Cavitation Action Research Articles

Interrelation between the cavitation resistance and microhardness of metals

Under the action of cavitation induced by an ultrasonic vibrator in tap water, we determine experimentally the level of fracture of transition metals that belong to Groups IV—VI of the periodic table. It is shown that the cavitation resistance of the metals is determined by the microhardness with an error of ±10%. For the preliminary assessment of the cavitation resistance, we can use the relation Z h = 2.42 ∙ 10-2 H μ 3 , where the microhardness is determined in GPa.

Physical model of energy activation of anode microarc oxidation

A physical-mathematical model of energy intensification of the microplasma-spark treatment of a material in a liquid by passing ultrasonic waves through it is proposed. The conditions of ultrasound action and its parameters as well as the characteristics of the liquid medium carrying an electric pulse were determined for optimization of the cavitation and energy action on the modification and hardening of "venting" materials in the process of their anode microarc oxidation. An analysis of the results of simulation of the physical effects arising in the process of anode microarc oxidation of materials under the indicated conditions has shown that this process can be controlled for the purpose of obtaining definite-thickness and quality coatings by searching for an external ultrasound action with a certain amplitude and frequency and an electrolyte possessing special characteristics determined by its density, viscosity, and the presence of particles with a definite degree of dispersion.

Cavitation technologies for dispergation and homogenization

The results of tests carried out in industrial conditions are presented. They allow one to propose cavitation technologies of dispergation and homogenization for fabricating emulsions and suspensions under the action of ultrasonic, hydrodynamic, and hydroacoustic cavitation. The dispergation regimes were found for materials with various physicochemical properties, including viscous media (natural juices with pulp) and materials with a lamella structure (bentonite). Cavitation effects intensify dispergation processes and allow one to produce materials with submicronic dimension of the particles; this considerably increases the sedimentation period of the suspensions.

The ultreo: A novel toothbrush that combines sonic and ultrasound physics.

Efficacious, daily oral health care represents an important part of maintaining the overall health of individuals. Here we sought to develop and demonstrate the usefulness of a new power toothbrush, one that incorporated both sonic processes (in the form of rapid bristle motion that directly removes plaque as well as generates bubbles) and ultrasound (sourced from the brush head, that activated the bubbles). We adapted a set of existing power toothbrushes to incorporate an ultrasound source with sufficient controls to explore the effects of different ultrasound parameters on plaque removal in vitro and in vivo. The combination of sonic and ultrasound physics removed plaque in vitro in a synergistic manner, likely through the action of cavitation. In vivo, the Ultreo toothbrush—a commercial version of this brush—removed comparable amounts of plaque to another commercial brush in half the time, and removed more plaque than manual toothbrushes. A combination of sonic bristle motion and ultrasound-facilitated cavitation appears to produce superior plaque removal compared to existing, sonic only, or manual tooth brushes.

STONE FRAGMENTATION AND CLEARANCE DURING SHOCKWAVE LITHOTRIPSY USING THE APPLIED® MEDICAL URETERAL ACCESS SHEATH

Extracorporeal shock waves have recently been introduced to treat pseudarthrosis and aseptic bone necrosis. Only little information exists up to now about the morphological effects of shock waves on normal bone. To study both their acute effect on bone and their long-term effect on its remodelling, 1500 shock waves generated with a Dornier XL1 experimental electrohydraulic lithotripter were applied at 27.5 kV to 19 rabbits divided into five groups. Changes were evaluated after 6, 11, 41, 59 and 85 days. The discharges were focused to the right femur 1 cm above the knee joint. Bone remodelling was assessed in four groups by four-colour fluorescent labelling with labels administered sequentially over 8-day periods during the first month after shock-wave application. Radiographs were taken at dissection to detect fractures. As a result, shock waves were found to induce periosteal detachment with subperiosteal haemorrhages and to press marrow contents out of the medullary cavity. In the medullary cavity, diffuse haemorrhages, haematomas and foci of fractured and displaced bony trabeculae were found. The bone cortex and the knee joint were normal. Radiographs showed lucencies in the marrow but no fractures. During the weeks following shock-wave application, there was intense apposition of new cortical bone resulting in considerable cortical thickening while trabecular remodelling in the medullary cavity was only minor. The displacement of bony trabeculae and marrow contents point to the action of cavitation as the major mechanism of shockwave damage to bone.

Cavitation damage of the medium carbon steel: Implementation of image analysis

Cavitation damage of the medium carbon steel was performed using the modified vibratory cavitation test set up. Erosion rates were measured by analytical method. The morphology of damage under cavitation action was determined by optical microscopy techniques. Image analysis was used for determination change of the ratio of ferritic phase in the heat treated medium carbon steel during cavitation action. Implementation of image analysis was done by Image Pro Plus Program.

Force acting on a cylinder under ultrasonically induced cavitation

To elucidate mechanisms of cavitation action on a surface with microcapillary discontinuity and refine the model of the sonocapillary effect, the force acting on a cylinder is correlated with the height of a liquid in the capillary under cavitation, both quantities being measured at the same point of the ultrasonic field. It is found that the force acting on the cylinder is directed toward a cavitation cluster stabilized at the end face of the cylinder. This force can be enhanced with another cylinder placed on the side of the cluster coaxially with the first one. The dynamics of the cavitation cluster depending on the cylinder spacing is investigated in the case when one of the cylinders is on a pendulum suspension. The conditions for self-sustained oscillations of the pendulum are found. The dependence of the attracting force between the cylinders on the ultrasonic frequency and cylinder spacing is derived. The end-face-averaged pressure exerted on a cylinder of diameter 1.2 mm may reach 0.16 kPa, and the intracapillary pressure attains 0.89 kPa. Thus, the sonocapillary effect may be explained, at least partially, by a counterpressure arising from cluster-capillary interaction. This effect can be used in designing cavitation sensors and ultrasonic sources.

Stone orientation affects the mechanism of failure in artificial kidney stones subject to shock waves

Micro computed tomography (CT) imaging was used to follow the progressive development of cracks in artificial kidney stones. The artificial stones were made from U30 cement with a cylindrical shape (6.5 mm diameter and 8.5 mm long). The stones were held within a polypropylene vial in one of three orientations: vertical, horizontal, and angled at 45 deg. The stones were treated with an electromagnetic lithotripter and the initiation and growth of cracks was observed using microCT. The images show that the orientation of the stones with respect to the shock changes the dominant mechanism for fragmentation. Vertical stones developed a spall-like crack near the distal surface, which propagated from the surface to the interior of the stone. Initiation of a secondary spall-like crack was observed proximal to the first crack. Little surface damage was observed. Horizontal stones presented pitting in the proximal surface and erosion in lateral faces, indicating the action of cavitation. Angled stones presented both spall-like fracture in either the leading or the distal corners and surface damage (pitting) in the proximal surface. Experiments are being performed to follow the development of cracks in human kidney stones. [Work supported by the Whitaker Foundation.]

Erosion of Vacuum-Arc Ti–N Coatings

We studied the fracture of vacuum-arc Ti–N coatings, produced under a nitrogen pressure (PTiN) from 1 to 103 mPa, after their bombardment with polyenergetic deuterium ions and the action of cavitation in tap water on them without ion irradiation. We showed that, in the case of action of cavitation on nonirradiated specimens of the coatings, their erosion rate can be evaluated from the relation Vc = C/(W0.75H0.5). It was established that, after ion bombardment, the erosion rate under conditions of cavitation decreases by a factor of 1.5 for coatings where PTiN > 100 mPa and increases by more than 30 times for PTiN < 20 mPa as compared with nonirradiated specimens. The results obtained were analyzed using the phase diagram of the titanium-nitrogen system.

Beitrag zum Löten von Magnesiumwerkstoffen / A Contribution to Soldering of Magnesium Materials

The progress made in developing magnesium materials and the currently increased interest in those materials require appropriate technologies in joining such materials. In many cases soldering is the best appropriated joining technique, particularly if there are many joining points an access to which is difficult. Soldering magnesium alloys has hardly been used hitherto because there are considerable problems of corrosion and erosion in employing fluxes. For a long time, there has been a need for a soldering technology which makes it possible to solder high alloyed magnesium alloys by using low-melting solders while not worsening their corrosion properties additionally as this technology avoids fluxes. A technology for soldering magnesium materials using no fluxes was developed. The destruction of the oxidic surface layer comes about by the action of cavitation and mechanical activation of the joining surfaces in an ultrasonically activated, liquid solder.

Ultrasound decontamination of minimally processed fruits and vegetables

The effectiveness of power ultrasound for the microbial decontamination of minimally processed fruits and vegetables was studied. Reductions in Salmonella typhimurium attached to iceberg lettuce obtained by cleaning with water, chlorinated water, ultrasound with water and ultrasound with chlorinated water were 0.7, 1.7, 1.5 and 2.7 logs, respectively, for small‐scale (2 L) trials. The cleaning action of cavitation appears to remove cells attached to the surface of fresh produce, rendering the pathogens more susceptible to the sanitizer. For large‐scale (40 L) trials, the addition of chlorine to water in the tank gave a systematic difference in Escherichia coli decontamination efficiency. However, the frequency of ultrasound treatment (25, 32–40, 62–70 kHz) had no significant effect on decontamination efficiency (P &gt; 0.69). With the potentially high capital expenditure together with the expensive process of optimization and water treatment, it is unlikely that the fresh produce industry would be willing to take up this technology. Furthermore, the additional one log reduction achieved by applying ultrasound to a chlorinated water wash does not completely eliminate the risk of pathogens on fresh produce.

Determination of the Relaxation Time of Physico-Chemical Characteristics of Water After Cavitation Treatment

The results of hydrodynamic treatment of water in the supercavitation mode are presented. Changes in the physicochemical properties of water (electrical conductivity, pH, oxidation-reduction potential (ORP), oxygen content (OCP), etc.) were revealed, the rational duration of cavitation treatment of water was established, and data on the relaxation of these properties were obtained. At the same time, there is an increase in temperature, pH and electrical conductivity, a decrease in ORP and CRC. The time range with the most intense changes in pH and ORP is 30–90 s. The rate of pH and ORP change in the range of 30–90 s is three and two times higher, respectively, than in the range of 90–300 s. These results correlate fairly well with the results of studies of the effect of ultrasound on water. It was found that the maximum pH value is reached under cavitation action for 180 s. The minimum value of ORP takes at 300 s of cavitation treatment, but remains in the area of positive values. It is shown that during the relaxation time, activated water after treatment for 200 min under the used modes of hydrodynamic cavitation treatment does not return to its original state in all measured parameters

Cavitation erosion of copper and copper-based alloys

Cavitation erosion studies of five multiphase copper-based alloys for a screw propeller application and of three α-solution alloys of comparative purpose have been carried out to determine the resistance of the alloys to cavitation erosion and to understand the influence of the microstructure and/or composition of the alloys on the morphology of erosion damage. The experiments were conducted using a vibratory system. Erosion rates were measured, and the mechanism of damage under cavitation action was studied. No correlation between the cavitation erosion resistance (CER) and the mechanical properties of the alloys has been found. However, a good correlation between the resistance and work-hardenability, defined by means of stacking-fault energy (SFE), being a chemistry-dependent property, has been established for the α-solution alloys. A better CER can be expected for a lower SFE and higher work-hardenability. The resistance of the multiphase alloys in terms of chemical composition and mode of damage was discussed. An advantageous influence of nickel and aluminum and a low effectiveness of zinc on cavitation resistance have been outlined.

Induction of base damage in dna solutions by ultrasonic cavitation

Ultrasound can damage macromolecules by the mechanical (shearing) and sonochemical (free radical generating) action of ultrasonic cavitation. Attributing macromolecular damage to either direct mechanical stress or to indirect mechanisms involving free radicals or other sonochemicals is a challenging problem. DNA damage induced by ultrasound was evaluated by measuring the formation of purine and pyrimidine products using combined gas chromatography-mass spectrometry with selected ion monitoring. Samples of DNA were prepared in 10 mmol dm −3 phosphate buffered saline (pH 7.4) and saturated with a mixture of argon:oxygen (3:1). Continuous 2.17 MHz ultrasound exposures at 0.82 mPa spatial peak negative pressure amplitude were performed in a 60 rpm rotating tube exposure system. Hydrogen peroxide yields were measured after each exposure to quantify the cavitation activity and ranged up to 350 μmol dm −3 for 1-h exposures. Purine and pyrimidine products identified were those typically observed following exposure of DNA to hydroxyl radical-generating systems, such as ionizing radiation, hypoxanthine/xanthine oxidase, or hydrogen peroxide in the presence of transition metal ions. The yields of these products were directly correlated with cavitation activity as measured by residual hydrogen peroxide concentrations. The yields of DNA products increased in the following order: thymine glycol∼cytosine glycol>8-oxoAde>:FAPyAde-5-HMU∼5,6-diOHCyt>FAPyGua. Unexpectedly, 8-oxoguanine did not exhibit a dose-dependent increase above background levels, and this observation is inconsistent with processes involving metal ion-dependent formation of hydroxyl radicals from hydrogen peroxide. In addition, the product yields were far too large to result from the residual hydrogen peroxide. Thus, ultrasonic cavitation appears to have a mode of action distinct from either ionizing radiation or formation of hydroxyl radicals via Fenton-like reaction with transition metals.

Biological effects of shock waves: In vivo effect of high energy pulses on rabbit bone

Extracorporeal shock waves have recently been introduced to treat pseudarthrosis and aseptic bone necrosis. Only little information exists up to now about the morphological effects of shock waves on normal bone. To study both their acute effect on bone and their long-term effect on its remodelling, 1500 shock waves generated with a Dornier XL1 experimental electrohydraulic lithotripter were applied at 27.5 kV to 19 rabbits divided into five groups. Changes were evaluated after 6, 11, 41, 59 and 85 days. The discharges were focused to the right femur 1 cm above the knee joint. Bone remodelling was assessed in four groups by four-colour fluorescent labelling with labels administered sequentially over 8-day periods during the first month after shock-wave application. Radiographs were taken at dissection to detect fractures. As a result, shock waves were found to induce periosteal detachment with subperiosteal haemorrhages and to press marrow contents out of the medullary cavity. In the medullary cavity, diffuse haemorrhages, haematomas and foci of fractured and displaced bony trabeculae were found. The bone cortex and the knee joint were normal. Radiographs showed lucencies in the marrow but no fractures. During the weeks following shock-wave application, there was intense apposition of new cortical bone resulting in considerable cortical thickening while trabecular remodelling in the medullary cavity was only minor. The displacement of bony trabeculae and marrow contents point to the action of cavitation as the major mechanism of shockwave damage to bone.

Cavitation in swirled flows

1. With an increase of the flow velocity v from 7.58 to 14.67 m/sec and change of k/kcr in the interval of the most erosion-active values from 0.75 to 0.39, Eph increases proportionally to v5, although Ef increases proportionally to v3. This indicates that in the presence of general erosion activity of the cavitation regime of the flow, a small erosion action on the wall is observed in swirled flows. 2. The cavitation jet in swirled flows is directed at an angle toward the axis of the conduit as a consequence of the emergence of bubbles in the field of centrifugal forces. This angle and the rate of emergence vemer increase with increase of the swirl angle α and flow velocity v. 3. The milder erosion action of cavitation in a swirled flow compared with an axial flow for the same cavitation regimes is explained by the large values of pressure at the wall (due to centrifugal forces), emergence of bubbles, and direction of the cavitation jet toward the wall.

金属の電析におよぼすジェット流の理論的考察

The effects of ultrasonic waves on electrolysis consist mainly of cavitation action. The collapse of cavitation bubbles in liquid generate collapse pressure, jet flow and impulse pressure due to the jet flow. First, the collapsing motion of a single bubble near a electrode surface was modeled, and equations of motion for a spherical gas bubble were obtained. Next, the properties of deposits were studied on the basis of the equations of motion. The jet flow speed and liquid pressure due to water hammer were calculated using equations (33) and (34) in liquid. For example, when the jet flow speed was 120m·s-1, the water pressure was about 2000atm. The mass transfer on the electrode was a turbulent diffusion. The jet flow and pressure affected the entire mechanism of electrodeposition: the rate of deposition, current efficiency, hardness, roughness and particle size of deposits were affected.

Arrhythmogenic action of acoustic cavitation on the isolated rat heart perfused with physiological saline

Arrhythmogenic action of acoustic cavitation on the isolated rat heart perfused with physiological saline

Reduction of cavitation action on a surface being treated by diminishing the gap

The nature of the collapse of cavitation bubbles is examined for different gaps between the specimen and the ultrasonic emitter. A method is proposed for reducing the cavitation action on the surface being treated by diminishing the gap to values on the order of the maximal diameter of the cavitation bubbles. A formula is found to compute the gap domain with lowered cavitation action. The results obtained can be utilized in the realization of ultrasonic technological processes associated with the action on cavitationally unstable materials.

The role of sand particles on the rapid destruction of the cavitation zone of hydraulic turbines

Metal surfaces in the cavitation zone of hydraulic turbines working in sandy water are damaged rapidly. The damage is much more severe than that caused either by sand erosion or by cavitation alone. This paper presents an analysis of a worn surface of 18Cr-8Ni steel tested in a Venturi device at a hydroelectric power station in the flood season. Two types of damage were found. The first was a smooth erosion in the area of regular fluid flow. The second was in the regions where cavitation occurred. In the latter regions, the sand particles gain high velocities under the action of cavitation, impinge upon the metal surface and cause severe surface deformation and rapid damage. Embedded sand particles, cavities, cracks, cutting scars and fatigue patterns were found on the sponge-like worn surface.