Cavitation Action Research Articles

Influence of preliminary cold deformation on the cavitation-corrosion resistance of 12Kh18N9T steel

However, in practice as a rule parts operating in chemically active media are subjected to cavitation action. Austenitic steels, which possess low cavitation-corrosion resistance in comparison with martensitic steels close in composition, are normally used for service in such media [4]. In connection with this it was of interest to investigate the influence of deformation martenslte formed as the result of preliminary working and also of the ~ ÷ ~ phase transformation on the corrosion resistance of austenitic stainless steels under cavitation conditions.

Dispersion and particle packing of magnetic oxide powders

Magnetic oxide powders (BaFe 12O 19, SrFe 12O 19, Fe 3O 4 and γ-Fe 2O 3) were dispersed in 36 liquid systems, and their particle packing by sedimentation investigated. Sedimentation volume mesurements showed dispersibility to be highly dependent on the liquid's polarity: nonpolar liquids such as n-hexane, benzene and cyclohexane are not suited for dense particle packing, while polar organic liquids, especially alcohols and carboxylic acids, are good dispersion media, aiding particle packing. Sediment density was doubled by agitating suspension ultrasonically, as particle agglomerates were effectively broken up by the action of ultrasonic cavitation. Application of a weak magnetic field to suspensions did not improve sediment density, but formed loose microstructures characterized by closed loops of crystallites.

The effect of temperature on mass transfer of a fluid in capillaries under the action of ultrasonic cavitation. Experiment and application

The phenomenon of an anomalous increase of mass transfer of a fluid in a capillary in an ultrasonic field (ultrasonic capillary effect) with increasing fluid temperature is studied and results are presented, as well as high-speed photomicrographic pictures of cavitation bubbles at the capillary end face. The mechanism of the effect is shown to be the inception of a resulting fluid flow into the capillary due to non-spherical collapse of cavitation bubbles at the capillary end face with the formation of cumulative microjets of fluid. The results of the use of the ultrasonic capillary effect in practice to increase the sensitivity of capillary non-destructive testing are presented.

Strain of metals exposed to cavitation

1. The mechanical characteristics determined in accordance with standard practice do not reflect the ability of materials to withstand cavitation failure. The operating stability of a material can be correlated only with a set of characteristics determined on the basis of cavitation-mechanical tests. 2. Cavitation action combined with uniaxial tensile loads reduces sharply the deformation stress and causes progressive elongation of the specimen without a marked increase in the effective stress due to the dynamic recovery phenomenon. The reduction in the deformation stress is proportional to the amount of strain and the intensity of cavitation action. 3. Ultrasound irradiation of a metal specimen subjected to uniaxial tensile loading, in contrast to cavitation action, reduces only the strain hardening coefficient.

The effect of ultrasound and mechanical stirring on the ion-exchange kinetics

The ultrasound increases the ion exchange rate in comparison with the undisturbed. Contrary to a previous report in the literature, however, its effect on ion-exchange equilibria is less than that of mechanical stirring. The effects of resin weight and the intensity of ultrasound and mechanical stirring are reported. The ultrasound effect is discussed in terms of its cavitation action on the film diffusion.

Collapse of a cavitation bubble between two solid walls

A theoretical study is made of the process of cavitation bubble collapse between two solid walls in an ideal incompressible fluid. Following the method developed and running numerical calculations on an electronic computer, the radius and rate of collapse of a cavitation bubble between two solid walls have been determined for different instants of time and angles. The presence of the second solid wall, which brings about a change in the velocity and flow pattern of the added quantity of fluid, is shown to lead to a lesser rate and a markedly different scheme of collapse of cavitation bubbles. These were observed to reduce the erosive activity of acoustic cavitation due to its lesser mechanical attack on the surface and smaller heat transfer from collapsing cavitation bubbles to the surface treated as compared to the case of only one solid wall. The results obtained, when used to select the optimal conditions for surface treatment, will allow a more effective application of ultrasonic energy in those technological processes which are associated with destructive action of acoustic cavitation resulting from high pressures and heat loads.

High-head spillway system with a countereddy energy dissipator

1. The complexity of creating reliably operating high-head spillways is due to the need to protect structural elements of tunnel linings from the action of cavitation and dynamic loads and to dissipate the excess energy of the flow directly inside the tunnel. In connection with this the problem of developing new efficient designs is especially urgent. 2. The use of swirled flows in spillway systems makes it possible to improve considerably the cavitation and dynamic conditions in the passageway and to create reliably operating high-head spillways. 3. One of the most promising spillway systems with swirling of the flow is the countereddy spillway system proposed and tested at MISI, which permits actually at any head reducing the velocity of the through-going flow to values of 15–20 m/sec, which are safe in a cavitation and dynamic respect. These properties of the countereddy spillways are confirmed by the results of laboratory investigations. 4. Preliminary technicoeconomic calculations show that the introduction of such a system into hydrotechnical construction practice opens fundamentally new ways to design high-head spillways and effects a considerable saving of capital investments.

Cavitation resistance of concrete

It is required to continue investigations of the cavitation resistance of concretes with respect to aggregates (especially porous and portland cement clinker), combined action of cavitation and frost on corrosive media, and impregnation by monomers or other variants of the combination of concrete and polymers. When updating the existing standards special attention should be devoted to strict observance of concreting technology and development of measures for assuring a suitable quality of concrete and its control.

Fatigue Maps and Wave-Shape Effects on Fatigue

Low-cycle, high-temperature fatigue failure is a complex process which can result from the combined action of time independent plasticity, intergranular cavitation and environmental effects. The dominance of one mechanism over another, and interactions between them, depends strongly on temperature, strain range, strain rate and waveshape. In particular, the effect of waveshape on the failure mechanisms is discussed in this paper. The construction of fatigue maps for some precipitation hardened copper alloys is described. Such maps define the dominant fatigue mechanism under a given set of operating conditions. Thus they are useful for defining the limitations of extrapolation techniques which are based on the operation of a single failure mechanism. Résumé La rupture en fatigue oligocyclique, à haute température, est un phénoméne complexe qui peut provenir de l'action conjointe de la plasticité (indépendante du temps), de la cavitation intergranulaire et des effets de l'environnement. La prédominance d'un de ces mécanismes et leur interactions sont grandement influencées par la température, la forme du cycle, le niveau et le taux de déformation. Cet article insiste particulièrement sur l'influence de la forme du cycle sur les mécanismes de fissuration. On décrit comment sont mis au point des diagrammes de fatigue pour des alliages de cuivre durcis par précipitation. Suivant les conditions d'essais, ces diagrammes sont utilisés à déterminer le mécanisme dominant en fatigue; ils sont donc bien pratiques pour fixer les limites des techniques d'extrapolation, basés sur un seul mécanisme opérant.

An investigation of the fine structure of metals deformed under cavitation action in water and liquid nitrogen

An investigation of the fine structure of metals deformed under cavitation action in water and liquid nitrogen

Platelet Aggregation Induced in Vitro by Therapeutic Ultrasound

SummaryPlatelets were found to aggregate spontaneously when exposed to ultrasound generated by a commercial therapeutic device. At a given frequency, aggregation was found to be a dose-related phenomenon, increasing intensities of ultrasound inducing more extensive and more rapid aggregation. At any single intensity, the extent aggregation was increased as the frequency of the applied ultrasound was decreased (from 3.0 to 0.75 MHz).Ultrasound-induced platelet aggregation was found to be related to overall platelet sensitivity to adenosine diphosphate. More sensitive platelets were found to aggregate spontaneously at lower intensities of sound, and also the maximum extent of aggregation was found to be greater. Examination of ultrasound-induced platelet aggregates by electron microscopy demonstrated that the platelets had undergone the release reaction.The observation that haemoglobin was released from erythrocytes in whole blood irradiated under identical physical conditions suggests that the platelets are being distrupted by ultrasonic cavitation (violent gas/bubble oscillation).It is postulated that overall platelet aggregation is the result of two distinct effects. Firstly, the direct action of ultrasonic cavitation disrupts a small proportion of the platelet population, resulting in the liberation of active substances. These substances produce aggregation, both directly and indirectly by inducing the physiological release reaction in adjacent undamaged platelets.

Present trends in protection of hydraulic turbines against cavitation pitting

1. The most important a pproach for increasing the wear resistance of hydraulic turbines against cavitation is the development of hydrodynamic means for controlling the cavitation and reducing its pitting capacity. Of great significance is the development of cavitation-resistant materials and coatings and of techniques for applying them. The electrochemical means for protection against cavitation have not yet been sufficiently developed for extensive use. It is convenient to organize laboratory investigations on cathodic protection and methodical testing of this type of protection in one or two small turbines. 2. An important method of preventing cavitation pitting is the proper selection of the operating regimens. At the present time, methods have been worked out for predicting the intensity of cavitation action under different operating regimens of the turbines, on the basis of analytical data about the pressure distribution. The relative pitting hazard can be tentatively evaluated from the intensity of recorded acoustic radiations.

噴流による固体壁面の壊食機構 (キャビテーション壊食) について

The action of a stream flowing from a nozzle 2mm. in diameter at the velocity of 100-300m/s in eroding solids is investigated. The effect on erosion of the distance from the nozzle and the angle of incidence of the stream is studied. Experiments show that the stream produces the most destruction when the streamis divided. The results can serve as a confirmation of the theory of the destructive action of cavitation, based on the multiple renewal of direct blows delivered to the surface of the solids by the liquid.

Improving the flow of liquid from a nozzle by inserting an air tube

1. The wear of hydromonitor nozzles is due to the cavitation action of the liquid stream. 2. The cause of this cavitation is the presence of a vacuum near the mouth of the nozzle. 3. The wear can be effectively suppressed by eliminating the vacuum. 4. One method of eliminating the vacuum in the nozzle is to introduce an air tube, as used in the PG pulsed hydromonitor for creating pulsations in the jet.

On the Destructive Action of Cavitation

On the Destructive Action of Cavitation