on the scale of a single cell) in a microfluidic channel of 25 microm in height and 800 microm in width. We further developed techniques for micropatterning of individual gold dots (15 nm thick and 6 microm in diameter) used for bubble generation, which are precisely aligned at various stand-off distances (SD) from individual islands (32 x 32 microm2) coated with fibronectin used for cell adhesion. The dynamics of tandem bubble interaction with resultant jet formation, microstreaming and vortex flow in the microfluidic channel were captured by high-speed imaging and particle image velocimetry (PIV). The deformation of the target cell was recorded by high-speed imaging as well (using a second camera) immediately after the tandem bubble interaction and assessment of membrane strain was aided with 2 microm sized polystyrene beads attached to the cell membrane. Membrane poration was characterized by uptake of fluorescent propodium iodide (PI) into the target cell, from which the normalized maximum pore size was estimated. Using this experimental system, we have observed the complete process of bubble-bubble interaction with resultant jetting flow, cell deformation, and localized pinpoint membrane rupture with progressive diffusion of macromolecules into the target cell. Furthermore, we observed a clear SD dependence in the treatment outcome produced by the tandem bubbles. At short SD of 10 microm, all treated cells underwent necrosis with high yet unsaturated level of PI uptake, indicating that the cell could not reseal the poration site. At intermediate SD of 20 ˜ 30 microm, 58% to 80% of the cells were observed to have repairable membrane poration with low to medium but saturated level of PI uptake. At long SD of 40 microm, no detectable PI uptake was observed, corresponding to no membrane compromise. Within the repairable membrane poration group, the sub-population of cells that eventually survived without apoptosis increased from about 9% at SD of 20 microm with strong adhesion to about 70% at SD of 30 microm with no adhesion at the leading edge facing the jetting flow. The maximum PI uptake, pore size, and membrane strain estimated could vary by more than an order of magnitude, which is similar to the magnitude of variations in pore size (0.2 ˜ 2 microm) produced by tandem bubbles observed by SEM. The large principal strain (> 500%) with associated high strain-rate (> 106·s -1) produced by the tandem bubbles provide a unique tool to examine the bioeffects of cavitation at the single cell level and potentially a diverse range of applications to be explored.

Yuan, Fang

345

The generation of negative pressure waves for cavitation studies.  

PubMed

A technique for producing strong focused negative pressure waves in water is described. The method is based on the phase inversion of the planar shock wave from an electromagnetic transducer. This is achieved by reflection and focusing at a pressure release boundary. The acoustic concentrator has a phase inverting central element and a phase maintaining annular mirror. Focal pressures of approximately -16 MPa from an initial +5 MPa EMAT source have been measured and the focal volume was found to be approximately the same as that obtained with a conventional ultrasonic lens. The electromagnetic transducer and the parabolic concentrator is an excellent source of cavitation bubbles in water. The focused negative wave has been observed using high speed laser-lit Schlieren photography. PMID:9651598

Carnell, M T; Gentry, T P; Emmony, D C

1998-02-01

346

Bubbles and Superbubbles  

E-print Network

An isolated massive star can blow a bubble, while a group of massive stars can blow superbubbles. In this paper, we examine three intriguing questions regarding bubbles and superbubbles: (1) why don't we see interstellar bubbles around every O star? (2) how hot are the bubble interiors? and (3) what is going on at the hot/cold gas interface in a bubble?

Y. -H. Chu; M. A. Guerrero; R. A. Gruendl

2003-10-10

347

THE ROLE OF INERTIAL CAVITATION IN ACOUSTIC DROPLET VAPORIZATION  

PubMed Central

The vaporization of a superheated droplet emulsion into gas bubbles using ultrasound – termed acoustic droplet vaporization (ADV) – has potential therapeutic applications in embolotherapy and drug delivery. The optimization of ADV for therapeutic applications can be enhanced by understanding the physical mechanisms underlying ADV, which are currently not clearly elucidated. Acoustic cavitation is one possible mechanism. This paper investigates the relationship between the ADV and inertial cavitation (IC) thresholds (measured as peak rarefactional pressures) by studying parameters that are known to influence the IC threshold. These parameters include bulk fluid properties such as gas saturation, temperature, viscosity, and surface tension; droplet parameters such as degree of superheat, surfactant type, and size; and acoustic properties such as pulse repetition frequency and pulse width. In all cases the ADV threshold occurred at a lower rarefactional pressure than the IC threshold indicating that the phase-transition occurs before IC events. The viscosity and temperature of the bulk fluid are shown to influence both thresholds directly and inversely, respectively. An inverse trend is observed between threshold and diameter for droplets in the 1 to 2.5 ? range. Based on a choice of experimental parameters, it is possible to achieve ADV with or without IC. PMID:19473917

Fabiilli, Mario L.; Haworth, Kevin J.; Fakhri, Nasir H.; Kripfgans, Oliver D.; Carson, Paul L.; Fowlkes, J. Brian

2011-01-01

348

Effects of pulse width on nascent laser-induced bubbles for underwater laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

The reason for the significant advantage offered by long-pulse (150 ns) irradiation in underwater laser-induced breakdown spectroscopy (LIBS) is investigated from the point of view of the behavior of nascent cavitation bubbles. Shadowgraphs of nascent bubbles generated by pulsed laser irradiation of Cu targets in water were observed for two different pulse widths, 20 ns and 150 ns. It is clearly seen that the nascent bubble is formed at the leading edge of the laser pulse profile, regardless of the pulse width. Bubbles generated by a 20-ns pulse are characterized by a flat-shape filled with dense matter with intense optical emission, which is in contrast to more hemispherical low-density bubbles observed under the irradiation by a 150-ns pulse. The behavior of the nascent bubbles is consistent with the behavior of the later plasma in the bubbles, which is crucial for observation of well-defined atomic spectral lines for underwater LIBS.

Sakka, Tetsuo; Tamura, Ayaka; Matsumoto, Ayumu; Fukami, Kazuhiro; Nishi, Naoya; Thornton, Blair

2014-07-01

349

In vivo detection of ultrasonically induced cavitation by a fibre-optic technique.  

PubMed

The measurement of cavitation events in tissue in vivo would greatly assist us to better understand how pulsed high energy ultrasound (PHEUS) interacts with living tissues, especially with regard to cancer therapy. To accomplish this, we designed and built a fibre-optic hydrophone. The principle was to couple the light of a laser diode into a lightfibre and to register the ultrasound induced modification of the refractive index in tissue. In this manner, the cavitation event could be quantitatively investigated both in water and in vivo. The structure of the bubble dynamic is in reasonable agreement with theoretical predictions, and in vitro measurements. With the fibre-optic set-up, the pressure signal can also be detected. PHEUS was generated by an electromagnetic source adapted from a commercial lithotripter (Lithostar Siemens). As biological tissue we used the experimental R3327-AT1 Dunning prostate tumor growing subcutaneously in the thigh of male Copenhagen rats. The lifetime of the cavitation bubble in water increased with the energy level of the ultrasonic pulse from 250 microseconds at 13 kV capacitor voltage to 750 microseconds at 21 kV, while the lifetime inside the tumor tissue in vivo increased only from 100 microseconds at 13 kV to 220 microseconds at 21 kV capacitor voltage. PMID:7863570

Huber, P; Debus, J; Peschke, P; Hahn, E W; Lorenz, W J

1994-01-01

350

Cavitation fatigue. Embolism and refilling cycles can weaken the cavitation resistance of xylem.  

PubMed

Although cavitation and refilling cycles could be common in plants, it is unknown whether these cycles weaken the cavitation resistance of xylem. Stem or petiole segments were tested for cavitation resistance before and after a controlled cavitation-refilling cycle. Cavitation was induced by centrifugation, air drying of shoots, or soil drought. Except for droughted plants, material was not significantly water stressed prior to collection. Cavitation resistance was determined from "vulnerability curves" showing the percentage loss of conductivity versus xylem pressure. Two responses were observed. "Resilient" xylem (Acer negundo and Alnus incana stems) showed no change in cavitation resistance after a cavitation-refilling cycle. In contrast, "weakened" xylem (Populus angustifolia, P. tremuloides, Helianthus annuus stems, and Aesculus hippocastanum petioles) showed considerable reduction in cavitation resistance. Weakening was observed whether cavitation was induced by centrifugation, air dehydration, or soil drought. Observations from H. annuus showed that weakening was proportional to the embolism induced by stress. Air injection experiments indicated that the weakened response was a result of an increase in the leakiness of the vascular system to air seeding. The increased air permeability in weakened xylem could result from rupture or loosening of the cellulosic mesh of interconduit pit membranes during the water stress and cavitation treatment. PMID:11161035

Hacke, U G; Stiller, V; Sperry, J S; Pittermann, J; McCulloh, K A

2001-02-01

351

Cavitation Fatigue. Embolism and Refilling Cycles Can Weaken the Cavitation Resistance of Xylem1  

PubMed Central

Although cavitation and refilling cycles could be common in plants, it is unknown whether these cycles weaken the cavitation resistance of xylem. Stem or petiole segments were tested for cavitation resistance before and after a controlled cavitation-refilling cycle. Cavitation was induced by centrifugation, air drying of shoots, or soil drought. Except for droughted plants, material was not significantly water stressed prior to collection. Cavitation resistance was determined from “vulnerability curves” showing the percentage loss of conductivity versus xylem pressure. Two responses were observed. “Resilient” xylem (Acer negundo and Alnus incana stems) showed no change in cavitation resistance after a cavitation-refilling cycle. In contrast, “weakened” xylem (Populus angustifolia, P. tremuloides, Helianthus annuus stems, and Aesculus hippocastanum petioles) showed considerable reduction in cavitation resistance. Weakening was observed whether cavitation was induced by centrifugation, air dehydration, or soil drought. Observations from H. annuus showed that weakening was proportional to the embolism induced by stress. Air injection experiments indicated that the weakened response was a result of an increase in the leakiness of the vascular system to air seeding. The increased air permeability in weakened xylem could result from rupture or loosening of the cellulosic mesh of interconduit pit membranes during the water stress and cavitation treatment. PMID:11161035

Hacke, Uwe G.; Stiller, Volker; Sperry, John S.; Pittermann, Jarmila; McCulloh, Katherine A.

2001-01-01

352

Observation of cavitation during shock wave lithotripsy  

NASA Astrophysics Data System (ADS)

A system was built to detect cavitation in pig kidney during shock wave lithotripsy (SWL) with a Dornier HM3 lithotripter. Active detection, using echo on B-mode ultrasound, and passive cavitation detection (PCD), using coincident signals on confocal, orthogonal receivers, were equally sensitive and were used to interrogate the renal collecting system (urine) and the kidney parenchyma (tissue). Cavitation was detected in urine immediately upon SW administration in urine or urine plus X-ray contrast agent, but in tissue, cavitation required hundreds of SWs to initiate. Localization of cavitation was confirmed by fluoroscopy, sonography, and by thermally marking the kidney using the PCD receivers as high intensity focused ultrasound sources. Cavitation collapse times in tissue and native urine were about the same but less than in urine after injection of X-ray contrast agent. Cavitation, especially in the urine space, was observed to evolve from a sparse field to a dense field with strong acoustic collapse emissions to a very dense field that no longer produced detectable collapse. The finding that cavitation occurs in kidney tissue is a critical step toward determining the mechanisms of tissue injury in SWL. [Work sup ported by NIH (DK43881, DK55674, FIRCA), ONRIFO, CRDF and NSBRI SMS00203.

Bailey, Michael R.; Crum, Lawrence A.; Pishchalnikov, Yuri A.; McAteer, James A.; Pishchalnikova, Irina V.; Evan, Andrew P.; Sapozhnikov, Oleg A.; Cleveland, Robin O.

2005-04-01

353

Second viscosity in transient cavitating pipe flows  

Microsoft Academic Search

The paper presents the results of a research on the use of distributed cavitation quasi-2D models to reproduce experimental runs of cavitating water hammer flow. Two effects due to presence of free gas are taken into account: the first is the dependence of the wavespeed on the pressure; the second is the presence of additional dissipations due to thermodynamic interactions

Giuseppe Pezzinga

2003-01-01

354

Gas bubble dynamics in soft materials  

E-print Network

Epstein and Plesset's seminal work on the rate of gas bubble dissolution and growth in a simple liquid is generalized to render it applicable to a gas bubble embedded in a soft elastic medium. Both the underlying diffusion equation and the expression for the gas bubble pressure were modified to allow for the non-zero shear modulus of the elastic medium. The extension of the diffusion equation results in a trivial shift (by an additive constant) in the value of the diffusion coefficient, and does not change the form of the rate equations. But the use of a Generalized Young-Laplace equation for the bubble pressure resulted in significant differences on the dynamics of bubble dissolution and growth, relative to a simple liquid medium. Depending on whether the salient parameters (solute concentration, initial bubble radius, surface tension, and shear modulus) lead to bubble growth or dissolution, the effect of allowing for a non-zero shear modulus in the Generalized Young-Laplace equation is to speed up the rate ...

Solano-Altamirano, J M; Goldman, Saul

2014-01-01

355

Investigation of the effects of He bubbles on the nucleation, growth and thermal stability of Al–Cu nanoprecipitates in ion implanted Al foils  

Microsoft Academic Search

The effects of He bubbles on the thermal evolution of ?? Al2Cu precipitates in Al matrix are investigated. The Al–Cu precipitates and the He bubbles were produced at the same depth region (?200 nm below the sample surface) by Cu+ and He+ ion implantation followed by furnace annealing in vacuum at temperatures of 200, 250 and 280 °C for 2–5

G Feldmann; P. F. P Fichtner; F. C Zawislak

2004-01-01

356

Bifurcation of ensemble oscillations and acoustic emissions from early stage cavitation clouds in focused ultrasound  

NASA Astrophysics Data System (ADS)

The acoustic emissions from single cavitation clouds at an early stage of development in 0.521 MHz focused ultrasound of varying intensity, are detected and directly correlated to high-speed microscopic observations, recorded at 1 × 106 frames per second. At lower intensities, a stable regime of cloud response is identified whereby bubble-ensembles exhibit oscillations at half the driving frequency, which is also detected in the acoustic emission spectra. Higher intensities generate clouds that develop more rapidly, with increased nonlinearity evidenced by a bifurcation in the frequency of ensemble response, and in the acoustic emissions. A single bubble oscillation model is subject to equivalent ultrasound conditions and fitted to features in the hydrophone and high-speed spectral data, allowing an effective quiescent radius to be inferred for the clouds that evolve at each intensity. The approach indicates that the acoustic emissions originate from the ensemble dynamics and that the cloud acts as a single bubble of equivalent radius in terms of the scattered field. Jetting from component cavities on the periphery of clouds is regularly observed at higher intensities. The results may be of relevance for monitoring and controlling cavitation in therapeutic applications of focused ultrasound, where the phenomenon has the potential to mediate drug delivery from vasculature.

Gerold, Bjoern; Rachmilevitch, Itay; Prentice, Paul

2013-03-01

357

The effect of static pressure on the strength of inertial cavitation events.  

PubMed

Recent investigations of cavitation in fluids pressurized up to 30 MPa found that the intensity of light emissions increased by 1000-fold over that measured for single bubble sonoluminescence. A series of measurements is reported here to extend this original work by resolving the static pressure dependence of the shock wave and light emissions from the first and the most energetic collapses, along with the total shock wave energy and light emissions for the event. Each of these parameters was found to increase with the static pressure of the fluid. Furthermore, the energy of these shock wave and light emissions was found to increase in proportion to the stored acoustic energy in the system. These findings were corroborated using the Gilmore equation to numerically compute the work done by the liquid during the bubble collapse. The overall findings suggest that the increased collapse strength at high static pressure is due to the increased tension required to generate inertial cavitation, and not an increased pressure gradient between the interior of the vaporous bubble and the surrounding liquid. PMID:23039425

Bader, Kenneth B; Mobley, Joel; Church, Charles C; Gaitan, D Felipe

2012-10-01

358

Soap Bubbles and Logic.  

ERIC Educational Resources Information Center

Introduces questions and activities involving soap bubbles which provide students with experiences in prediction and logic. Examines commonly held false conceptions related to the shapes that bubbles take and provides correct explanations for the phenomenon. (ML)

Levine, Shellie-helane; And Others

1986-01-01

359

The role of bubble waiting time in steady nucleate boiling  

SciTech Connect

Experimental results previously reported by Ibrahim and Judd were examined in order to determine the role of bubble waiting time in steady nucleate boiling. The analysis identified that the time elapsed between the formation of bubbles at a nucleation site is the time required for the liquid which replaced the previous bubble to acquire sufficient energy to sustain the growth of the subsequent bubble, and not the time required to establish the conditions required to enable the nucleus, which formed at the nucleation site, to commence growing into a bubble.

Judd, R.L.

1999-11-01

360

Bubble formation at a gas-evolving microelectrode.  

PubMed

The electrolytic production of gas bubbles involves three steps-nucleation, growth, and detachment. Here the growth of hydrogen bubbles and their detachment from a platinum microelectrode of diameter 125 ?m are studied using high-speed photography and overpotential frequency spectrum (noise) analysis. The periodic release of large <800 ?m bubbles-gas oscillator behavior-was often observed, with a corresponding periodic oscillation of the overpotential which is reflected as a main peak and a series of harmonics in the power spectral density. The release frequency is inversely correlated with the bubble size and hydrogen production rate. When the coalescence of bubbles at the electrode surface is inhibited, either chemically with a surfactant or ethylene glycol or hydrodynamically by magnetically induced convection, swarms of small ?50 ?m bubbles are released in an aperiodic stream. The abrupt transition from periodic to aperiodic release occurs when the surface tension falls below 70 mN m(-1). Hydrogen bubble growth is also studied on a transparent platinum thin-film electrode, where the bubble coalescence can be observed directly. It leaves sessile droplets of electrolyte within the footprint of the growing bubble, showing that the growth involves scavenging smaller bubbles from solution due to hydrogen generated directly at the electrode. A possible role of nanobubbles in the lift-off process is discussed. PMID:24694174

Fernández, Damaris; Maurer, Paco; Martine, Milena; Coey, J M D; Möbius, Matthias E

2014-11-01

361

From rational bubbles to crashes  

NASA Astrophysics Data System (ADS)

We study and generalize in various ways the model of rational expectation (RE) bubbles introduced by Blanchard and Watson in the economic literature. Bubbles are argued to be the equivalent of Goldstone modes of the fundamental rational pricing equation, associated with the symmetry-breaking introduced by non-vanishing dividends. Generalizing bubbles in terms of multiplicative stochastic maps, we summarize the result of Lux and Sornette that the no-arbitrage condition imposes that the tail of the return distribution is hyperbolic with an exponent ?<1. We then outline the main results of Malevergne and Sornette, who extend the RE bubble model to arbitrary dimensions d: a number d of market time series are made linearly interdependent via d× d stochastic coupling coefficients. We derive the no-arbitrage condition in this context and, with the renewal theory for products of random matrices applied to stochastic recurrence equations, we extend the theorem of Lux and Sornette to demonstrate that the tails of the unconditional distributions associated with such d-dimensional bubble processes follow power laws, with the same asymptotic tail exponent ?<1 for all assets. The distribution of price differences and of returns is dominated by the same power-law over an extended range of large returns. Although power-law tails are a pervasive feature of empirical data, the numerical value ?<1 is in disagreement with the usual empirical estimates ??3. We then discuss two extensions (the crash hazard rate model and the non-stationary growth rate model) of the RE bubble model that provide two ways of reconciliation with the stylized facts of financial data.

Sornette, D.; Malevergne, Y.

2001-10-01

362

An Anticipatory Model of Cavitation  

SciTech Connect

The Anticipatory System (AS) formalism developed by Robert Rosen provides some insight into the problem of embedding intelligent behavior in machines. AS emulates the anticipatory behavior of biological systems. AS bases its behavior on its expectations about the near future and those expectations are modified as the system gains experience. The expectation is based on an internal model that is drawn from an appeal to physical reality. To be adaptive, the model must be able to update itself. To be practical, the model must run faster than real-time. The need for a physical model and the requirement that the model execute at extreme speeds, has held back the application of AS to practical problems. Two recent advances make it possible to consider the use of AS for practical intelligent sensors. First, advances in transducer technology make it possible to obtain previously unavailable data from which a model can be derived. For example, acoustic emissions (AE) can be fed into a Bayesian system identifier that enables the separation of a weak characterizing signal, such as the signature of pump cavitation precursors, from a strong masking signal, such as a pump vibration feature. The second advance is the development of extremely fast, but inexpensive, digital signal processing hardware on which it is possible to run an adaptive Bayesian-derived model faster than real-time. This paper reports the investigation of an AS using a model of cavitation based on hydrodynamic principles and Bayesian analysis of data from high-performance AE sensors.

Allgood, G.O.; Dress, W.B., Jr.; Hylton, J.O.; Kercel, S.W.

1999-04-05

363

Simulations of Cavitating Cryogenic Inducers  

NASA Technical Reports Server (NTRS)

Simulations of cavitating turbopump inducers at their design flow rate are presented. Results over a broad range of Nss, numbers extending from single-phase flow conditions through the critical head break down point are discussed. The flow characteristics and performance of a subscale geometry designed for water testing are compared with the fullscale configuration that employs LOX. In particular, thermal depression effects arising from cavitation in cryogenic fluids are identified and their impact on the suction performance of the inducer quantified. The simulations have been performed using the CRUNCH CFD[R] code that has a generalized multi-element unstructured framework suitable for turbomachinery applications. An advanced multi-phase formulation for cryogenic fluids that models temperature depression and real fluid property variations is employed. The formulation has been extensively validated for both liquid nitrogen and liquid hydrogen by simulating the experiments of Hord on hydrofoils; excellent estimates of the leading edge temperature and pressure depression were obtained while the comparisons in the cavity closure region were reasonable.

Dorney, Dan (Technical Monitor); Hosangadi, Ashvin; Ahuja, Vineet; Ungewitter, Ronald J.

2004-01-01

364

Histotripsy beyond the "Intrinsic" Cavitation Threshold using Very Short Ultrasound Pulses: "Microtripsy"  

PubMed Central

Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. Conventional histotripsy treatments have used longer pulses from 3 to 10 cycles wherein the lesion-producing bubble cloud generation depends on the pressure-release scattering of very high peak positive shock fronts from previously initiated, sparsely distributed bubbles (the “shock-scattering” mechanism). In our recent work, the peak negative pressure (P?) for generation of dense bubble clouds directly by a single negative half cycle, the “intrinsic threshold,” was measured. In this paper, the dense bubble clouds and resulting lesions (in RBC phantoms and canine tissues) generated by these supra-intrinsic threshold pulses were studied. A 32-element, PZT-8, 500 kHz therapy transducer was used to generate very short (< 2 cycles) histotripsy pulses at a pulse repetition frequency (PRF) of 1 Hz and P? from 24.5 to 80.7 MPa. The results showed that the spatial extent of the histotripsy-induced lesions increased as the applied P? increased, and the sizes of these lesions corresponded well to the estimates of the focal regions above the intrinsic cavitation threshold, at least in the lower pressure regime (P? = 26–35 MPa). The average sizes for the smallest reproducible lesions were approximately 0.9 × 1.7 mm (lateral × axial), significantly smaller than the ?6dB beamwidth of the transducer (1.8 × 4.0 mm). These results suggest that, using the intrinsic threshold mechanism, well-confined and microscopic lesions can be precisely generated and their spatial extent can be estimated based on the fraction of the focal region exceeding the intrinsic cavitation threshold. Since the supra-threshold portion of the negative half cycle can be precisely controlled, lesions considerably less than a wavelength are easily produced, hence the term “microtripsy.” PMID:24474132

Lin, Kuang-Wei; Kim, Yohan; Maxwell, Adam D.; Wang, Tzu-Yin; Hall, Timothy L.; Xu, Zhen; Fowlkes, J. Brian; Cain, Charles A.

2014-01-01

365

Brut: Automatic bubble classifier  

NASA Astrophysics Data System (ADS)

Brut, written in Python, identifies bubbles in infrared images of the Galactic midplane; it uses a database of known bubbles from the Milky Way Project and Spitzer images to build an automatic bubble classifier. The classifier is based on the Random Forest algorithm, and uses the WiseRF implementation of this algorithm.

Beaumont, Christopher; Goodman, Alyssa; Williams, Jonathan; Kendrew, Sarah; Simpson, Robert

2014-07-01

366

Oscillations of soap bubbles  

Microsoft Academic Search

Oscillations of droplets or bubbles of a confined fluid in a fluid environment are found in various situations in everyday life, in technological processing and in natural phenomena on different length scales. Air bubbles in liquids or liquid droplets in air are well-known examples. Soap bubbles represent a particularly simple, beautiful and attractive system to study the dynamics of a

U. Kornek; F. Müller; K. Harth; A. Hahn; S. Ganesan; L. Tobiska; R. Stannarius

2010-01-01

367

Soap Bubbles in Reverse  

Microsoft Academic Search

WHEN sulphuric acid sodium sulphate solution containing surface-active material is dropped into water, bubbles approximately 5 mm. in diameter sinking through water may be observed. Such bubbles are spherical shells of air, with a sphere of acid sodium sulphate within and water outside. They are, in fact, soap bubbles in reverse. Instead of a two-surfaced film of soapy solution in

Leslie Rose

1946-01-01

368

Soap Films and Bubbles.  

ERIC Educational Resources Information Center

Develops and explains a format for a workshop which focuses on soap films and bubbles. The plan consists of: a discussion to uncover what children know about bubbles; explanations of the demonstration equipment; the presentation itself; the assembly of the workshop kit; and time to play with the bubbles. (ML)

Rice, Karen

1986-01-01

369

Stable Coulomb bubbles ?  

E-print Network

Coulomb bubbles, though stable against monopole displacement, are unstable at least with respect to quadrupole and octupole distortions. We show that there exists a temperature at which the pressure of the vapor filling the bubble stabilizes all the radial modes. In extremely thin bubbles, the crispation modes become unstable due to the surface-surface interaction.

L. G. Moretto; K. Tso; G. J. Wozniak

1996-12-12

370

Cavitation pressure in liquid helium  

Microsoft Academic Search

Recent experiments have suggested that, at low enough temperature, the homogeneous nucleation of bubbles occurs in liquid helium near the calculated spinodal limit. This was done in pure superfluid helium 4 and in pure normal liquid helium 3. However, in such experiments, where the negative pressure is produced by focusing an acoustic wave in the bulk liquid, the local amplitude

Frederic Caupin; Sebastien Balibar

2001-01-01

371

The Isolated Bubble Regime in Pool Nucleate Boiling  

NASA Technical Reports Server (NTRS)

We consider an isolated bubble boiling regime in which vapour bubbles are intermittently produced at a prearranged set of nucleation site on an upward facing overheated wall plane. In this boiling regime, the bubbles depart from the wall and move as separate entities. Except in the matter of rise velocity, the bubbles do not interfere and are independent of one another. However, the rise velocity is dependent on bubble volume concentration in the bulk. Heat transfer properties specific to this regime cannot be described without bubble detachment size, and we apply our previously developed dynamic theory of vapour bubble growth and detachment to determine this size. Bubble growth is presumed to be thermally controlled. Two limiting cases of bubble evolution are considered: the one in which buoyancy prevails in promoting bubble detachment and the one in which surface tension prevails. We prove termination of the isolated regime of pool nucleate boiling to result from one of the four possible causes, depending on relevant parameters values. The first cause consists in the fact that the upward flow of rising bubbles hampers the downward liquid flow, and under certain conditions, prevents the liquid from coming to the wall in an amount that would be sufficient to compensate for vapour removal from the wall. The second cause is due to the lateral coalescence of growing bubbles that are attached to their corresponding nucleation sites, with ensuing generation of larger bubbles and extended vapour patches near the wall. The other two causes involve longitudinal coalescence either 1) immediately in the wall vicinity, accompanied by the establishment of the multiple bubble boiling regime, or 2) in the bulk, with the formation of vapour columns. The longitudinal coalescence in the bulk is shown to be the most important cause. The critical wall temperature and the heat flux density associated with isolated bubble regime termination are found to be functions of the physical and operating parameters and are discussed in detail.

Buyevich, Y. A.; Webbon, Bruce W.; Callaway, Robert (Technical Monitor)

1995-01-01

372

Cavitation behavior of liquid rocket pumps  

SciTech Connect

Liquid rocket pumps were released and tested for obtaining the cavitation and non-cavitation performance. Two pumps, one each for fuel and oxidizer were tested for obtaining the critical Net Positive Suction Head for ensuring the cavitation free operation of these pumps in flight. The experimentally obtained values of NPSH have been compared with the theoretical values obtained using the model developed by Stripling (1962). Based on this comparison it is possible to predict the propellant tank pressure in advance with some confidence. The final value of tank pressure can be revised later when more comprehensive experimental values are available.

Gupta, N.K. [LPSC/ISRO, Trivandrum (India)

1994-12-31

373

Nanosecond laser-induced cavitation in carbon microparticle suspensions - Applications in nonlinear interface switching  

NASA Astrophysics Data System (ADS)

Nanosecond transmission to total internal reflection switching has been demonstrated using a thin absorbing film of carbon microparticles suspended in ethanol. The switching results from laser-induced cavitation and the large refractive index mismatch that occurs when the vapor bubble meets the surrounding glass substrate. This extraordinarily large refractive index change causes the incident beam to be totally internally reflected at the glass-vapor interface. Switching energies below 1 micro-J have been measured using a 5 ns doubled Nd:YAG laser pulse. The effects that particle concentration, film thickness, and bias temperature have on switching performance are investigated.

Lawson, C. M.; Euliss, G. W.; Michael, R. R.

1991-05-01

374

Theoretical modeling of the vapor cavitation in dynamically loaded journal bearings  

NASA Technical Reports Server (NTRS)

A theoretical investigation is made of the evolution of a vapor-bubble for a submerged journal bearing under dynamically loaded conditions using the Elrod algorithm. This method conserves mass throughout the computational domain. A comparison study is performed to determine some of the consequences of applying a nonconservative theory (pseudo-Gumbel BC) to a dynamic problem. A complete dynamic cycle of a journal whirling in a circular path is chosen for the basis of comparison. Significant differences are observed in the load components near the end of the cycle. Further, good agreement with experiment is found for stationary and nonstationary cavitation.

Brewe, D. E.

1985-01-01

375

Spontaneous cavitation in a Lennard-Jones liquid at negative pressures.  

PubMed

We report a molecular dynamics (MD) study of homogeneous bubble nucleation in a Lennard-Jones liquid under a negative pressure (cavitation). The rate of bubble nucleation has been determined in the range 2 x 10(-9) < J(*) = J?(4)(m/?)(1/2) < 6 x 10(-6) by the mean lifetime method at temperatures T(*) = kBT/? = 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.4, 0.5, 0.6, 0.7, 0.8. In molecular dynamics simulation calculations have also been made of the coefficient of bubble size diffusion, the Zeldovich nonequilibrium factor, and the radius of a critical nucleus R*. Different approaches to the determination of the nucleation rate in a stretched liquid have been considered in the framework of classical nucleation theory (CNT). The values of J obtained in MD simulation are by 8-20 orders higher than those predicted by CNT. The work of formation of a critical bubble and the dependence of surface tension ?(R*) at the critical bubble-liquid interface have been determined by data of MD simulation from CNT. The values of ? obtained have been approximated by an extended Tolman formula that takes into account, besides a linear correction, also the quadratic in curvature terms. The Tolman length ?? is negative and equals -(0.1-0.2)?. The coefficient at 1/R*(2) is positive and does not exceed ?(2). PMID:24832287

Baidakov, V G; Bobrov, K S

2014-05-14

376

Spontaneous cavitation in a Lennard-Jones liquid at negative pressures  

NASA Astrophysics Data System (ADS)

We report a molecular dynamics (MD) study of homogeneous bubble nucleation in a Lennard-Jones liquid under a negative pressure (cavitation). The rate of bubble nucleation has been determined in the range 2 × 10^{ - 9} < J^{{kern 1pt} *} = J? ^4 (m/\\varepsilon)^{1/2} < 6 × 10^{ - 6} by the mean lifetime method at temperatures T{kern 1pt} ^* = k_B T/\\varepsilon = 0.35, 0.4, 0.5, 0.6, 0.7, 0.8. In molecular dynamics simulation calculations have also been made of the coefficient of bubble size diffusion, the Zeldovich nonequilibrium factor, and the radius of a critical nucleus R*. Different approaches to the determination of the nucleation rate in a stretched liquid have been considered in the framework of classical nucleation theory (CNT). The values of J obtained in MD simulation are by 8-20 orders higher than those predicted by CNT. The work of formation of a critical bubble and the dependence of surface tension ?(R*) at the critical bubble-liquid interface have been determined by data of MD simulation from CNT. The values of ? obtained have been approximated by an extended Tolman formula that takes into account, besides a linear correction, also the quadratic in curvature terms. The Tolman length ?? is negative and equals -(0.1-0.2)?. The coefficient at 1/R_{{kern 1pt} *}^{{kern 1pt} 2} is positive and does not exceed ?2.

Baidakov, V. G.; Bobrov, K. S.

2014-05-01

377

Water-Splitting Photoelectrolysis Reaction Rate via Microscopic Imaging of Evolved Oxygen Bubbles  

E-print Network

Water-Splitting Photoelectrolysis Reaction Rate via Microscopic Imaging of Evolved Oxygen Bubbles Institute of Technology, Pasadena, California 91125, USA Bubble formation and growth on a water of the gas-evolving reaction rate. Optical microscopy was used to record the bubble growth on single

Atwater, Harry

378

Mesenteric lymph node cavitation in coeliac disease.  

PubMed Central

A patient with coeliac disease and mesenteric lymph node cavitation is reported. This is a rare occurrence and has received very little attention in the English literature. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 PMID:3721297

Holmes, G K

1986-01-01

379

Some Stochastic Aspects of Intergranular Creep Cavitation.  

National Technical Information Service (NTIS)

We present some results obtained from a simplified stochastic model of intergranular creep cavitation. The probabilistic features of the model arise from the inclusion of random cavity placement on the grain boundary and time-discrete stochastic cavity nu...

S. J. Fariborz, J. P. Farris, D. G. Harlow, T. J. Delph

1987-01-01

380

CAVITATIONAL HYDROTHERMAL OXIDATION: A NEW REMEDIATION PROCESS  

EPA Science Inventory

This research will explore the emerging science of sonochemistry and its technological applications for organic waste remediation, particularly for water and soil purification. Ultrasound can induce unusual high-energy chemistry through the process of acoustic cavitation: the for...

381

Microgeometrical cavitation in oscillating slider contacts  

NASA Astrophysics Data System (ADS)

This paper deals with microgeometrically-determined cavitation in oscillating slider bearings. After explaining the difference in the origin of cavitation in journal and linear bearings, the theoretical idea of a computer simulation program on the basis of a combined microhydryodynamic/solid-solid-contact approach is introduced. With the help of this program, slider surface geometry, inertia effects, lubricant properties, normal load, and lubricant film temperatures were found as parameters of microcavitation.

Wietzel, U.

1994-04-01

382

Cavitation Erosion Performance of Fiber Reinforced Composites  

Microsoft Academic Search

The cavitation damage resistance of several fiber reinforced polymeric composite systems was evaluated before and after seawater immersion via a modified ASTM G-32 method utilizing a stationary specimen. For both dry and saturated condi tions, a carbon fiber\\/thermoplastic toughened epoxy matrix composite (IM7\\/977-2T) was found to perform the best under cavitation attack, while carbon fiber\\/thermoplastic matrix (AS4\\/PEEK) was found to

Douglas A. Hammond; Maurice F. Amateau; Richard A. Queeney

1993-01-01

383

Notes 06. Liquid cavitation in fluid film bearings  

E-print Network

condition or Swift-Stieber model) at the leading edge of the cavitation zone are: M x Full film zone dP/dx < 0 ?R journal bearing x Cavitation zone x 1 =R? 1 h * film thickness at cavitation inception ?h * P=P cav Figure 6.4. Cavitation... at the cavitation pressure P cav . Rewrite Eqn (6.13) as ? ? ??? ? ? ? ? = ? ? = PP g cc )/( (6.14) where g is known as a switch function, 1 in full film zone 0 in cavitation zone g ?? = ?? ?? (6.15) Direct integration of equation (6...

San Andres, Luis

2009-01-01

384

Bubble Colloidal AFM Probes Formed from Ultrasonically Generated Bubbles  

E-print Network

Letters Bubble Colloidal AFM Probes Formed from Ultrasonically Generated Bubbles Ivan U. Vakarelski forces between two small bubbles (80-140 µm) in aqueous solution during controlled collisions) was extended to measure interaction forces between a cantilever-attached bubble and surface-attached bubbles

Chan, Derek Y C

385

Chaotic bubbling and nonstagnant foams.  

PubMed

We present an experimental investigation of the agglomeration of bubbles obtained from a nozzle working in different bubbling regimes. This experiment consists of a continuous production of bubbles from a nozzle at the bottom of a liquid column, and these bubbles create a two-dimensional (2D) foam (or a bubble raft) at the top of this column. The bubbles can assemble in various dynamically stable arrangement, forming different kinds of foams in a liquid mixture of water and glycerol, with the effect that the bubble formation regimes influence the foam obtained from this agglomeration of bubbles. The average number of bubbles in the foam is related to the bubble formation frequency and the bubble mean lifetime. The periodic bubbling can generate regular or irregular foam, while a chaotic bubbling only generates irregular foam. PMID:17677349

Tufaile, Alberto; Sartorelli, José Carlos; Jeandet, Philippe; Liger-Belair, Gerard

2007-06-01

386

Electrowetting of soap bubbles  

NASA Astrophysics Data System (ADS)

A proof-of-concept demonstration of the electrowetting-on-dielectric of a sessile soap bubble is reported here. The bubbles are generated using a commercial soap bubble mixture—the surfaces are composed of highly doped, commercial silicon wafers covered with nanometer thick films of Teflon®. Voltages less than 40 V are sufficient to observe the modification of the bubble shape and the apparent bubble contact angle. Such observations open the way to inter alia the possibility of bubble-transport, as opposed to droplet-transport, in fluidic microsystems (e.g., laboratory-on-a-chip)—the potential gains in terms of volume, speed, and surface/volume ratio are non-negligible.

Arscott, Steve

2013-07-01

387

Sensitivity of free radicals production in acoustically driven bubble to the ultrasonic frequency and nature of dissolved gases.  

PubMed

Central events of ultrasonic action are the bubbles of cavitation that can be considered as powered microreactors within which high-energy chemistry occurs. This work presents the results of a comprehensive numerical assessment of frequency and saturating gases effects on single bubble sonochemistry. Computer simulations of chemical reactions occurring inside a bubble oscillating in liquid water irradiated by an ultrasonic wave have been performed for a wide range of ultrasonic frequencies (213-1100kHz) under different saturating gases (O2, air, N2 and H2). For O2 and H2 bubbles, reactions mechanism consisting in 25 reversible chemical reactions were proposed for studying the internal bubble-chemistry whereas 73 reversible reactions were taken into account for air and N2 bubbles. The numerical simulations have indicated that radicals such as OH, H, HO2 and O are created in the bubble during the strong collapse. In all cases, hydroxyl radical (OH) is the main oxidant created in the bubble. The production rate of the oxidants decreases as the driving ultrasonic frequency increases. The production rate of OH radical followed the order O2>air>N2>H2 and the order becomes more remarkable at higher ultrasonic frequencies. The effect of ultrasonic frequency on single bubble sonochemistry was attributed to its significant impact on the cavitation process whereas the effects of gases were attributed to the nature of the chemistry produced in the bubble at the strong collapse. It was concluded that, in addition to the gas solubility, the nature of the internal bubble chemistry is another parameter of a paramount importance that controls the overall sonochemical activity in aqueous solutions. PMID:25112684

Merouani, Slimane; Hamdaoui, Oualid; Rezgui, Yacine; Guemini, Miloud

2015-01-01

388

Planar Soap Bubbles  

Microsoft Academic Search

The generalized soap bubble problem seeks the least perimeter way to enclose\\u000aand separate n given volumes in R^m. We study the possible configurations for\\u000aperimeter minimizing bubble complexes enclosing more than two regions. We prove\\u000athat perimeter minimizing planar bubble complexes with equal pressure regions\\u000aand without empty chambers must have connected regions. As a consequence, we\\u000ashow that

RICHARD PAUL; DEVEREAUX VAUGHN

1998-01-01

389

Fluid-structure interaction in case of water hammer with cavitation  

NASA Astrophysics Data System (ADS)

The transient behavior of liquid-filled pipe systems is studied. The time scale is acoustic. Pressure waves in the liquid, and axial, lateral, and torsional stress waves in the pipes are the dominant phenomena. The phenomena in the liquid (water hammer) and the phenomena in the pipe system (structural dynamic) influence each other if significant radial and axial pipe motions occur. When, in addition, the dynamic pressure drops to the vapor pressure, vapor bubbles will form in the liquid (cavitation). The major new element of the present work is in the simultaneous occurrence of fluid-structure interaction (FSI) and cavitation, which is investigated both theoretically and experimentally. An extensive review of literature on the subject is given. One dimensional basic equations are obtained by integration of general three dimensional equations for fluid dynamics and structural linear elasticity. Three FSI-mechanisms (junction, Poisson, and friction-coupling) are taken into account. The governing equations, formulated as a hyperbolic set of fourteen first-order partial differential equations, are solved by the method of characteristics. Vapor cavitation is numerically simulated by the relatively simple concentrated cavity model.

Tijsseling, A. S.

1993-06-01

390

Radio Bubbles in Clusters  

E-print Network

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with Ghz radio emission, to our sample, and also investigating ``ghost bubbles,'' i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t_cool bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.

R. J. H. Dunn; A. C. Fabian; G. B. Taylor

2005-10-06

391

Removal of Microcystis aeruginosa using hydrodynamic cavitation: performance and mechanisms.  

PubMed

Algal blooms are a seasonal problem in eutrophic water bodies, and novel approaches to algal removal are required. The effect of hydrodynamic cavitation (HC) on the removal of Microcystis aeruginosa was investigated using a laboratory scale device. Samples treated by HC were subsequently grown under illuminated culture conditions. The results demonstrated that a short treatment with HC could effectively settle naturally growing M. aeruginosa without breaking cells. Algal cell density and chlorophyll-a of a sample treated for 10 min were significantly decreased by 88% andv 94%, respectively, after 3 days culture. Various HC operating parameters were investigated, showing that inhibition of M. aeruginosa growth mainly depended on treatment time and pump pressure. Electron microscopy confirmed that sedimentation of algae was attributable to the disruption of intracellular gas vesicles. Damage to the photosynthetic apparatus also contributed to the inhibition of algal growth. Free radicals produced by the cavitation process could be as an indirect indicator of the intensity of HC treatment, although they inflicted minimal damage on the algae. In conclusion, we suggest that HC represents a potentially highly effective and sustainable approach to the removal of algae from water systems. PMID:24960124

Li, Pan; Song, Yuan; Yu, Shuili

2014-10-01

392

Original paper Soap Bubble Clusters  

E-print Network

Original paper Soap Bubble Clusters Fred ALMGREN surface, soap bubbles Abstract. This article reviews the theorems from geometric measure theory which guarantee the existence and give the structure of mathematical models of soap bubble clusters. It also

Taylor, Jean

393

A Bubble Full of Sunshine  

NSF Publications Database

... Release 05-030A Bubble Full of Sunshine Temperatures inside bursting bubbles can be four times ... University of Illinois have determined that temperatures inside gas bubbles collapsing in a liquid ...

394

Prospects for bubble fusion  

SciTech Connect

In this paper a new method for the realization of fusion energy is presented. This method is based on the superhigh compression of a gas bubble (deuterium or deuterium/thritium) in heavy water or another liquid. The superhigh compression of a gas bubble in a liquid is achieved through forced non-linear, non-periodic resonance oscillations using moderate amplitudes of forcing pressure. The key feature of this new method is a coordination of the forced liquid pressure change with the change of bubble volume. The corresponding regime of the bubble oscillation has been called {open_quotes}basketball dribbling (BD) regime{close_quotes}. The analytical solution describing this process for spherically symmetric bubble oscillations, neglecting dissipation and compressibility of the liquid, has been obtained. This solution shown no limitation on the supercompression of the bubble and the corresponding maximum temperature. The various dissipation mechanisms, including viscous, conductive and radiation heat losses have been considered. It is shown that in spite of these losses it is possible to achieve very high gas bubble temperatures. This because the time duration of the gas bubble supercompression becomes very short when increasing the intensity of compression, thus limiting the energy losses. Significantly, the calculated maximum gas temperatures have shown that nuclear fusion may be possible. First estimations of the affect of liquid compressibility have been made to determine possible limitations on gas bubble compression. The next step will be to investigate the role of interfacial instability and breaking down of the bubble, shock wave phenomena around and in the bubble and mutual diffusion of the gas and the liquid.

Nigmatulin, R.I. [Tyumen Institute of Mechanics of Multiphase Systems (TIMMS), Marx (Russian Federation); Lahey, R.T. Jr. [Rensselaer Polytechnic Institute, Troy, NY (United States)

1995-09-01

395

Radial oscillation of a gas bubble in a fluid as a problem in canonical perturbation theory  

NASA Astrophysics Data System (ADS)

The oscillation of a gas bubble is in a fluid is of interest in many areas of physics and technology. Lord Rayleigh treated the pressure developed in the collapse of cavitation bubbles and developed an expression for the collapse period. Minnaert developed a harmonic oscillator approximation to bubble oscillation in his study of the sound produced by running water. Oscillating bubbles are important to oceanographers studying the sound spectrum produced by water waves, geophysicists employing air guns as acoustic probes, mechanical engineers concerned with erosion of turbine blades, and military engineers concerned with the acoustic signatures developed by the propeller screws of ships and submarines. For the oceanographer, Minnaert's approximation is useful, for the latter two examples, Lord Rayleigh's analysis is appropriate. On the one hand, a bubble can be treated as a harmonic oscillator in the small amplitude regime, whereas even in the relatively moderate pressure regime characteristic of air guns the oscillation is strongly nonlinear and amplitude dependent. Is it possible to develop an analytic approximation that affords insight into the behavior of a bubble beyond the harmonic approximation of Minnaert? In this spirit, the free radial oscillation of a gas bubble in a fluid is treated as a problem in canonical perturbation theory. Several orders of the expansion are determined in order to explore the dependence of the oscillation frequency with bubble amplitude. The expansion to second order is inverted to express the time dependence of the oscillation.

Stephens, James

2005-11-01

396

CHARACTERISTICS OF THE SECONDARY BUBBLE CLUSTER PRODUCED BY AN ELECTROHYDRAULIC SHOCK WAVE LITHOTRIPTER  

PubMed Central

This study investigated the characteristics of the secondary bubble cluster produced by an electrohydraulic lithotripter using high-speed imaging and passive cavitation detection techniques. The results showed that (i) the discrepancy of the collapse time between near a flat rigid boundary and in a free field of the secondary bubble cluster was not as significant as that by the primary one; (ii) the secondary bubble clusters were small but in a high bubble density and nonuniform in distribution, and they did not expand and aggregate significantly near a rigid boundary; and (iii) the corresponding bubble collapse was weaker with few microjet formation and bubble rebound. By applying a strong suction flow near the electrode tip, the production of the secondary shock wave (SW) and induced bubble cluster could be disturbed significantly, but without influence on the primary ones. Consequently, stone fragmentation efficiency was reduced from 41.2 ± 7.1% to 32.2 ± 3.5% after 250 shocks (p <0.05). Altogether, these observations suggest that the secondary bubble cluster produced by an electrohydraulic lithotripter may contribute to its ability for effective stone fragmentation. PMID:22390990

Zhou, Yufeng; Qin, Jun; Zhong, Pei

2013-01-01

397

Free-Lagrange simulations of the expansion and jetting collapse of air bubbles in water  

NASA Astrophysics Data System (ADS)

A free-Lagrange numerical method is implemented to simulate the axisymmetric jetting collapse of air bubbles in water. This is performed for both lithotripter shock-induced collapses of initially stable bubbles, and for free-running cases where the bubble initially contains an overpressure. The code is validated using two test problems (shock-induced bubble collapse using a step shock, and shock10 MPa tensile waves, interacts with a bubble of initial radius 0.04 mm located in a free field (case 1) and near a rigid boundary (case 2). The interaction of the shock with the bubble causes it to involute and a liquid jet is formed that achieves a velocity exceeding 1.2 km s1 for case 2. The impact of the jet on the downstream wall of the bubble generates a blast wave with peak overpressure exceeding 1 GPa and 1.75 GPa for cases 1 and 2, respectively. The results show that the simulation technique retains sharply resolved gas/liquid interfaces regardless of the degree of geometric deformation, and reveal details of the dynamics of bubble collapse. The effects of compressibility are included for both liquid and gas phases, whereas stress distributions can be predicted within elastic-plastic solid surfaces (both planar and notched) in proximity to cavitation events. There is a movie with the online version of the paper.

Turangan, C. K.; Jamaluddin, A. R.; Ball, G. J.; Leighton, T. G.

398

Feedback loop process for controlling inertial cavitation: experimental evidence  

NASA Astrophysics Data System (ADS)

Applications involving cavitation mechanisms, such as sonoporation, are irreproducible in the case of a fixed-intensity sonication, due to the non-stationary behavior of cavitation. We then propose to work at a fixed-cavitation level instead of under fixed-intensity sonication conditions. For this purpose a regulated cavitation generator has been developed in a stationary wave field configuration, which allows regulation of the cavitation level during sonication by modulating the applied acoustic intensity with a feedback loop based on acoustic cavitation measurements. The cavitation level indicator was quantified by the broadband spectrum noise level relative to inertial cavitation events. This generated inertial cavitation was characterized by both acoustic and chemical measurements, quantifying hydroxyl radicals produced by water sonolysis. While the cavitation level is obtained with a 40% standard deviation for fixed applied acoustic intensities in the range [0.01 3.44] W/cm2, the regulated generator reproduces the cavitation level with a standard deviation of 3%. The results show that the hydroxyl radical production is better correlated with the cavitation level setting than with the applied acoustic intensity, highlighting the fact that broadband noise is a good indicator of inertial cavitation, with greatest interest for cavitation monitoring. In summary, the regulated device generates a cavitation level that is reproducible, repeatable and stable in time. This system produces reproducible effects that allow consideration of biological applications such as sonoporation to be independent of the experimental ultrasound device, as confirmed by transfection efficiency and cell cytotoxicity studies. Thus, this feedback loop process presents interesting perspectives for monitoring and controlling in-vivo cavitation.

Inserra, Claude; Sabraoui, Abbas; Reslan, Lina; Bera, Jean-Christophe; Gilles, Bruno; Mestas, Jean-Louis

2011-09-01

399

Study of non-spherical bubble oscillations near a surface in a weak acoustic standing wave field.  

PubMed

The interaction of acoustically driven bubbles with a wall is important in many applications of ultrasound and cavitation, as the close boundary can severely alter the bubble dynamics. In this paper, the non-spherical surface oscillations of bubbles near a surface in a weak acoustic standing wave field are investigated experimentally and numerically. The translation, the volume, and surface mode oscillations of bubbles near a flat glass surface were observed by a high speed camera in a standing wave cell at 46.8?kHz. The model approach is based on a modified Keller-Miksis equation coupled to surface mode amplitude equations in the first order, and to the translation equations. Modifications are introduced due to the adjacent wall. It was found that a bubble's oscillation mode can change in the presence of the wall, as compared to the bubble in the bulk liquid. In particular, the wall shifts the instability pressure thresholds to smaller driving frequencies for fixed bubble equilibrium radii, or to smaller equilibrium radii for fixed excitation frequency. This can destabilize otherwise spherical bubbles, or stabilize bubbles undergoing surface oscillations in the bulk. The bubble dynamics observed in experiment demonstrated the same trend as the theoretical results. PMID:25234973

Xi, Xiaoyu; Cegla, Frederic; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander

2014-04-01

400