Role Of Cavitation Research Articles

The role of cavitation in the toughening of elastomer nanocomposites reinforced with graphene nanoplatelets

The toughening of different types of elastomers through the incorporation of graphene nanoplatelets (GNPs) has been investigated. Both the tear strength and tearing energy are increased significantly through a combination of mechanisms such as debonding, pull-out and cavitation. The processes that occur ahead of a tear/crack tip in natural rubber filled with GNPs have been monitored in situ using synchrotron-based nanoscale X-ray computed tomography. The GNP particles are found to debond and form voids that grow under stress leading to considerable energy absorption. The mechanisms of cavitation and void growth are analysed theoretically and it is shown that voids need to be larger than ∼1 μm in size to grow in the triaxial tensile stress field ahead of the tear/crack tip. The high level of cavitation and void growth found for the elastomers filled with micron-sized GNP particles is suggested to be the reason why these nanocomposites have a high tear resistance.

The role of cavitation and gas bubbles in the non-photochemical laser-induced nucleation of sodium acetate

Laser pulse nucleates anhydrous sodium acetate and stable gas bubbles from solution.

Interdependence of Tissue Temperature, Cavitation, and Displacement Imaging During Focused Ultrasound Nerve Sonication.

Focused ultrasound (FUS) peripheral neuromodulation has been linked to nerve displacement caused by the acoustic radiation force; however, the roles of cavitation and temperature accumulation on nerve modulation are less clear, as are the relationships between these three mechanisms of action. Temperature directly changes tissue stiffness and viscosity. Viscoelastic properties have been shown to affect cavitation thresholds in both theoretical and ex vivo models, but the direct effect of temperature on cavitation has not been investigated in vivo. Here, cavitation and tissue displacement were simultaneously mapped in response to baseline tissue temperatures of either 30 °C or 38 °C during sciatic nerve sonication in mice. In each mouse, the sciatic nerve was repeatedly sonicated at 1.1-MHz, 4-MPa peak-negative pressure, 5-ms pulse duration, and either 15- or 30-Hz pulse repetition frequency (PRF) for 10 s at each tissue temperature. Cavitation increased by 1.8-4.5 dB at a tissue temperature of 38 °C compared to 30 °C, as measured both by passive cavitation images and cavitation doses. Tissue displacement also increased by 1.3- [Formula: see text] at baseline temperatures of 38 °C compared to 30 °C. Histological findings indicated small increases in red blood cell extravasation in the 38 °C baseline temperature condition compared to 30 °C at both PRFs. A strong positive correlation was found between the inertial cavitation dose and displacement imaging noise, indicating the potential ability of displacement imaging to simultaneously detect inertial cavitation in vivo. Overall, tissue temperature was found to modulate both in vivo cavitation and tissue displacement, and thus, both tissue temperature and cavitation can be monitored during FUS to ensure both safety and efficiency.

On the path from xylem hydraulic failure to downstream cell death.

Xylem hydraulic failure (HF) has been identified as a ubiquitous factor in triggering drought-induced tree mortality through the damage induced by the progressive dehydration of plant living cells. However, fundamental evidence of the mechanistic link connecting xylem HF to cell death has not been identified yet. The main aim of this study was to evaluate, at the leaf level, the relationship between loss of hydraulic function due to cavitation and cell death under drought conditions and discern how this relationship varied across species with contrasting resistances to cavitation. Drought was induced by withholding water from potted seedlings, and their leaves were sampled to measure their relative water content (RWC) and cell mortality. Vulnerability curves to cavitation at the leaf level were constructed for each species. An increment in cavitation events occurrence precedes the onset of cell mortality. A variation in cells tolerance to dehydration was observed along with the resistance to cavitation. Overall, our results indicate that the onset of cellular mortality occurs at lower RWC than the one for cavitation indicating the role of cavitation in triggering cellular death. They also evidenced a critical RWC for cellular death varying across species with different cavitation resistance.

Coronary artery cavitation as a trigger for atherosclerotic plaque progression: a numerical and computational fluid dynamic demonstration

Abstract Background Coronary cavitation is supposed to be generated by both concentric and eccentric coronary artery stenosis creating microbubbles which exploded when the fluid pressure was lower than the vapor pressure at a local thermodynamic state. Aims To assess, using computational fluid dynamic analysis (CFD), the potential role of cavitation in inducing coronary artery endothelial damage and promote atherosclerotic plaque progression. Methods We retrospectively reviewed the procedural records of consecutive patients evaluated between 1st January 2013 and 1st January 2014 with an isolated hemodynamically significant Left Main (LM) disease. Each bifurcation was reconstructed on the patient-specific geometries derived from the CCTA applying patient-specific hemodynamic features. Vapour has been modelled as discrete vapour bubbles and its trajectory determined using a Lagrangian frame of reference. Cavitation started with micro-cavitation nuclei which subsequently grow into bubbles undergoing different physical processes determined in a stochastic Monte-Carlo approximation. Results Among the 12 patients analysed [8 males, mean age 68.2±12.8 years old], the mean LM stenosis was 72.3±3.6%. In all subjects, LM stenoses induced cavitation which propagates downstream the vessel. The higher concentration of vapour region was detected before the carina (within 0.8 to 1.3 cm from the stenosis). The mean bubbles radius observed before the carina was 4.2±1.4 μm; their impact with the endothelial surface generated a mean peak pressure of 3.9±0.5 MPa determining a local shockwave (Figure 1). Conclusion The collapse of micro-bubbles alongside the endothelium generated micro-shockwaves determining repeated dynamic load measurable as an instantaneous pressure-peaks able to induce endothelial injury or dysfunction. Funding Acknowledgement Type of funding sources: None. Figure 1. (A) The simulation illustrates the vapour fraction iso-surfaces and the scattered bubble plots as predicted by the Langrangian model. Notably, most cavitation bubbles that form at the inlet of left main bifurcation do not collapse immediately but they are transported towards the vessel determining several interactions with the endothelium. (B) Graphical representation of the bubble radius modification and related pressure transmitted to the endothelium if the bubble collapse happened near to this last one. The magnification in boxes (B1-B4) evidences the dynamic modification of bubbles. The re-entry jet causing the collapse is evidenced with a red arrow.

Melting temperature changes during slip across subglacial cavities drive basal mass exchange

AbstractThe importance of glacier sliding has motivated a rich literature describing the thermomechanical interactions between ice, liquid water and bed materials. Early recognition of the gradient in melting temperature across small bed obstacles led to focused studies of regelation. An appreciation for the limits on ice deformation rates downstream of larger obstacles highlighted a role for cavitation, which has subsequently gained prominence in descriptions of subglacial drainage. Here, we show that the changes in melting temperature that accompany changes in normal stress along a sliding ice interface near cavities and other macroscopic drainage elements cause appreciable supercooling and basal mass exchange. This provides the basis of a novel formation mechanism for widely observed laminated debris-rich basal ice layers.

Does Cavitation Affect Droplet Breakup in High‐Pressure Homogenization? Insights into Local Effects

AbstractHigh‐pressure homogenization is a popular method to produce emulsions of droplet sizes smaller than 1 µm. Regarding the role of cavitation in the process, it is still discussed controversially whether it promotes or hinders droplet breakup during high‐pressure homogenization. In this study droplet breakup in a cavitating flow of an optically accessible high‐pressure homogenizer orifice is visualized using a high‐speed camera setup. The cavitation regime is characterized using laser light induced luminescence. Droplet deformation and breakup events are compared to a cavitation‐free flow with the same specific energy input. Once the jet cavitation regime is reached, droplet breakup took place further downstream the orifice exit, and the larger droplets are measured in the final product.

Effect of cavitation intensity control on self-assembling of alkanethiols on gold in room temperature ionic liquids

This study investigates the effect of cavitation intensity on self-assembling of alkanethiol molecules on gold in room temperature ionic liquids (RTILs) under low frequency ultrasound irradiation (20 kHz). The use of RTILs, with low vapor pressure, enabled cavitation activity to be controlled up to quenching through pressure decrease within an argon-saturated atmosphere. This control possibility was used to acquire deeper insights into the role of cavitation on self-assembling processes. It was shown by electrochemical, contact angles and Polarization Modulation - Infrared Reflection Absorption Spectroscopy (PM-IRRAS) measurements that cavitation activates orientation and organization of self-assembled monolayers (SAM). X-ray Photoelectron Spectroscopy (XPS) revealed that, even if chemical adsorption of molecules is highly activated under ultrasound irradiation, it is not dependent on acoustic cavitation intensity.

The Role of Cavitation in Energy Delivery and Stone Damage During Laser Lithotripsy.

Purpose: Although cavitation during laser lithotripsy (LL) contributes to the Moses effect, the impact of cavitation on stone damage is less clear. Using different laser settings, we investigate the role of cavitation bubbles in energy delivery and stone damage. Materials and Methods: The role of cavitation in laser energy delivery was characterized by using photodetector measurements synced with high-speed imaging for laser pulses of varying durations. BegoStone samples were treated with the laser fiber oriented perpendicularly in contact with the stone in water or in air to assess the impact of cavitation on crater formation. Crater volume and geometry were quantified by using optical coherence tomography. Further, the role of cavitation in stone damage was elucidated by treatment in water with the fiber oriented parallel to the stone surface and by photoelastic imaging. Results: Longer pulse durations resulted in higher energy delivery but smaller craters. Stones treated in water resulted in greater volume, wider yet shallower craters compared with those treated in air. Stones treated with the parallel fiber showed crater formation after 15 pulses, confirmed by high-speed imaging of the bubble collapse with the resultant stress field captured by photoelastic imaging. Conclusions: Despite improved energy delivery, the longer pulse mode produced smaller crater volume, suggesting additional processes secondary to photothermal ablation are involved in stone damage. Our critical observations of the difference in stone damage treated in water vs in air, combined with the crater formation by parallel fiber, suggest that cavitation is a contributor to stone damage during LL.

Modeling of Tertiary Creep in Copper at 215 and 250 °C

AbstractFor a long time, only empirical models existed for creep curves in the tertiary stage. To understand the role of creep damage, including changes in the dislocation structure, cavitation, and necking, basic models that do not involve adjustable parameters have, however, recently been developed. These models were used to predict tertiary creep for copper at 75 °C. In the present paper, these models are applied to creep tests at higher temperatures (215 and 250 °C). These results demonstrate again that tertiary creep in copper is primarily controlled accelerated recovery of the dislocation structure and not by cavitation. The modeling results suggest that the role of cavitation is modest also in other creep exposed ductile alloys, which should be of importance to consider in the formulation of models for creep damage. Necking was only found to be of significance very close to rupture again in agreement with results at lower temperature.

Preface

The Anglo-French Physical Acoustics Conference (AFPAC) 2020 meeting at Selsdon Park was held from 15 to 17 January 2020. As it is now a very recognisable characteristic of this meeting, the range of acoustics/ultrasound topics covered was quite impressive. Over the three days of the conference, 40 high quality papers were presented by speakers at different stages of their research careers, from those still at the early stages of their PhD projects, to well-established world leaders in the field. From amongst the latter category we had seven invited speakers: Carmel Moran (translational ultrasound); Brian Fowlkes (bubbles and droplets in medical applications); Ana Namburete (ultrasound imaging of foetal brain development); Richard Craster (elastic meta-materials); Vincent Pagneux (observation of topological edge waves); Larry Crum (role of cavitation in therapeutic ultrasound) and Quentin Grimal (ultrasound evaluation of bone fragility). We were all very grateful for the knowledge and experience imparted by our invited speakers to all those present. The first day of the meeting was organised jointly with the Medical Physics Group of the IOP, and we would like to say a big thank you to Professor Sarah Bohndiek for her help with the organisation of the event. We are also grateful to Verasonics Ltd. and Carlos Faustmann for their sponsorship of the meeting.Nader SaffariAlain LhemeryFrederic CeglaTony Valier-Brasier

Generation of a Fine Aerosol in a Cavitation Regime

Consideration is given to the problem of atomization of fine aerosols using atomizers of special designs that implement a cavitation regime. The formation of a fine aerosol is studied with the model of a pulse atomizer utilizing HEM energy and the model of an atomizer with a special nozzle to create counterflows. For these atomizers, the role of cavitation in obtaining a fine liquid aerosol is shown. A mathematical model is proposed which describes the processes of genesis of an aerosol cloud. Estimates of the critical pressure are obtained for the development of cavitation, the outflow velocity, and the resulting size of droplets as functions of the geometric parameters of the atomizers, the pressure in the structure, and the physicochemical properties of the liquid. Experimental investigations of the dispersion and concentration of aerosol particles are carried out using optical methods of measurement. Results of measuring the dispersion parameters of an aerosol in the process of cavitation atomization of liquids are presented.

Effect of UV-aging on the mechanical and fracture behavior of low density polyethylene

In polyethylene, a transient, oxidation-induced strengthening is often observed over a narrow range of UV radiation dose. In addition, plastic deformation may not be volume-preserving due to cavitation. Here, we employ a suite of analytical experiments and mechanical testing on pristine and oxidized low-density polyethylene films in order to investigate the transient strengthening behavior as well as the propensity for cavitation to fracture. Emphasis is laid on connecting macroscopically observed behavior with microscopic information involving the competition between multi-scale phenomena: chain scission and cross linking at a fine scale, chemi-crystallization, oxidation-induced cracking and mechanical damage at the meso and coarse scales. The results provide an insight into the role of cavitation in the oxidative embrittlement of semicrystalline polymers.

Effects of 20 kHz ultrasound on coal flotation: The roles of cavitation and acoustic radiation force

Cavitation and acoustic radiation force are two main effects of ultrasound. In this study, ultrasonic pretreatment (UPT) and simultaneous treatment (UST) methods were applied to coal flotation. The ultrasonic effects were analyzed by measuring changes in ash content and yield of concentrate with or without ultrasound treatment. The decrease in ash content after UPT or UST was due to the cleaning effect of ultrasound. This effect is generated by the collapse of tiny bubbles trapped on the rough coal surfaces, as seen in images obtained by scanning electron microscopy (SEM). An improvement in recovery was only seen with the UST method. Properties of large bubbles, specifically their aggregation and shape, were influenced by ultrasound through the oscillation behavior and acoustic radiation force in the sound field, respectively. This work is expected to provide a novel perspective to the study of ultrasound-assisted flotation.

The role of cavitation in submicron aerosol dispersion

Here we discuss the problem of atomizing submicron aerosols by special design atomizers enabling the cavitation regime. The formation of submicron aerosol was studied using an impulse atomizer model powered by a high-energy material and an atomizer model with a special spray nozzle generating countercurrent flows. For these atomizers, the role played by cavitation in producing submicron liquid aerosols is demonstrated herein. A mathematical model is also suggested to describe the aerosol cloud genesis. The cavitation development critical pressure, outflow velocity, and the resulting droplet sizes were evaluated. The aerosol particle size and concentration were experimentally measured by optical methods. The measured disperse parameters of aerosols during the origination and propagation of the aerosol cloud resulted from the cavitation-assisted atomization of liquids are reported: the intrinsic particle diameter of water aerosol is 10…30 μm depending on the features of the atomizer designs and their operating regimes.

Prediction of tensile power law creep constants from compression and bend data for ZrB2\u201320 vol% SiC composites at 1800 \xb0C

Here we consider our four-point flexure and compression creep results obtained under Ar protection at 1800 °C to predict the tensile creep behavior of a ZrB2–20 vol% SiC ultra-high temperature ceramic. Assuming power law creep, and based on four-point bend data, we estimated the uniaxial creep parameters using an analytical method present in the literature. Both predicted and experimental compressive stress exponents were found to be in excellent agreement, 1.85 and 1.76 respectively, while observation of the microstructure suggested a combination of diffusion and grain boundary sliding creep mechanisms in compression. Along with the microstructural evidence associated with the tensile regions of the flexure specimens, the predicted tensile stress exponent of 2.61 exceeds the measured flexural value of 2.2. We assert an increasing role of cavitation to the creep strain in pure tension. This cavitation component adds to the dominant grain boundary sliding mechanism as described below and elsewhere for flexural creep.

Modeling of hydraulic fracturing in ultra-low permeability formations: The role of pore fluid cavitation

Hydraulic Fracturing (HF) refers to the process of nucleation and growth of tensile fractures in a reservoir formation by means of flow-induced pressurization. The processes in the fracture process zone (FPZ) of a fluid-driven fracture involve a non-linear coupling between fracturing-fluid flow, rock deformation and diffusion of pore fluid. Identifying all the key physical processes is critical for reliably modeling and simulating fluid-driven fractures. The role of cavitation and subsequent alteration in pore fluid saturation is often ignored in hydraulic fracturing simulations, i.e., the pore fluid is modeled to be able to sustain arbitrarily large negative pressures without undergoing cavitation. Using multi-physics Finite Element Analyses (FEA), we show that ignoring cavitation may lead to spurious outcomes in FEA simulations of fluid-driven fractures in ultra-low permeability formations. The FEA simulations, in the absence of cavitation, predict an unrealistically large suction (negative pressure) ahead of the crack tip, which grows without bound upon refinement of the FEA mesh. Owing to such a large suction at the crack tip, the breakdown pressure obtained from the FEA simulations is anomalously large and lacks objectivity (i.e., progressively increases upon a continued refinement of the FEA mesh). Mechanistic insights gained from FEA simulations suggest that the negative pressure ahead of the crack tip is likely to cause cavitation of the pore fluid, resulting in creation of a partially-saturated region around the crack tip. This means that irrespective of the initial saturation of the rock, inclusion of cavitation and subsequent alteration in pore fluid saturation in FEA simulations is necessary for objectively modeling the fluid-driven fractures in ultra-low permeability formations. The revised FEA simulations of hydraulic fracturing show that the inclusion of cavitation and subsequent alteration in pore fluid saturation in FEA simulations eliminates the unrealistically large suction at the crack tip, regularizes the breakdown pressure, and removes the noted lack of objectivity.

The role of cavitation in vascular occlusion

Ed Carstensen’s papers on the effects of ultrasound on plants were amongst the first that attracted me to study ultrasound bio-effects. It was little surprise to me that, when I first started looking at HIFU, his name was on many of the seminal papers in this area. And now, his papers on cavitation and vasculature inform our current research. Ed’s influence on bio-effects research stretches far beyond the borders of the USA Vascular occlusion has the potential to treat life-threatening conditions including twin-twin transfusion syndrome (occurring in fetuses that share a placenta). Sheep placental vessels have been used to develop HIFU treatment guidance, delivery (1.66MHz) and monitoring. Ultrasound imaging guidance/flow monitoring, with simultaneous acoustic cavitation detection in 82 targets in 14 pregnant sheep resulted in flow occlusion in 90%. Adverse events included skin erythema (18/82) and burns (10/82), but all resolved over 21 days. Analysis of acoustic cavitation required low pass (software) filtering and careful choice of broadband integration range (0.1 to 1.1 MHz). 9% of successful treatments displayed detectable broadband, 32% with half-harmonic and 1% with drive-voltage fluctuations. In conclusion, treatment is possible, side effects are manageable, and acoustic cavitation appears not to be essential for successful occlusion.

Ultrasound-enhanced penetration through sclera depends on frequency of sonication and size of macromolecules

We previously employed ultrasound as a needleless approach to deliver macromolecules via the transscleral route to the back of the eye in live animals (Suen et al., 2013). Here, we investigated the nature of the ultrasound-enhanced transport through sclera, the outermost barrier in the transscleral route. Thus, the possible role of cavitation from ultrasound was explored; its effect during and after sonication on scleral penetration was measured; and the dependence on the size of macromolecules was determined. We applied ultrasound frequency from 40kHz to 3MHz at ISATA (spatial-average-temporal-average intensity) of 0.05W/cm2 to fresh rabbit sclera ex vivo. Fluorescent dextran of size 20kDa to 150kDa was used as macromolecular probes. We measured the distance of penetration of the probes through the sclera over 30s during sonication and over 15min after sonication from cryosectioned tissue images. Deeper penetration in the sclera was observed with decreasing frequency. The presence of stable cavitation was further verified by passive acoustic detection. The effect during sonication increased penetration distance up to 20 fold and was limited to macromolecular probes ≤70kDa. The effect post sonication increased penetration distance up to 3 fold and attributed to the improved intrasscleral transport of macromolecules ≥70kDa. Post-sonication enhancement diminished gradually in 3h. As the extent of cavitation increased with decreasing frequency, the trend observed supports the contribution of (stable) cavitation to enhancing transport through sclera. Effect during sonication was attributed to flow associated with acoustic microstreaming. Effect post sonication was attributed to the temporary increase in scleral permeability. Flow-associated effect was more pronounced but only applied to smaller macromolecules.

Ultrasonic atomization of liquids in drop-chain acoustic fountains.

When focused ultrasound waves of moderate intensity in liquid encounter an air interface, a chain of drops emerges from the liquid surface to form what is known as a drop-chain fountain. Atomization, or the emission of micro-droplets, occurs when the acoustic intensity exceeds a liquid-dependent threshold. While the cavitation-wave hypothesis, which states that atomization arises from a combination of capillary-wave instabilities and cavitation bubble oscillations, is currently the most accepted theory of atomization, more data on the roles of cavitation, capillary waves, and even heat deposition or boiling would be valuable. In this paper, we experimentally test whether bubbles are a significant mechanism of atomization in drop-chain fountains. High-speed photography was used to observe the formation and atomization of drop-chain fountains composed of water and other liquids. For a range of ultrasonic frequencies and liquid sound speeds, it was found that the drop diameters approximately equalled the ultrasonic wavelengths. When water was exchanged for other liquids, it was observed that the atomization threshold increased with shear viscosity. Upon heating water, it was found that the time to commence atomization decreased with increasing temperature. Finally, water was atomized in an overpressure chamber where it was found that atomization was significantly diminished when the static pressure was increased. These results indicate that bubbles, generated by either acoustic cavitation or boiling, contribute significantly to atomization in the drop-chain fountain.