Cavitation Imaging Research Articles

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF CAVITATING FLOW IN OIL HYDRAULIC BALL VALVE

The three-dimensional cavitating flow issuing from the orifice of a ball valve was numerically investigated using the combination of RNG k-e turbulence model and multiphase flow model. The cavitation region was predicted for axisymmetric and non-axisymmetric case when the ball moves to one side. Flow visualization experiment was conducted to capture cavitation images near the orifice of the ball valve using high-speed video camera. The predicted and observed cavitation regions agree well. Furthermore, the noise spectrums of the ball valve in cavitation and non-cavitation cases were measured. The results show that the cavitation around the orifice occurs periodically with a very high frequency of 2500 Hz. The predicted cavitation region for axisymmetric and non-axisymmetric case was compared with experimentally visualized cavitation image. It was expected that the ball vibrates in the lateral direction and cavitation occurs periodically.

SWL stone fragmentation in vitro is improved by slowing the SW delivery rate

Fast shock wave (SW) rates in lithotripsy (SWL) generate enhanced cavitation that could promote stone fragmentation. We tested the idea that SWL at the high end of clinical SW rate (2 Hz) acts to improve stone comminution. Model stones (Ultracal-30 cement) were exposed to SWs (20 kV, 400 SWs) at 0.2, 0.5, 1, and 2 Hz in a research electrohydraulic lithotripter. Fragmentation was assessed by measuring number, size, and projected surface area of the fragments. Stones treated at 0.2 Hz exhibited significantly greater fragmentation (p<0.01) than stones at 1 or 2 Hz, while fragmentation between 0.2 and 0.5 Hz was similar. Mean ± SEM for fragment area increase was 370±53% at 0.2 Hz (n=10 stones), 280±34 at 0.5 Hz (8), 130±31 at 1 Hz (5), and 101±16 at 2 Hz (20). This pronounced enhancement of fragmentation at very slow SW rate was unexpected. High-speed camera images of cavitation at solid objects show an increased bubble cloud at faster SW rates. The bubble cloud may interfere with transmission of acoustic energy to the stone surface. These in vitro data suggest the possibility that patient treatment at fast SW delivery rates may decrease the efficiency of stone comminution. [Work supported by NIH P01-DK43881.]

201 円管内オリフィス流のキャビテーション微発光領域の可視化

Light-emitting region of cavitation bubble flows generated behind an orifce in a circular pipe has been visualized by optical methods. Xenon gas wsa dissolved in clear water for enhancement of weak emission from cavitation, and its effect on the luminous properties of the flows was investigated. Spacial emission profiles and shadowgraph images of clear water and water-xenon cavitation were obtained by photon counting and and ordinary photographic methods, and compared with each other. It was found that the emission property of the water-xenon cavitation was very similar to that of clear water, and the photographic method was directly apoplicable for the orifice cavitation flow under the enhanced condition.

Approaches for TEM imaging of cavitation in toughened nylon

A controversial topic in the study of structure-property relationships of toughened polymer systems is the internal cavitation of toughener particles resulting from damage on impact or tensile deformation.Detailed observations of the influence of morphological characteristics such as particle size distribution on deformation mechanisms such as shear yield and cavitation could provide valuable guidance for selection of processing conditions, but TEM observation of damaged zones presents some experimental difficulties.Previously published TEM images of impact fractured toughened nylon show holes but contrast between matrix and toughener is lacking; other systems investigated have clearly shown cavitated impact modifier particles. In rubber toughened nylon, the physical characteristics of cavitated material differ from undamaged material to the extent that sectioning of heavily damaged regions by cryoultramicrotomy with a diamond knife results in sections of greater than optimum thickness (Figure 1). The detailed morphology is obscured despite selective staining of the rubber phase using the ruthenium trichloride route to ruthenium tetroxide.