Role Of Cavitation Research Articles

The role of cavitation in the induction of cellular DNA damage by ultrasound and lithotripter shock waves in vitro

The induction of DNA strand breaks in Chinese hamster ovary cells was measured with the comet assay after continuous wave ultrasound or lithotripter shock wave exposure. Cell lysis and hydrogen peroxide production were measured to gauge the level of inertial cavitation activity. Significant DNA damage was found after 2.17-MHz ultrasound exposure at 37°C to 0.82 MPa for 2 min or 4 min, and to 0.58 MPa for 4 min. A significant portion of the damage induced at the 0.82-MPa level was repaired by the cells when warmed. Neither exposure to 500 or 1000 shock waves at 37°C in a thin-walled tube, nor exposure to 1000, 1500 or 2000 shock waves at 25°C in a polyethylene pipette bulb produced a significant effect, when the flash of light from the spark-gap discharge was blocked. This finding was consistent with the generally lower lysis and hydrogen peroxide production by the shock wave exposure.

Mechanisms of Meniscal Tissue Ablation by Short Pulse Laser Irradiation

A new experimental technique was developed to study short-pulsed laser ablation of biologic tissues (human meniscus and bovine tibial bone), water, and acrylic. The experimental technique was based on interferometric monitoring of the motion of the tissue surface to measure its laser-induced expansion after irradiation. The thermoelastic expansion of these materials after laser irradiation under subablation threshold was examined to determine its role in the initiation of ablation. The experimentally observed surface expansion of cortical bone and acrylic was in agreement with theoretical predictions. The movement of meniscal tissue was similar to that shown by water. The latter 2 materials showed additional features consistent with the growth and collapse of cavitation bubbles. The exact role of cavitation in the irradiation of meniscal tissue by laser light remains unknown, but may represent a clinically important mode of tissue ablation and postirradiation trauma.

Microbial cell disruption: role of cavitation

A novel technique of using hydrodynamic cavitation for the large-scale disruption of yeast cells is described. Baker's yeast and brewer's yeast cells in a pressed yeast form were used. Cell disruption was monitored in the form of increase in soluble protein content. Disruption by hydrodynamic cavitation is compared with that obtained by established techniques such as blade blender and acoustic cavitation (ultrasonication). The effect of cell concentration, time of treatment and number of passes in the flow loop system on the extent of cell disruption is reported. The energy efficiency of the hydrodynamic cavitation setup is compared with that of established techniques. Hydrodynamic cavitation was found to be at least an order of magnitude more energy efficient than established techniques such as ultrasonication or blade blender (mixer).

On the role of cavitation in particle collection during flotation - a critical review

This paper reviews the fundamentals of recently developed flotation devices, and a new mechanism of particle collection by cavitation/gas nucleation is proposed. It is shown by both theoretical analysis and practical applications that cavitation/gas nucleation accelerates particle-bubble attachment and flotation rates, and offers a means of improving flotation cell designs. A two-stage attachment model is emphasised and used as a possible explanation of the fast flotation rates achieved by some recently developed flotation cells. While the first stage, i.e., the generation of gas nuclei/cavities and their attachment to particle surfaces can be intensified by stirring, high dissolved gas content in the slurry and hydrodynamic cavitation, the second stage, i.e., the capture of the gas nuclei-activated particles by conventional flotation-sized bubbles can be enhanced by high gas holdups and quiescent flow conditions.

Medical applications and bioeffects of extracorporeal shock waves

Lithotripter shock waves are pressure pulses of microsecond duration with peak pressures of 35–120 MPa followed by a tensile wave. They are an established treatment modality for kidney and gallstone disease. Further applications are pancreatic and salivary stones, as well as delayed fracture healing. The latter are either on their way to become established treatments or are currently under investigation. Shock waves generate tissue damage as a side effect which has been extensively investigated in the kidney, the liver, and the gallbladder. The primary adverse effects are local destruction of blood vessels, bleedings, and formation of blood clots in vessels. Investigations on the mechanism of shock wave action revealed that lithotripters generate cavitation both in vitro and in vivo. An increase in tissue damage at higher pulse administration rates, and also at shock wave application with concomitant gas bubble injection suggested that cavitation is a major mechanism of tissue damage. Disturbances of the heart rhythm and excitation of nerves are further biological effects of shock waves; both are probably also mediated by cavitation. On the cellular level, shock waves induce damage to cell organelles; its extent is related to their energy density. They also cause a transient increase in membrane permeability which does not lead to cell death. Administered either alone or in combination with drugs, shock waves have been shown to delay the growth of small animal tumors and even induce tumor remissions. While the role of cavitation in biological effects is widely accepted, the mechanism of stone fragmentation by shock waves is still controversial. Cavitation is detected around the stone and hyperbaric pressure suppresses fragmentation; yet major cracks are formed early before cavitation bubble collapse is observed. The latter has been regarded as evidence for a direct shock wave effect.

Effects of material anisotropy and inhomogeneity on cavitation for composite incompressible anisotropic nonlinearly elastic spheres

The effects of material anisotropy and inhomogeneity on void nucleation and growth in incompressible anisotropic nonlinearly elastic solids are examined. A bifurcation problem is considered for a composite sphere composed of two arbitrary homogeneous incompressible nonlinearly elastic materials which are transversely isotropic about the radial direction, and perfectly bonded across a spherical interface. Under a uniform radial tensile dead-load, a branch of radially symmetric configurations involving a traction-free internal cavity bifurcates from the undeformed configuration at sufficiently large loads. Several types of bifurcation are found to occur. Explicit conditions determining the type of bifurcation are established for the general transversely isotropic composite sphere. In particular, if each phase is described by an explicit material model which may be viewed as a generalization of the classic neo-Hookean model to anisotropic materials, phenomena which were not observed for the homogeneous anisotropic sphere nor for the composite neo-Hookean sphere may occur. The stress distribution as well as the possible role of cavitation in preventing interface debonding are also examined for the general composite sphere.

Fracture behaviour of Cu-Zn-Co and Cu-Zn-Ni alloys during superplastic deformation

Cavitation and fracture behaviour in two commercial α/gb brasses, one modified with 2wt% Co (Cu-Zn-Co) and the other with 2wt% Cr (Cu-Zn-Cr), have been investigated in Region II of superplastic flow. These alloying elements form cobalt-rich (0.3 μm average diameter) and chromium-rich (5 μm average diameter) precipitate particles which are distributed uniformly in the matrix and which play an important role in cavitation and inhibiting grain growth during deformation. Void size distributions, volume fraction of voids and the number of voids per unit area have been measured as a function of strain in Region II and the results show a very marked difference in the degree of cavitation in Cu-Zn-Co and Cu-Zn-Cr alloys. Experiments show that the deformation is quasi-uniform with little or no necking in the specimens of Cu-Zn-Co alloy in Region II, and the final fracture occurred by the growth and interlinkage of internal voids. On the other hand, in the specimens of Cu-Zn-Cr alloy a sharp or localized neck developed early in the deformation in Region II and the specimen pulled down to a fine point leading to failure by necking. The importance of diffusion or slip accommodation of grain boundary sliding in void formation during superplastic flow is discussed and a criterion for failure is suggested.

Ultrasound and root canal treatment: the need for scientific evaluation.

Summary. Ultrasound has recently been introduced into endodontics to aid in the biomechanical preparation of the root canal. Although there are numerous investigations into the clinical efficacy of the endosonic system, there has been a poor understanding of the possible role of the biophysical aspects of ultrasound. Such areas where clarification is required are the possible roles of cavitation and acoustic microstreaming together with the ‘synergistic’ effect of the combined use of ultrasound and irrigant (usually sodium hypochlorite). Furthermore the oscillation of the file within the root canal may be prone to the load applied to it and this will greatly affect its efficiency. The present article aims to clarify these areas and to provide a guide to some of the biophysical terms used within the ultrasound discipline. Further investigations are required however to understand fully the action of the instrument, and it is hoped that this article will provide a basis for a scientific appraisal of endosonics.

Ultrasonically induced cavitation in mammals

The role of cavitation in the production of biological effects in mammals is reviewed with emphasis on recent studies in the mouse neonate. The levels for hind limb paralysis from 1 MHz, continuous wave unfocused ultrasound in the neonatal mouse, within 24 h of birth, have been investigated at 1 and 16 bars ambient pressure and temperature between 10° and 37°C. Above certain intensity levels the exposure duration for paralysis of 50% of specimens exposed increases with increased ambient pressure. Since an increased ambient pressure tends to suppress cavitation, such changes suggest cavitational involvement. Results show that cavitation may be involved in the resultant paralysis above approximately 150 W/cm2 at 10°C, and above approximately 60 W/cm2 at 37°C. This temperature dependence is consistent with a cavitation mechanism. [Work supported by National Institutes of Health.]

Creep cavitation and grain boundary structure in type 304 stainless steel

Grain boundary cavitation in Type 304 stainless steel under creep loading was investigated. Scanning electron microscopy observations showed that cavitation varied significantly among different grain boundaries even when they were similarly oriented to the stress direction. Drastic changes in cavitation were also often observed across twin boundaries intersecting a grain boundary facet; this finding indicated that grain boundary structure plays an important role in cavitation. The correlation between cavity density and boundary structure was characterized by high voltage electron microscopy and Kikuchi patterns. The results were analyzed in the light of modern grain boundary models. In general, cavities were found on most random high-angle boundaries, whereas coincident site lattice (CSL) boundaries tended to resist cavitation. Of the total boundaries (excluding twins), 53% were CSL boundaries; this percentage greatly exceeds available theoretical predictions based on random grain orientation.

The Role of Cavitation in Whirl Instability in a Rotor Bearing, 2: Effect of Oil Inlet Position and Supply Pressure

Whirl orbits have been calculated for a cavitated rotor bearing in which the cavity is assumed to form at an oil inlet groove and occupy the region in which subambient pressure is predicted from the equations of motion. Variations in position of the inlet groove and in the oil supply pressure have a profound influence on the behavior of the journal, largely through the variations in cavity size and position that are produced.

The Role of Cavitation in Whirl Instability in a Rotor Bearing, 1: The π-Film Model

Dynamically loaded rotor bearings are frequently observed to perform whirling motions, in which the center of the rotor describes some sort of closed orbit. In this paper we demonstrate, by using numerical computations of whirl orbits in a simple π-film model, the role of cavitation of the lubricant in enabling fluid forces alone to drive such stable orbits for certain ranges of parameter values. For other parameter values cavitation may actually enhance the instability always associated with the effects of fluid forces in a full-film bearing.

Coolant cavitation in dynamic containment loading

After a brief introduction to the subject of cavitation in subcooled liquids and a survey of what is known regarding the key parameters in the cavitation process for water and for sodium, the basic equations of the SIMON cavitation model for use with Lagrangian containment codes and the assumptions behind them are reviewed. Some calculations using this model are then presented which show the dissipative effect of cavitation both in uncavitated liquids transmitting tension waves and in cavitated liquids transmitting pressure waves. The cavitation which develops when pressure waves are reflected at free surfaces is also examined, and some calculated results are compared with an experiment involving this phenomenon found in the literature. The role of cavitation in the containment loading process is then discussed, and examples taken from model test calculations are adduced to show that cavitation occurs at all stages of the loading process and involves a high proportion of the total liquid volume. Again by example the point is made that in certain simple circumstances a crude pressure cut-off model of cavitation is adequate but that for other major aspects of the containment loading process such as roof impact pressures and structural deformations a more refined model is necessary.

High temperature stress relief cavitation of an Al-bearing α-brass

High temperature stress relief intergranular cavitation and subsequent room temperature embrittlement of an aluminium-bearingα-brass has been studied metallographically. The behaviour of a cast susceptible to cavitation has been compared to one which does not exhibit intergranular cavitation during stress relief, and which is subsequently more ductile at room temperature. A number of micro-analytical techniques (SIMS and EDX) failed to reveal any difference in the grain boundary chemistry between a cast susceptible to intergranular cavitation and one which was not, but it is suspected that the combined action of dissolved gases (e.g. hydrogen) and trace element impurities plays a major role in cavitation. The cavities formed during stress relief were often polyhedral in shape and it is considered that this occurs by the diffusion of matter around the cavity surface to attain a lower energy surface configuration. Second phase particles were found to play only a minor role in the nucleation of cavities. Room temperature intergranular fracture surfaces of material, in which cavities had formed during stress relief, were interpreted in terms of high temperature cavity formation and coalescence combined with low temperature plastic void growth and interlinkage.

The role of cavitation in the in vitro stimulation of protein synthesis in human fibroblasts by ultrasound

The synthesis of protein by human embryonic fibroblasts in vitro was stimulated by irradiation with ultrasound at a frequency of 3 MHz, a spatial and temporal peak intensity of 0.5 W.cm −2, pulsed at a mark: space ratio of 2:8 ms for 5 min at ambient pressure. This stimulation was suppressed by the application of a positive pressure of two atmospheres during irradiation, although increasing the pressure in the absence of ultrasound had no significant effect on the rate of protein synthesis in control cells. Dilatation of the rough endoplasmic reticulum and plasma membrane changes, found in the majority of cells after treatment with ultrasound at ambient pressure, were also suppressed in cells irradiated at elevated pressure. Since it is unlikely that increasing the pressure could modify any ultrasonic effect other than cavitation, these results suggest that cavitation is involved in the mechanism of stimulation.

Role of cavitation in the process of liquid atomization in an ultrasonic fountain: Eknadiosyants, O.K. Soviet Physics-Acoustics, Vol 14, No 1 (July-September 1968) pp 80–84

Role of cavitation in the process of liquid atomization in an ultrasonic fountain: Eknadiosyants, O.K. Soviet Physics-Acoustics, Vol 14, No 1 (July-September 1968) pp 80–84

Sonochemistry: The Production of Chemical Changes with Sound Waves

An extensive survey is made of the chemical effects of ultrasonic waves. Increased understanding of the mechanism of these effects is sought through a consideration of the significance of certain experimental variables such as frequency, intensity, pressure, and temperature. Also considered is the role of cavitation.

Depolymerization by Ultrasonic Irradiation: The Role of Cavitation

Contrary to current belief, cavitation has been found responsible for the depolymerizing effect of intense ultrasonic waves. This was demonstrated by irradiating two portions of a 1 percent polystyrene solution in toluene under conditions identical except for the following. The first portion was given no special prior treatment, showed many cavitation bubbles during irradiation, and decreased in molecular weight (as measured by the intrinsic viscosity) to about one-tenth of the initial value. The second portion was given a preliminary treatment of degassing by boiling under vacuum, showed no cavitation bubbles during the irradiation, and underwent no appreciable change in molecular weight. Similar experiments with solutions of hydroxyethyl cellulose in water showed that, in this case also, cavitation is necessary for depolymerization. The opposite conclusion of earlier investigators is attributed to their inadequate method for eliminating cavitation. Oxidants known to be produced by ultrasonic waves in solutions containing dissolved oxygen or nitrogen cannot be responsible for the degradation, because substantially the same amount of depolymerization occurs even when helium is the only gas present.

Recent Progress in Supersonics

First Page

Recent Progress in Supersonics

A summary of recent contributions to several branches of acoustics which have been useful to physics and to chemistry. The theory of the propagation of sound in dispersive gases is first discussed from a standpoint which it is hoped may be intelligible to those who have no special knowledge of the subject. There follows a description of the various types of apparatus which have been devised to measure the velocity of sound and the attenuation coefficient. The direct photography of sound using Töpler's “Schlieren-methode” is stressed as promising to obviate difficulties inherent in the interferometric technique. The experimental results are then summarized with particular attention to the effects of pressure, temperature, and traces of foreign substances on the dispersive behavior of gases. The collision theory has received strong support from the majority of these measurements. Finally, the effects of intense sonic and supersonic radiation are briefly reviewed. Since most of these have been found to depend upon cavitation, the role of cavitation is examined. A ballo-electrical explanation of the phenomena is considered the most promising, although it is difficult to prove.