Stage Of Cavitation Research Articles

A comparison of the cavitation erosion resistance of TiNi alloys, SUS304 stainless steel and Ni-based self-fluxing alloy

Cavitation erosion of TiNi shape memory alloys, SUS304 stainless steel (SS) and Ni-based self-fluxing alloys has been investigated in freshwater and 3.5 wt.% NaCl solution according to the ASTM G32-85 standard method. After 300 min of cavitation erosion, the cumulative weight loss of SUS304 SS is 45 times, whereas that of Ni-based self-fluxing alloy is 15 times the value of TiNi alloys. TiNi alloys and SUS304 SS exhibit a working-hardening behavior in the early cavitation stage, and thereafter maintain constant hardness during further cavitation. However, the Ni-based self-fluxing alloy exhibits no hardening phenomenon during cavitation test. The thermoelastic martensitic transformations of TiNi alloys have important effects on their erosion characteristics. The variants accommodation, pseudoelasticity of SIM and high work-hardening rate can improve the erosion resistance of TiNi alloys. Cavitation erosion of all these alloys in freshwater is similar to that in 3.5 wt.% NaCl solution under the same testing conditions.

Ｈｅ ＩＩ流れにおけるキャビテーションの可視化および圧力変動

The cavitation phenomenon in He II flow through a two-dimensional Venturi channel was investigated by visualization and pressure measurement. Liquid helium flow was made by shrinkage of bellows pump, and the cavitation was induced in the flow at the throat of the channel. The overview of cavitation can be observed through the optical windows of the cryostat, and was recorded by a high-speed video camera and a still camera. The pressure loss due to the flow through the channel was measured by a differential pressure transducer. By analyzing the pressure loss data, the static pressure at the throat of the channel could be estimated. Through this experiment, it was found that cavitation in He II flow has some unique characteristics different from ordinary fluids. Once cavitation is induced in an He II flow, it jumps suddenly to fully developed scale without the weak cavitation stage seen in other fluids.

Observation of Cavitation Inception in Hydraulic Oil Flow.

It has been known that the traditional "nucleus" theory for cavitation is incompatible with some physically and experimentally recognized facts. In order to re-examine the issue cavitation in a hydraulic oil flow through a long two-dimensional acrylic constriction has been observed by strobos-copic photography with a microscope, laser beam transmission and pressure and noise measurements. A revelation was that at the very incipient stage of cavitation, a microscopic cavity suddenly emerges and attaches on the inlet edge. Luminescence was also observed in the cavitation together with electrostatic charge. All the findings, which cannot be consistently explained by the nucleus theory, lead to the following speculation ; at the separation point a tensile force rips off a liquid particle from the wall, leaving behind a tiny vacuum vecancy, which forms the incipient cavity on the edge. This rip off action also results in electrostatic charges, which cause light emission when discharged in the vacuum.

Flow Visualization of Cavitation in a Cylindrical Choke.

This paper deals with an experimental study on the flow visualization of cavitation for steady and unsteady flows in cylindrical chokes of oil hydraulics. Experiments for the unsteady flow are carried out under a condition in which the inlet pressure p1 in the cylindrical choke takes a trapezoided form with time, while keeping the outlet pressure p2 constant. The behavior of the cavitation bubbles is clarified with an ultrahigh-speed camera under two geometric parameters: the diameter and the chamfered length of the choke. Also, a method for suppressing the occurrence of cavitation is studied. It becomes clear that a bubble which appears in the earliest stage of cavitation "grows, collapses, disappears and reappears repeatedly" at intervals of about 1.0x10-4 seconds.

DNA methylation in early development.

Several lines of evidence strongly suggest that DNA methylation is involved in embryo development. Perhaps the most direct evidence comes from experiments with methyltransferase deficient mice. Embryos that express low levels of the maintenance methyltransferase do not develop to term and die at the 5 to 20 somite stage corresponding to the level of the enzyme. In the mouse, dramatic methylation changes have been observed during the early steps of embryo development. Most genes are subject to a process of active demethylation starting promptly after fertilization. Except for a small number of methylated CpG sites in imprinted genes the vast majority of the sites are unmethylated by the stage of cavitation (16 cell). Such genome-wide demethylation may signify an erasure of epigenetic information originating in the highly differentiated gametes. This erasure may be essential for the establishment of a pluripotent state, before specific cell lineages can be determined. The process of laying down a new developmental program involves, initially, global de novo methylation at the stage of pregastrulation followed by gene specific demethylations associated with the onset of activity of these genes. CpG islands characteristic of housekeeping genes, appear to be protected from the global de novo methylation. An exception to this rule is the hypermethylation of CpG islands in X-linked housekeeping genes on the inactive X chromosome and of specific differentially methylated CpG sites in imprinted genes. Primordial germ cells escape the global de novo methylation which takes place at the pregastrula stage and undergo a very similar de novo methylation process in the differentiated gonads (15.5-18.5 days post coitum), forming the methylation patterns which are specific to the gametes. Specific demethylations then form a terminal methylation pattern which is then clonaly inherited in the soma and erased after fertilization.

Expression of β-amyloid precursor protein in axons of periventricular leukomalacia brains

Human β-amyloid precursor protein immunoreactivity was demonstrated in axonal swellings (spheroids) around periventricular leukomalacia (PVL) of neonates. Immunoreactive axons were found at the early, but not late stage of PVL. β-Amyloid precursor protein immunoreactivity was homogeneous in damaged axons at the early stage of PVL manifesting microglial activation, concentrated at the center of axonal swellings at the subsequent stage manifesting astrogliosis, and undetectable at the terminal stage of cavitation or neovasculation. Immunostaining for β-amyloid precursor protein was useful in localizing PVL lesions at their early stages.

バタフライ弁の流体力学的特性

There are several stages of Cavitation phenomena in the flow around butterfly valves. The cavitation stage such as cavitation inception, supercavitation inception, cavitation damage inception, choking (or flashing) cavitation occurs for the various valve opening angles. In this paper, these cavitation stages were theoretically predicted for valve loss coefficient. The cavitation prediction was performed by applying the free streamline theory, where the relation between the loss coefficient and the critical cavitation factor were formulated. As for the experiment, the cavitation inception and critical supercavition were obtained from the vibration intensity rising and the noise level rising, and the flashing cavitation was observed by means of flow visuarization. The theoretical predicted characteristic curves and these experimental results were compared, and agreed very well with each other.

Opening of the mouse zona pellucida by laser without a micromanipulator

A contact-free laser system is described for ablation of the embryonic mouse zona pellucida using a pulsed excimer 308 nm laser. Effects on further embryonic development were evaluated. Zonae of 8- to 16-cell mouse embryos were either lased (n = 189), zona-drilled with acidified Tyrode's solution (n = 183) or left zona-intact (n = 188). Blastocyst formation (99-100%) was similar in the three groups. Hatching occurred earlier in lased embryos compared to those of the control group. These blastocysts hatched through the laser ablated area. Significantly more embryos were hatching on day 4 in the conventionally drilled group when compared to the laser treated group (50% versus 24% respectively). On day 7 of development, significantly (P < 0.05) more embryos conventionally zona-drilled (37%) were intact than those which were previously laser treated (10%). Abnormal development was also noted in a small group of embryos which were lased just on the outside of the zona in comparison to 1/3 of an embryonic width away from the zona. The current results suggest that apparently precise zona laser ablation with an excimer laser at 308 nm may have potential adverse effects which may only be manifested after a prolonged period of culture past the cavitation stage. However, implantation rates of morphologically normal laser abalated embryos were not impaired when compared to control embryos.

Improved quality of human embryos when co-cultured with human ampullary cells.

Cultured human, ampullary, epithelial cells obtained from fertile women undergoing hysterectomy were evaluated for the support of human embryonic cleavage and growth in vitro. Twelve patients provided 23 embryos for co-culture with subcultured ampullary cells grown in T6 + 15% patient's serum and 18 embryos for growth in T6 + 15% patient's serum alone (controls). Of embryos co-cultured with ampullary cells, 78% cleaved to the compacted embryo stage and 69% cavitated as compared with 50 and 33% respectively for controls (P less than 0.01). Only 30% of co-cultured embryos reached the expanded blastocyst and 26% underwent hatching as compared with 28% for both stages in controls. At the 2 - 4- and 6 - 8-cell stages, 91 and 87% of co-cultured embryos showed an absence or slight fragmentation as compared with 72 and 61% respectively for embryos grown in medium alone (P less than 0.01). None of the co-cultured embryos showed unequal-sized blastomeres while 22% of controls showed unequal cleavage. Embryos grown with ampullary cells cleaved slightly faster than controls. Scanning electron micrographs showed that ampullary cells collected from co-cultures were all of the secretory type with several microvilli and apical protrusions. It is clear that subcultured human ampullary cells support human embryonic cleavage and yield a reasonable number of good quality embryos up to the cavitation stage. Development past the expanded blastocyst and hatching stages seems to involve another critical phase with its own specific requirements.

Structural factors governing steel resistance during operation in corrosive media under cavitation conditions

Maraging steels treated for maximum hardness or overaging exhibit high cavitation-corrosion resistance in acid solutions as a result high strength and resistance to microcrack initiation and propagation, whose develoment is typical for the stage of intense cavitation. In view of this, in order to improve the endurance of components operating under cavitation conditions in corrosive media, and to reduced equipment stoppages for repair, it is recommended that high alloy austenitic corrosion-resistant steels are substituted by maraging steels.

Similarity problem of inceptive cavitation

In the preceding articledai][1], the relation between thermodynamics condition and inceptive cavitation stage has been discussed. In this paper, we try to introduce the volume function of inceptive cavitation bubbles, z0(r), instead of the energy equation used in the reference ai][1], for discussing cavitation similarity problem in similar flow systems. Under this condition, theoretical result shows that the inception cavitation number Ki increases with a rise of geometry linear scale. In other words, if two flow systems are kept with similar pattern and liquid, it is impossible to satisfy the cavitation similarity. This conclusion accords with practice.

Grain boundary cavitation in internally oxidized copper

A study has been carried out of the influence of the nature and distribution of grain boundary particles on the nucleation of cavities. Dilute alloys of copper with silicon have been internally oxidized to produce a material containing SiO 2 particles. By using a variety of compositions and oxidizing temperatures a large range was obtained in the size and spacing of the particles. Specimens made from the oxidized material were subjected either to time-independent (creep) or to cyclic (fatigue) loading at elevated temperatures. Quantitative data on the early growth stage of cavitation were obtained from shadowed two-stage replicas of specimens subjected to high temperature deformation. It was found that voids invariably nucleate at the intersection of an oxide particle with the grain boundary. Over the entire range of deformation conditions used, either voids of a spherical cap shape or coalesced voids which individually had been of a spherical cap shape were observed. No evidence of crack-like growth was found. Voids do not appear to form on every grain boundary particle at the onset of deformation. For cyclic loading, voids tend to form on boundaries oriented for a large component of shear stress. The extent of cavitation is inversely proportional to the area fraction of the boundary covered by the oxides, suggesting that grain boundary sliding plays an important role in the nucleation of fatigue-induced voids. Most creep cavities are found on boundaries lying approximately transverse to the stress axis. The extent of cavitation depends strongly on the average edge-to-edge spacing between oxides but not on the area fraction of grain boundary oxides. These observations are consistent with a creep cavity nucleation mechanism assisted by dislocation pile-ups. Changing the shape of the grain boundary particles from ellipsoidal to spherical (by recrystallizing oxidized single crystals) or changing the interfacial energy (by alloying copper with titanium rather than silicon) alters the extent of cavitation in a manner consistent with theoretical predictions.

Motion of a liquid-gas bubble mixture in the incipient cavitation stage

This article is concerned with the nonsteady motion of a mixture of an ideal incompressible liquid with gas bubbles in the incipient stage of cavitation. Solutions are obtained in the first and second approximations. The solutions are applied to pipe flow situations.

Inception of Cavitation From a Solid Surface

This study of cavitation inception from a solid surface includes the presentation of an empirical model for the nuclei, a completely new design for experimental test equipment, a rigorous analysis of liquid conditions within the test section, and quantitative test data. The results prove that it is possible to reduce the effective size of cavitation nuclei, thereby making the interface more resistant to cavitation. The empirical model for cavitation nuclei provides the mechanism for bubble formation from gas-filled, submicroscopic crevices in a solid surface. The size of these nuclei may be reduced by forcing the liquid into these crevices. If the liquid-solid interface is hydrophilic, the pressure treatment is permanent, but the liquid will pull out of a hydrophobic interface thus providing only a temporary reduction of nuclei dimensions. The newly designed experimental equipment for cavitation inception studies has been demonstrated to produce cavitation under controlled conditions. The test section resembles a 180-deg journal bearing constructed in three slices. The middle slice is slid away from the journal to produce a diverging wedge which induces a tensile stress in the liquid. The inception stage of cavitation is detected by an acoustical probe. The temperature and pressure distributions in the thin film are calculated numerically by successively solving the energy and generalized Reynolds equations. A strongly implicit iteration algorithm is employed to solve the large set of simultaneous algebraic equations resulting from placing the nonlinear elliptic partial differential equations in finite difference form. Experimental data from test runs with petroleum oil, glycerin, and a glycerin-soap mixture showed that stress required for inception of cavitation could be determined with a repeatability of ±1.4 × 104 Pa (±2 psi). A linear relationship was experimentally determined to exist between the magnitude of pressure forcing oil into the crevices of a steel surface and a capacity of the oil-steel interface to withstand a tensile stress.

The prevalence of dental caries, plaque and gingivitis in 3-year-old Danish children.

abstract – The purpose of the present study was to obtain an estimate of the prevalence of dental diseases in 3‐year‐old Danish children in areas with various fluoride concentrations in the drinking water. 449 children from one high‐fluoride area (1.1–1.5 ppm F) and three low‐fluoride areas (0.05–0.50 ppm F) were examined. The recording procedure allowed differentiation between initial carious lesions (“white spot”) and carious lesions with clinically detectable cavitation. Mean deft and defs were significantly lower in the high‐fluoride area than in any of the low‐fluoride areas when initial carious lesions (“white spot” were included in the calculations of the results. When only carious lesions reaching the stage of cavitation were included in the calculations, mean deft and defs were identical in the high‐fluoride area and two of the low‐fluoride areas. The third low‐fluoride area had significantly higher mean deft and defs than the high‐fluoride area. Differences in mean deft and defs were related to a low prevalence of carious lesions on smooth surfaces in the high‐fluoride area and a high prevalence of occlusal lesions in one of the low‐fluoride areas. The prevalence of plaque and gingivitis was higher than that reported in earlier studies. Approximately 25% of all gingival units showed bleeding after slight probing. No statistically significant differences in plaque accumulation or in the occurrence and severity of gingivitis were observed between the four groups of children. No cases of endemic dental fluorosis were found.

Erosion Due to Incipient Cavitation

Van Iterson's experiments show that cavitation erosion is produced by the collapse of minute air bubbles in water in a state of air supersaturation. This is contrary to the usual conception that cavitation erosion is due to the collapse of vapour bubbles. The author gives results of experiments which indicate that the bubbles which form and collapse at the stage of incipient cavitation in aerated water are air bubbles in a supersaturated state. The experiments also show that vapour bubbles which collapse in de-aerated water are in thermal equilibrium. It is shown that the collapse of bubbles in thermal equilibrium cannot cause erosion because the vapour pressure inside and the hydrostatic pressure surrounding the bubbles are balanced during collapse. The energy producing cavitation erosion is the free surface energy liberated by the collapse of the air bubbles. The final collapse velocity is the velocity of sound in water and the magnitude of the blow produced is of the order of 120 tons per sq. in. or more. The effect of these views on the interpretation of the model tests in cavitation tunnels and on the cavitation number is discussed.