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Improvement of the cavitation erosion resistance of UNS S31803 stainless steel by duplex treatment

MESA, D. H.; Pinedo, Carlos Eduardo; Tschiptschin, Andre Paulo
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.27%
A duplex surface treatment consisting of High Temperature Gas Nitriding (HTGN) followed by Low Temperature Plasma Nitriding (LTPN) was carried out in an UNS S31803 duplex stainless steel. The HTGN treatment was intended to produce a relatively thick and hard fully austenitic layer giving mechanical support to the thinner and much harder expanded austenite layer. HTGN was performed at 1200 degrees C for 3 h, in a 0.1 MPa N(2) atmosphere while LTPN, was carried out in a 75% N(2) + 25% H(2) atmosphere, at 400 degrees C for 12 h, under a 250 Pa pressure, and 450 V. An expanded austenite gamma(N) layer, 2.3 mu m thick, 1500 HVO.025 hard, was formed on top of a 100 mu m thick, 330 HV 0.1 hard, fully austenitic layer, containing 0.9 wt% N. For comparison purposes LTPN was carried out with UNS S30403 stainless steel specimens obtaining a 4.0 mu m thick, 1500 HV 0.025 hard, expanded austenite layer formed on top of a fully austenitic matrix having 190 HV 0.1. The nitrided specimens were tested in a 20 kHz vibratory cavitation-erosion testing equipment. Comparison between the duplex treated UNS S31803 steel and the low temperature plasma nitrided UNS S30403 steel, resulted in incubation times almost 9 times greater. The maximum cavitation wear rate of the LTPN UNS S30403 was 5.5 g/m(2)h...

Mesoscale plasticity anisotropy at the earliest stages of cavitation-erosion damage of a high nitrogen austenitic stainless steel

Grajales, Dairo Hernan Mesa; Ospina, Carlos Mario Garzon; Tschiptschin, Andre Paulo
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.27%
A high nitrogen austenitic stainless steel (0.9wt% N) and an ordinary 304 austenitic stainless steel were submitted to cavitation-erosion tests in a vibratory apparatus operating at a frequency of 20 kHz. The high nitrogen stainless steel was obtained by high temperature gas nitriding a 1-mm thick strip of an UNS 31803 duplex stainless steel. The 304 austenitic stainless steel was used for comparison purposes. The specimens were characterized by scanning electron microscopy and Electron Back Scatter Diffraction. The surface of the cavitation damaged specimens was analyzed trying to find out the regions where cavitation damage occurred preferentially. The distribution of sites where cavitation inception occurred was extremely heterogeneous, concentrating basically at (i) slip lines inside some grains and (ii) Sigma-3 coincidence site lattice (CSL) boundaries (twin boundaries). Furthermore, it was observed that the CE damage spread faster inside those grains which were more susceptible to damage incubation. The damage heterogeneity was addressed to plasticity anisotropy. Grains in which the crystallographic orientation leads to high resolved shear stress show intense damage at slip lines. Grain boundaries between grains with large differences in resolved shear stress where also intensely damaged. The relationship between crystallite orientation distributions...

Efeitos da pressão do sistema de arrefecimento e da concentração de etilenoglicol sobre as características de cavitação de uma bomba d'água automotiva.; Effects of cooling system pressure and ethyleneglycol concentration upon water pump cavitation features.

Melo, Weber Bizarrias de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/08/2008 PT
Relevância na Pesquisa
37.09%
Este trabalho apresenta a analise do efeito da concentração da mistura etilenoglicol / água, pressão do sistema, rotação da bomba e temperatura, sobre o fenômeno cavitação em sistemas de arrefecimento, tendo dois principais objetivos: 1 Explorar as principais características do fenômeno cavitação, através da analise crítica e citação de publicações existentes; 2 Mapear as condições de trabalho de um sistema de arrefecimento, para então simular em bancada as interações da variação dos fatores citados acima, comparando os resultados com publicações já existentes, contribuindo então com um banco de dados que possibilite a otimização do dimensionamento de novos sistemas de arrefecimento.; This work presents the effect analysis of the water / ethyleneglycol mixture, system pressure, pump speed and temperature upon the cavitation phenomenon in cooling systems. Moreover, it has two main targets which are: 1 To explore the main features of the cavitation phenomenon through a critical analysis and citation of available publications; 2 To monitor the cooling system work conditions in order to simulate in a test rig the variation of the parameters described above, understanding its interaction, for than to provide a database that make possible the design optimization of new cooling systems.

Estudo dos micromecanismos de dano por cativação em aço inoxidável UNS S 31803 de alto teor de nitrogênio com e sem encruamento.; Study of micromechanics of cavitation damage in UNS S 31803 high nitrogen stainless steel with and without work hardening.

Varela Jiménez, Luis Bernardo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 04/10/2013 PT
Relevância na Pesquisa
37.32%
Neste trabalho pretende-se estabelecer relações entre a micro e a nanoestrutura e a resistência à erosão-cavitação em aços inoxidáveis com alto teor de nitrogênio. Estas relações serão determinadas através do estudo dos mecanismos de deformação plástica e degradação observado nas superfícies e na micro e nanoestrutura durante ensaios de cavitação vibracional. As amostras do aço inoxidável duplex UNS S31803, com aproximadamente 0,9% N em peso, foram obtidas por nitretação gasosa em alta temperatura, divididas em amostras com nitrogênio em solução sólida e solubilizadas e amostras com nitrogênio em solução sólida e encruadas. As amostras de ensaio foram submetidas à cavitação vibratória em água destilada. Os mecanismos de dano que operam nas diferentes etapas do desgaste foram analisados utilizando microscópio eletrônico de varredura (MEV) para diferentes tempos de ensaio, analisando sempre o mesmo local através da perda de massa. A partir dos resultados obtidos nesse trabalho, observa-se que as amostras com nitrogênio em solução sólida e solubilizadas (318HTGN+Sol), e as laminadas (318HTGN+Enc), apresentaram taxa de desgaste 16 e 172 vezes menores, respectivamente, comparadas com o aço AISI 304L solubilizado. Por outro lado...

Avaliação de um novo modelo de reator de cavitação hidrodinâmica para o aquecimento controlado de líquidos e produção de emulsões em escala sub-micrométrica.; Evaluation of new hydrodynamic cavitation reactor for controlled heat of liquids and production of sub-micrometre scale emulsions.

Santos, Marcelo Del Giudice Rocha
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/09/2014 PT
Relevância na Pesquisa
36.94%
O presente trabalho consiste na avaliação de um novo modelo de reator de cavitação hidrodinâmica pertencente à classe dos homogeneizadores de alta velocidade, comercialmente conhecidos por High Speed Homogeneizers. É sabido que esse tipo de equipamento possui um amplo leque de aplicações industriais, sendo muitas vezes constituintes de operações unitárias para emulsificação, homogeneização, síntese química, dentre outras. Neste trabalho fez-se um estudo da eficiência deste novo modelo para duas aplicações, o aquecimento controlado de líquidos e a produção de emulsões de óleo em água com diâmetros de partículas em escala sub-micrométricas. As duas aplicações foram estudadas em uma planta piloto, de onde foi possível constatar o potencial de aplicação desse novo modelo de reator, especialmente devido ao baixo custo operacional e praticidade de operação.; This work evaluates a new model of hydrodynamic cavitation reactor, which belongs to the class of high-speed homogenizers. This type of equipment has a wide range of industrial applications and it is often constituent of unit operations for emulsification, homogenization, chemical synthesis, among others. In this master thesis a study regarding the efficiency of this new model for two applications was made: the controlled heating of fluid and the production of oil in water emulsions with particle diameters in the sub-micrometer scale. The two applications were studied in a pilot plant...

NOISE GENERATED BY CAVITATION IN ORIFICE-PLATES WITH SOME GASEOUS EFFECTS.

Bistafa, S. R.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 41-52
ENG
Relevância na Pesquisa
37.27%
An experimental investigation of the noise generated by cavitation in turbulent shear flows produced by confined sharp-edge orifice-plates is reported. The acoustic source strength of cavitation was determined by means of reciprocity type measurements. Experimentally determined scaling parameters are applied to a model to prototype scaling formula derived from dimensional analysis. The proposed formula is checked experimentally. Comparative photographic observations of the cavitation patterns for two different values of gas content are presented. The observed sound reduction, that occurs when supersaturated conditions exist downstream the orifice-plates, is explained by the effects of gas diffusion into the cavitation bubbles, and by simple acoustic attenuation.

Equipamento tipo jato cavitante para avaliação de desgaste por cavitação; Cavitating jet apparatus for evaluation of cavitation erosion

Jose Gilberto Dalfre Filho
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/07/2005 PT
Relevância na Pesquisa
37.37%
O equipamento tipo jato cavitante utiliza um bocal especialmente projetado para simular o fenômeno da cavitação desgastando uma amostra em um período de tempo curto. Isso ocorre, sobretudo, devido à magnitude da velocidade. Para maior eficiência do jato cavitante é necessária uma combinação da geometria do bocal, do diâmetro do orifício e da pressão disponível. No caso das estruturas hidráulicas se verifica o efeito simultâneo do fenômeno da cavitação e do impacto de um jato de alta velocidade. O objetivo deste trabalho foi desenvolver um equipamento tipo jato cavitante para avaliar o desgaste ocasionado pela cavitação em amostras de concreto. O estudo foi realizado no Laboratório de Hidráulica e Mecânica dos Fluidos da Faculdade de Engenharia Civil. A instalação permite variar os parâmetros de ensaio, de forma a obter a máxima eficiência do equipamento e definir o comportamento da amostra. O índice de cavitação de 0,14 é adequado aos ensaios em concretos de estruturas hidráulicas. Recomenda-se uma velocidade do jato em torno de 150 m/s, a adoção de 0,05 m de distância entre o bocal e a amostra e o uso de bocal cônico de 132°, com arestas vivas. A partir dos testes realizados, sugere-se um tempo de ensaio de quatro minutos para avaliação da resistência dos materiais face à ação da cavitação. Conclui-se que o equipamento tipo jato cavitante se mostrou adequado e eficiente para avaliação do desgaste provocado pela ação da cavitação...

The influence of octyl β-D-glucopyranoside on cell lysis induced by ultrasonic cavitation

Miller, Douglas L.; Dou, Chunyan
Fonte: Acoustical Society of America Publicador: Acoustical Society of America
Tipo: Artigo de Revista Científica
Publicado em /11/2011 EN
Relevância na Pesquisa
37.4%
Octyl β-D-glucopyranoside (OGP) has been reported to completely inhibit cavitation-induced cell lysis in vitro, possibly by quenching critical free-radical effects. In this study, the influence of OGP on cell lysis in a 60 rpm rotating-tube exposure apparatus was assessed. HL-60 cell lysis was estimated with a Coulter Multisizer counter. Cavitation activity from the 2.3 MHz, 30 s duration exposures were monitored at the 1.15 MHz subharmonic. Cavitation nucleation was accomplished by addition of an ultrasound contrast agent, or by using freshly dissolved culture media. For both nucleation methods, exposures were conducted for 0–0.7 MPa peak rarefactional pressure-amplitudes with and without 5 mM OGP, and for 0.5 MPa with 0-5 mM OGP. The addition of OGP to the cell suspension medium generally had little influence on cavitation-induced cell lysis. Exposures with no rotation had reduced subharmonic and lysis for added contrast agent, but essentially no cavitation for the fresh medium. Since the decreases or increases in cell lysis found for added OGP generally were accounted for by concomitant decreases or increases in cavitation activity, the changes in cell lysis could be explained by variation of the mechanical effects of cavitation without invoking a critical role for free-radical effects.

A reduced-order, single-bubble cavitation model with applications to therapeutic ultrasound

Kreider, Wayne; Crum, Lawrence A.; Bailey, Michael R.; Sapozhnikov, Oleg A.
Fonte: Acoustical Society of America Publicador: Acoustical Society of America
Tipo: Artigo de Revista Científica
Publicado em /11/2011 EN
Relevância na Pesquisa
37.19%
Cavitation often occurs in therapeutic applications of medical ultrasound such as shock-wave lithotripsy (SWL) and high-intensity focused ultrasound (HIFU). Because cavitation bubbles can affect an intended treatment, it is important to understand the dynamics of bubbles in this context. The relevant context includes very high acoustic pressures and frequencies as well as elevated temperatures. Relative to much of the prior research on cavitation and bubble dynamics, such conditions are unique. To address the relevant physics, a reduced-order model of a single, spherical bubble is proposed that incorporates phase change at the liquid-gas interface as well as heat and mass transport in both phases. Based on the energy lost during the inertial collapse and rebound of a millimeter-sized bubble, experimental observations were used to tune and test model predictions. In addition, benchmarks from the published literature were used to assess various aspects of model performance. Benchmark comparisons demonstrate that the model captures the basic physics of phase change and diffusive transport, while it is quantitatively sensitive to specific model assumptions and implementation details. Given its performance and numerical stability, the model can be used to explore bubble behaviors across a broad parameter space relevant to therapeutic ultrasound.

Erosão, corrosão, erosão-corrosão e cavitação do aço ABNT 8550 nitretado a plasma; Erosion, Corrosion, Erosion-Corrosion and Cavitation of ABNT 8550 Plasmanitrided Steel

Silva, Flávio José da
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
37.32%
O aço ABNT 8550 é utilizado na construção de rotores de bombas multifásicas para exploração de petróleo em águas oceânicas profundas, o que justifica um estudo visando o aumento da resistência ao desgaste e à corrosão deste material. Neste trabalho, foram analisadas amostras nitretadas do aço ABNT 8550 com ênfase na resistência à erosão, corrosão, erosão associada à corrosão, e cavitação. Adicionalmente, foram avaliadas amostras nitretadas com deposição adicional de revestimentos aplicados por PVD. O procedimento experimental incluiu: a) produção e caracterização de diferentes tipos de amostras, variando-se a microestrutura do material de base (martensita revenida e ferritaperlita) e os principais parâmetros de nitretação; b) testes de corrosão em água do mar sintética sem escoamento (parada); c) a construção e avaliação de um aparato para simular a erosão e a corrosão, além da ação conjunta destes fenômenos, e d) a realização de testes de cavitação pelo método de vibração ultra-sônica. Os resultados de caracterização das amostras mostraram que um maior tempo de nitretação e maior teor de nitrogênio resultam em maiores espessuras de camadas nitretadas. Com relação à dureza máxima dessas camadas...

Aspectos operacionais de revestimentos soldados: desgaste erosivo e cavitação; Operational aspects of coatings welds: erosive wear and cavitation

Silva, Hebert Roberto da
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
37.09%
O processo de soldagem MIG/MAG com suas aplicações utilizando dois arames aponta no mercado como uma alternativa para revestimento, quando uma alta produtividade é desejada. Surgem variantes potenciais deste processo, como o MIG/MAG arame frio e MIG/MAG duplo arame. Uma das maiores dificuldades é o ajuste de seus parâmetros, que, além de duplicados em relação ao MIG/MAG convencional, agem de forma dependente. Um maior entendimento dessa tecnologia aplicada a revestimentos em diversas posições é fundamental para que se possa dominar o processo e as suas variáveis, objetivando potencializar a aplicação na indústria. Foi proposto nesse estudo uma avaliação experimental para verificar a influência de algumas das variáveis sobre o perfil do cordão e a resistência ao desgaste. Para isso, é proposto nesta tese a realização de depósitos com metal de adição em aço inoxidável AWS 308LSi e ligas de cobalto (Stellites 6 e 21) em chapas de aço ao carbono ABNT 1020 na posição plana e horizontal. Na caracterização do desgaste do revestimento utilizou-se a determinação da dureza e a topografia superficial. Conclui-se que as ligas de cobalto apresentam uma resistência superior ao dano erosivo com destaque para a liga Stellite 21 em erosão e Stellite 6 na cavitação. Em uma posição intermediária em relação ao desgaste estão as misturas de aço inoxidável austenítico e ligas de cobalto. Por isso...

First Results of Cavitation Erosion Behavior of Plasma Nitrided Niobium: Surface Modification

Kertscher,Ricardo; Moraes,Juliana Martins de; Henke,Sérgio; Allenstein,Angela Nardelli; Silva,Regis Henrique Gonçalves e; Dutra,Jair Carlos; Brunatto,Silvio Francisco
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
Relevância na Pesquisa
37.09%
This work presents the first results of the plasma nitriding study performed in pure niobium in order to increase its cavitation erosion resistance. Samples were prepared from 98.9% purity and 90% reduction cold-rolled niobium bars. Annealing treatment of the cold-worked niobium samples was carried out in vacuum furnace at 1.33 Pa pressure, in the temperature of 1000 °C, for a time of 60 min. Annealed samples showing hardness of 80 HV were cut to dimensions of 20 × 30 × 4 mm3. Nitriding treatment was conducted at 1080 °C, gas mixture of 90% N2 + 10% H2, flow rate of 5 × 10–6Nm3s–1, and pressure of 1200 Pa (9 Torr), for a total time of 4 h comprised by two treatment steps of 2 h each. For comparison purpose, results for nitrided and non-nitrided niobium are confronted. Samples were characterized by XRD, nanoindentation, microhardness, SEM, and 2D surface topography and 3D interferometry profile analysis techniques. Cavitation testing was conducted according to ASTM G32-09. Comparatively, promising results based on the formation of niobium nitride phases in treated surfaces are presented and discussed in the present work.

Fluid-interaction and cavitation effects on a surface ship model due to an underwater explosion

Santiago, Leonard D.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: ix,136 p.
EN_US
Relevância na Pesquisa
37.09%
Approved for public release; distribution is unlimited.; A surface ship subjected to an underwater explosion is exposed to shock waves over a short period of time which can vary in magnitude based on charge type, size, and location. The energy of those waves impinging upon the hull is transmitted throughout the ship's structure and vital equipment. The dynamics of the shock waves also influence the fluid surrounding the outer hull of the ship, creating an area of cavitating fluid. The combination of the shock waves, bubble pulsations, and cavitating fluid induce shipwide vibrations on hull supports and mission essential equipment which may become inoperative. In view of congressional requirements for new ship designs and systems to be shock tested, this thesis investigates the modeling of a preliminary design (Flight I) of the Arleigh Burke Destroyer (DDG 51) exposed to an underwater explosion. The effects of cavitation on one and two dimensional models is explored to determine if cavitation effects are substantially important to a three dimensional ship model. Validation of modeling underwater explosion effects upon a ship model can provide potential insight and savings in cost for future live fire testing and evaluation of the Flight IIA (DDG 79) design of the Arleigh Burke Destroyer.; http://archive.org/details/fluidinteraction00sant; Lieutenant...

A theory for cavitation in impellers

Garrison, C. J. (Clarence Jimmy)
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório
ENG
Relevância na Pesquisa
37.09%
An approximate theory for cavitation in pump impellers is developed on the basis of a one-dimensional potential flow model. The theory incorporates the unsteady term occurring in Bernoulli's equation and accounts for blockage effects due to vane thickness. A comparison of the theoretical results with experimental data from mixed flow impeller tests shows good agreement near the condition of zero incidence. On the basis of the theoretical results a mechanism of cavitation breakdown is proposed. (Author); supported by various Department of Defense activities and the National Science Foundation; http://archive.org/details/theoryforcavitat00garr

Development of algorithm based on the fractional time step for the simulation of cavitation.

CHEBLI, Rezki; COUTIER-DELGOSHA, Olivier; AUDEBERT, Bruno
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
Relevância na Pesquisa
37.19%
Cavitation is one of the most demanding physical phenomena influencing the performance of hydraulic machines. It is therefore important to predict correctly its inception and development appearance, and quantify the performance losses associated with it. The objective of the simulations is to predict the instabilities associated with the presence of cavitation. The aim of this work is to develop a semi-compressible cavitating algorithm based on the fractional step method in Code_saturne. An implicit solver, based on a transport equation of void fraction coupled with the Navier-Stokes equations is proposed. Specific treatment of cavitation source terms provides physical values of the void fraction (between 0 and 1) without any numerical limitation. The influence of the turbulence models is also studied. To do this, several turbulence models are tested and compared. The instabilities due to three-dimensional effects are particularly analyzed. This work allows obtaining a numerical tool, validated for complex cavitating flows configurations, in order to improve the understanding of the physical mechanisms that control the three-dimensional unsteady effects involved in the mechanisms of instability.

Numerical modeling of the ultrasonic cavitation field and experimental evaluation of bubble density

Dubus, Bertrand; Granger, C.; Mosbah, P.; Moussatov, A.; Schmit, H.; Sztor, L.; Campos-Pozuelo, Cleofé
Fonte: Sociedad Española de Acústica Publicador: Sociedad Española de Acústica
Tipo: Comunicación de congreso Formato: 104694 bytes; application/pdf
ENG
Relevância na Pesquisa
37.09%
6 pages.-- PACS nr.: 43.35 Ei.-- Communication presented at: Forum Acusticum Sevilla 2002 (Sevilla, Spain, 16-20 Sep 2002), comprising: 3rd European Congress on Acoustics; XXXIII Spanish Congress on Acoustics (TecniAcústica 2002); European and Japanese Symposium on Acoustics; 3rd Iberian Congress on Acoustics.-- Special issue of the journal Revista de Acústica, Vol. XXXIII, year 2002.; A numerical model of ultrasonic cavitation field is described. It is based on a phenomenological description of a cavitating fluid as a non linear fluid whose characteristics (sound speed, density) depend upon the bubble density. To obtain the constitutive relationship between bubble density and acoustic pressure, a real-time measurement method of the bubble density, relying upon the variation of the electrical resistance of the medium, is proposed. The finite element formulation of the model is derived and implemented in the ATILA code. Computational results on the cavitation field created by a cylindrical concentrator are presented.; This work was supported by CNRS and CSIC (French-Spanish cooperation project #7967) and by the European Union (Feder-Retex II).; Peer reviewed

Experimental observation of nonlinear self-focusing in the cavitation field

Campos-Pozuelo, Cleofé; Granger, C.; Vanhille, Christian; Dubus, Bertrand
Fonte: Sociedad Española de Acústica Publicador: Sociedad Española de Acústica
Tipo: Comunicación de congreso Formato: 7285 bytes; application/pdf
ENG
Relevância na Pesquisa
37.19%
Ponencia presentada en el XIX Congreso Internacional de Acústica (ICA2007), Madrid, 2-7 Sep 2007.-- PACS: 43.25.Yw.; The nonlinear self-focusing of the pressure field with onset of cavitation is experimentally and theoretically analysed in the kHz range. Self-focusing in the cavitation field has already been reported above 500 kHz and it was attributed to the non-uniformity of bubble density. In this case, bubble density remains small, non-linearity is weak and focal distance remains much larger than the acoustic wavelength in the liquid.; In this work, inertial cavitation field radiated by a 20 kHz sonotrode-type transducer is considered. A cone like bubble structure is established. This structure is very repetitive and selfconstructs in any container when a piston like emitter is used. The acoustic field is directly evaluated by using a BR&K. hydrophone and averaged pressure waveforms are analysed. The number of chosen samples is high enough to have stable measured pressure results (including nonlinear distortion). A self-focusing effect is observed with a focal distance comparable to the acoustic wavelength in the liquid. Models accounting for the high bubble density and strong non-linear effects are proposed. Theoretical predictions are compared to experiments and discussed.; Peer reviewed

Cavitation scaling experiments with headforms : bubble dynamics

Kuhn de Chizelle, Yan; Ceccio, Steven L.; Brennen, Christopher E.; Shen, Young
Fonte: International Symposium on Propeller and Cavitation Publicador: International Symposium on Propeller and Cavitation
Tipo: Book Section; PeerReviewed Formato: application/pdf
Publicado em /09/1992
Relevância na Pesquisa
37.4%
Utilizing some novel instrumentation which allowed detection and location of individual cavitation bubbles in flows around headforms. Ceccio and Brennen (1991 and 1989) recently examined the interaction between individual bubbles and the structure of the boundary layer and flow field in which the bubble is growing and collapsing. They were able to show that individual bubbles are often fissioned by the fluid shear and that this process can significantly effect the acoustic signal produced by the collapse. Furthermore they were able to demonstrate a relationship between the number of cavitation events and the nuclei number distribution measured by holographic methods in the upstream flow. More recently Kumar and Brenncn (1991-1992) have closely examined further statistical properties of the acoustical signals from individual cavitation bubbles on two different headformsm in order to learn more about the bubble/flow interactions. However the above experiments were all conducted in the same facility with the same size of headform (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified in those earlier experiments change with changes of speed...

Adaptable Design Improvements For Electromagnetic Shock Wave Lithotripters And Techniques For Controlling Cavitation

Smith, Nathan Birchard
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2012
Relevância na Pesquisa
37.37%

In this dissertation work, the aim was to garner better mechanistic understanding of how shock wave lithotripsy (SWL) breaks stones in order to guide design improvements to a modern electromagnetic (EM) shock wave lithotripter. To accomplish this goal, experimental studies were carefully designed to isolate mechanisms of fragmentation, and models for wave propagation, fragmentation, and stone motion were developed. In the initial study, a representative EM lithotripter was characterized and tested for in vitro stone comminution efficiency at a variety of field positions and doses using phantom kidney stones of variable hardness, and in different fluid mediums to isolate the contribution of cavitation. Through parametric analysis of the acoustic field measurements alongside comminution results, a logarithmic correlation was determined between average peak pressure incident on the stone surface and comminution efficiency. It was also noted that for a given stone type, the correlations converged to an average peak pressure threshold for fragmentation, independent of fluid medium in use. The correlation of average peak pressure to efficacy supports the rationale for the acoustic lens modifications, which were pursued to simultaneously enhance beam width and optimize the pulse profile of the lithotripter shock wave (LSW) via in situ pulse superposition for improved stone fragmentation by stress waves and cavitation...

Mechanism of Low-Threshold Hypersonic Cavitation Stimulated by Broadband Laser Pump

Bunkin, N; Lobeyev, A; Lyakhov, G; Ninham, Barry
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.09%
The excitation of hypersonic waves prompted by a stimulated Brillouin scattering (SBS) mechanism was investigated for low threshold acoustic cavitation. The efficiency of SBS in prompting hypersonic wave excitation declines when there is a shift from practically monochromatic pumping to broadband pumping. Cavitation was observed at low intensities of acoustic pressure. This observation is attributed to the presence of fixed sized nanobubbles in the liquid.