Papers by Keyword: Cavitation

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Authors: Yong Chen, He Zhang, Shao Jie Ma
Abstract: The external turbine can be used on underwater high-speed moving body to measure its own velocity. By establishing the rotating turbine dynamic equations and using UDF programming for secondary development on fluent software, the three-dimensional dynamic simulation of water speed measurement turbine model was achieved. Using this model, under the complex flow environment like cavitation and small attack angle, the dynamics simulation was performed and the results was analyzed to get the turbine movement characteristics. Simulation results show that the simulation model can reflect the variation in characteristics of the turbine caused by the small attack angle at cavitation situation.
Authors: Hajime Iwasaki, Toru Mori, Mamoru Mabuchi, Kenji Higashi
Authors: Jing Hao Li, Xiang Feng Liu, Wei Feng Huang, Yu Ming Wang
Abstract: A finite element cavitation algorithm to Reynolds equation is presented for the calculation of the flow field in the film between the faces of the mechanical seal. As using free mesh, the algorithm is particularly useful for the computational domain which shape is complex. The JFO boundary condition which satisfies mass conservation is implemented by introducing Kumar and Booker’s algorithm. A non-traditional finite element method is derived to avoid the process of the functional analysis and can obtain the flow rate on boundaries conveniently. The results show that the algorithm is reliable, effective and correspond to the literature results. Moreover, the algorithm can be also used for the sliding bearings lubrication problem which shows the well adaptability.
Authors: Feng Luo, Xiao Li Zhang
Abstract: This paper aims to bring an organized overview of the damper malfunction due to the cavitation and aeration phenomena, which are normal problems for all kinds of hydraulic dampers. The object of this report is to describe, detect and simulate these damper failures.
Authors: Yoshinobu Motohashi, Makoto Kikuchi, Takaaki Sakuma, Eitaro Yukutake, Isao Kuboki
Abstract: During superplastic deformation (SPD) of tetragonal zirconia polycrystals containing 3 mol% yttria (3Y-TZP) at high strain-rates, a number of crack-like flat cavities having very narrow gaps lying along grain boundaries mostly normal to the tensile axis are produced in addition to conventional cavities. The formation and growth of these flat cavities are responsible for the strain softening that appears on the true stress versus true strain curves. The growth and coalescence of the flat cavities were a main cause of the degradation of elongation to fracture. We have found that a simple treatment, in which the superplastic deformation is temporally stopped, i.e., the cross-head movement is reversed and accordingly the applied load is removed, and then the specimen is kept at the test temperature for several minutes, is surprisingly effective to reduce the flat cavities. Carrying out this simple treatment repeatedly, after 30% nominal stain during the SPD, led to an increace in total elongation by about three times larger than that of a specimen not subjected to such a treatment. This treatment can also recover the strength and accordingly mechanical properties of the superplastically deformed 3Y-TZP to that of the undeformed state. This finding is believed to be quite significant for practical applications of superplasticity in 3Y-TZP, because the flat cavities can be closed very simply by keeping a product at the forming temperature after or during the superplastic forming process.
Authors: Zhi Yong Dong, Yong Gang Yang, Qi Qi Chen, Bin Shi
Abstract: This paper experimentally investigated hydraulic characteristics in working section of multi-square-hole orifice plates of hydrodynamic cavitation reactor by use of three-dimensional Particle Image Velocimetry (PIV) and High Speed Photography etc. Arrangements of holes in the orifice plates can be divided into diagonal, cross and checkerboard categories. The three-dimensional velocity distribution, pressure and cavitation characteristics for each arrangement of multi-hole orifice plates were measured by PIV system, pressure data acquisition system and high speed camera, and a comparison of hydraulic characteristics of the three categories of arrangements of the multi-hole orifice plates were made.
Authors: Robert Mettin, P.E. Frommhold, X. Xi, F. Cegla, H. Okorn-Schmidt, A. Lippert, F. Holsteyns
Abstract: Applications of acoustic cavitation [ frequently suffer from certain random aspects (e.g., stochastic bubble nucleation events) as well as from its sensitivity to external parameters (like gas content in the liquid). This renders for example a prediction of bubble distributions in size and space still a difficult task. To improve this situation by a better understanding of the fundamentals, a "bottom-up" approach has recently been followed which tried to model collective bubble phenomena and bubble structures on the basis of single bubbles and their interaction [. If the behavior of individual bubbles can be well captured by the models, it is hoped to gain significant insight into a larger system of acoustically driven bubbles. Indeed, several aspects of multi-bubble systems and structures could be explained by single bubble dynamics, for instance by the inversion of the primary Bjerknes force in strong ultrasonic fields. Nevertheless, many details of bubble dynamics stay partly unclear, and considerable efforts are undertaken to improve our understanding and to optimize applications of acoustic bubbles.
Authors: Bong Kyun Kang, Ji Hyun Jeong, Min Su Kim, Hong Seong Sohn, Ahmed A. Busnaina, Jin Goo Park
Abstract: As the semiconductor manufacturing technology for ultra-high integration devices continue to shrink beyond 32 nm, stringent measures have to be taken to get damage free patterns during the cleaning process. The patterns are no longer cleaned with the megasonic (MS) irradiation in the advanced device node because of severe pattern damages caused by cleaning. Recently, several investigations are carried out to control the cavitation effects of megasonic to reduce the pattern damages. The mechanism of damage caused by an unstable acoustic bubble motion was mainly attributed to the high sound pressure associated with violent bubble collapse [1]. In order to characterize the dominant factors affecting the cavitation, MS cleaning was conducted with various dissolved gas concentrations in water. It was reported that the cavitation phenomena relating to particle removal efficiency (PRE) and pattern damage were considerably changed with the addition of a specific gas [2]. This changing behavior may be due to the difference in the physical properties of dissolved gases associated with acoustic bubble growth rate as a function of their concentration. In particular, cavitation effects induced during MS cleaning was controlled by adjusting the acoustic bubble growth rate. Also the change of bubble growth rate is well explained by both rectified diffusion for single bubble and bubble coalescence for multi-bubble, respectively. Similarly, it is well-known that surface active solute (SAS) in the ultrasound field plays an important role in controlling the cavitation effects. A detailed explanation of the acoustic bubble growth rate, cavitation threshold and their relationship with various types of SAS and concentration of biomedical and chemical reactions perspective have been reported elsewhere [3,4]. Their studies demonstrated that the change of cavitation effects depends not only on the chain length of alcohol in the solution but also on the physical properties such as surface tension and viscosity of SAS solutions.
Authors: G. Kumaresan, K. Kalaichelvan
Abstract: Superplasticity is the ability of a polycrystalline material to exhibit, very large elongations without necking prior to failure in generally isotropic manner. Elongations in excess of 400% are usually referred to as Superplasticity. As the limitations of sheet metal fabrication are most often determined by the tensile ductility, superplasticity in sheet metals offers advantages for the forming of complex shapes easily as a regular production process.The focus of the present work is to arrive at the optimum process parameters in the superplastic forming in re-entrant shape of 7075 aluminium alloy, so as to achieve minimum thinning, lesser forming time and reduction in micro cavities.
Authors: Megumi Kawasaki, Cheng Xu, Terence G. Langdon
Abstract: A commercial aluminum 7034 alloy, produced by spray casting and having an initial grain size of ~2.1 μm, was subjected to equal-channel angular pressing (ECAP) through six passes at 473 K. In the as-pressed condition, the microstructure was reasonably homogeneous and the grain size was reduced to an ultrafine grain size of ~0.3 μm. This alloy contains MgZn2 and Al3Zr precipitates which restrict grain growth. In tensile testing at 673 K after processing by ECAP, an elongation of >1000% was achieved at a strain rate of 1.0 × 10-2 s-1 corresponding to high strain rate superplasticity. Quantitative cavity measurements were conducted on the specimens after tensile testing for both the as-received condition and after ECAP. These measurements reveal a significant number of small cavities in the samples and especially in the sample that exhibited a very high elongation. This paper describes the morphology of cavity development in the spray-cast aluminum alloy in both the as-received and as-pressed condition.
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