Interaction of particles with a cavitation bubble near a solid wall

Hard particle erosion and cavitation damage are two main wear problems that can affect the internal components of hydraulic machinery such as hydraulic turbines or pumps. If both problems synergistically act together, the damage can be more severe and result in high maintenance costs. In this work, a study of the interaction of hard particles and cavitation bubbles is developed to understand their interactive behavior. Experimental tests and numerical simulations using computational fluid dynamics (CFD) were performed. Experimentally, a cavitation bubble was generated with an electric spark near a solid surface, and its interaction with hard particles of different sizes and materials was observed using a high-speed camera. A simplified analytical approach was developed to model the behavior of the particles near the bubble interface during its collapse. Computationally, we simulated an air bubble that grew and collapsed near a solid wall while interacting with one particle near the bubble interface. Several simulations with different conditions were made and validated with the experimental data. The experimental data obtained from particles above the bubble were consistent with the numerical results and analytical study. The particle size, density and position of the particle with respect to the bubble interface strongly affected the maximum velocity of the particles

Two-phase velocity measurement in a particle-laden jet

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Multiphase Hydrodynamics In Steady And Pulse Jet Mixing Systems

The goal of the present study is to evaluate the mixing performance of jet mixers in both liquid and solid-liquid mixing processes. Jet mixers have been studied for decades for its uses in liquid blending and solid-liquid mixing applications. In solid suspension processes, jet mixers can be just as useful if not more useful than conventional impeller mixers. However, there is a lack of phenomenological models that exist. The erosion and subsequent suspension of solids beds, as well as the suspension of a low concentration of solid particles must be better understood. The specific objectives were to develop analytical, experimental and numerical models that simulate a liquid, submerged, steady or pulsing jet mixer. Furthermore, specific objectives were to determine the performance of jet mixers in solid suspension processes by measuring the cloud height, develop a model that describes the erosion of a solids bed, and determine the effect of cohesive particles on the dispersion of particles once eroded. The results showed that the mixing performance, in terms of mixing time, was not enhanced with the use of pulsing jet flows. The results showed that the cloud height below about 24000 is not dependent on the jet Reynolds number. The erosion profiles of solids were found for solids beds composed of particles with different Archimedes numbers and results showed that there appears to be two different regimes present. The regimes occur based on the erosion mechanisms that are taking place, mainly entrainment and surface erosion. Results of the axial concentration studies showed that the time dependence of the concentration ceases to exist after a certain period, which is a function of the weight percent of cohesive particles

Development of a new erosion apparatus for gravel materials

Orientadores: José Gilberto Dalfré Filho, Stefano MalavasiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e UrbanismoResumo: O Brasil detém grande parte da água doce do mundo, garantindo um grande potencial hidrelétrico, dada a grande e crescente demanda por energia elétrica renovável da atualidade. Grande parte das usinas hidrelétricas foram construídas nas décadas de 1950 a 1980 e já apresentam necessidade de reparos das estruturas de concreto. Dentre os danos sofridos por essas estruturas, neste trabalho é discutida a erosão. Além disso, grande parte das usinas a serem construídas são planejadas para a região norte do país, onde há grande concetração de sólidos carreados pela água dos rios. Em estruturas hidráulicas, a erosão pode causar danos irreversíveis. Esforços constantes em pesquisas qualitativas e quantitativas desempenham um papel importante para definir quais são os materiais mais confiáveis e seguros. Estudos anteriores destacam a necessidade de se desenvolver um novo modelo de erosão do concreto em estruturas hidráulicas em uma abordagem realista, através da simulação do ambiente onde ocorre a erosão. Neste sentido, existem poucos estudos que enfatizam a importância da erosão sobre superfícies de concreto causada por sólidos transportados no fluxo de água, como em galerias de água, vertedouros e bacias de dissipação. Neste estudo, apresentamos um novo aparato para testar concretos. Este dispositivo foi desenvolvido adaptando um modelo proposto pela ASTM C1138 para ter uma metodologia mais próxica ao fenômeno real. Os resultados mostraram uma nova abordagem para solucionar o problema da erosão. Paralelamente a isso, foi feita uma análise fluido-dinâmica através de um modelo CFD, simulando as condições deste novo aparato, permitindo a comparação com resultados numéricos. Esta comparação mostrou consistência para o modelo escolhido, confirmando a escolha dos parâmetros de operaçãoAbstract: Brazil holds a large part of the world's fresh water supply, guaranteeing a great hydroelectric potential, given the currently large and growing demand for renewable electricity. Most hydroelectric plants, built in the years between 1950 and 1980, already require repairs of concrete structures. Among damages in these structures, erosion is the most severe. In addition, most plants are planned for the northern region of the country, where there is a large concentration of solids carried by river water. In hydraulic structures, erosion can cause irreversible damage. Constant efforts in qualitative and quantitative research play an important role in defining which materials are the most reliable and safe. Previous studies have highlighted the need to develop a new concrete erosion model in hydraulic structures, with a realistic approach by simulating the environment where erosion occurs. In this sense, there are few studies that emphasize the importance of erosion on concrete surfaces caused by solids transported in the water flow, such as in water galleries, spillways and dissipation basins. In this study, we present a new apparatus for testing concrete. This device was developed by adapting a model proposed by ASTM C1138 to allow a methodology closer to the real phenomenon. The results show a new approach for solving the erosion problem. Parallel to this, a fluid-dynamic analysis was performed through a CFD model, simulating the conditions of this new apparatus, allowing the comparison with numerical results. This comparison showed consistency for the chosen model, confirming the choice of operating parametersMestradoRecursos Hidricos, Energeticos e AmbientaisMestre em Engenharia Civil01-P-01879-2016CAPE

Experimental Investigation and Modelling of Sand Jets Passing through an Immiscible Layer

Sand jets passing through two immiscible liquids, water and oil have many applications in the field of civil and environmental engineering such as tailings transport, dredging and discharge of industrial and urban wastewater. Understanding the dynamic interactions of the sand particles and its ambient are important for proper design and optimizing the engineering systems. Mass, momentum and energy of the system can be influenced by interactions of the suspended particles within the jet. The conducted experimental studies and numerical and nominal modeling in this thesis are new in terms of the fundamental understanding of jet characteristics. Part of this thesis focused on the experimental parameters and characteristics of oily sand jets such as frontal width and velocity. Effects of the controlling parameters of the oily sand jets such as nozzle diameter, oil layer thickness and mass were investigated and it was found that the effect of nozzle diameter on evolution of oily sand jets was more significant than the other parameters. Study in water phase, it was observed that the bursting of a group of particles covered with a thin oil layer can be classified into three different forms. Evolution of trailing waves of the oily sand jets and their characteristics such as wave length and wave amplitude were also investigated. Part of this thesis focused on Data mining and boundary visualization techniques to study the effects of experimental parameters on the shapes of oily sand jets. Model trees were developed to classify and predict the growth of oily sand jets at different conditions. It was found that the model tree can predict the growth of sand jets with an uncertainty of ±8.2%, ±6.8% and ±8.7% for width, velocity and distance from the nozzle, respectively. The main aim of this thesis is to explore and find correlations between the dynamics of sand particles through passing oil-water interface and controlling parameters such as nozzle diameter, oil layer thickness and mass of sand particles. Therefore, it was found that the nozzle size has significant effect on characteristics of evolution of oily sand jets such as frontal velocity, development of bursting, formation of trailing wave section and shear stress in comparison with other controlling parameters such as oil layer thickness and mass of sand particles. Investigation of formation of frontal shapes of oily sand jets in water indicates the fate of sand jets after passing an immiscible interface and sedimentation of sand particles. The main controlling parameter for evolution of various shapes of oily sand jets front is the nozzle diameter. Mass of sand particles and oil layer thickness are the secondary and tertiary important parameters. Evolution of different frontal shapes of oily sand jets can also change specific characteristics of oily sand jets such as frontal velocity and width. In terms of environmental analysing formation of various shapes of oily sand jets can explain variations of velocity of sediments and under which conditions these sediments spread or deposit without dispersion in oceans

Fluid Mud Underflows in Coastal Dredge Disposal

This manuscript presents the results of a thorough theoretical and experimental investigation on fluid mud underflows generated in a typical coastal dredge disposal operation. The main goal of this investigation is to understand the propagation dynamics of fluid mud underflows that depends upon a number of factors, including: concentrations, rheological properties and released configurations of fluid mud. Laboratory experiments were conducted with different initial fluid mud concentrations in three different experimental set-ups: rectangular flume for constant volume release, rectangular flume for constant flux release, and a square pool for radial constant flux release of fluid mud. The experiments in the rectangular flume generated two-dimensional underflows. The experiments in the pool simulated typical open water pipeline disposal operations with submerged vertical discharge configuration in the field and radially axisymmetric three-dimensional fluid mud underflows were generated in these experiments. As expected, constant volume release experiments generated gravity currents that exhibit slumping, inertial and viscous propagation phases while constant flux release experiments generated initial horizontal buoyant jets which then transform into gravity currents that exhibit inertial and viscous propagation phases. The experiments showed that the propagations of underflows were significantly influenced by the non-Newtonian rheology of released fluid mud. Underflows formed by initial low concentration of fluid mud release did not experience the viscous propagation phase in the limited experimental set-ups that were used in the experimental investigation. However, high concentration fluid mud releases rapidly transitioned into viscous propagation phase, sometimes even bypassing the expected inviscid phase. The inter-transitions of propagation phases were determined from experimental data and they were related to the initial source parameters by deriving order-of-magnitude expressions for transitions. The theoretical part of this investigation also includes experimental evaluation of three mathematical modeling approaches to model the inertial and viscous propagation of fluid mud gravity currents. These three mathematical modeling approaches are, from simplest to the most complex: force-balance, box model and shallow water/lubrication theory approximation. The force-balance and box model solutions for viscous propagation of non-Newtonian gravity currents were non-existent and hence, derived in this investigation. For the inertial propagation of fluid mud gravity currents, it was concluded that box model would be the most efficient analytical model due to its closed-form solution for all of the release configurations, and its predictive accuracy (based upon its experimental evaluation and inter-comparison of the models). For the viscous propagation, self-similar solution based on the lubrication theory approximation would be the better choice. However, only box model solution can provide analytical solution for all possible release configurations which make it a good alternative, especially for quick predictions. The results of this study are expected to be useful for predicting the temporal fate of fluid mud underflows in coastal dredge disposal operations

In situ characterization of mixing and sedimentation dynamics in an impinging jet ballast tank via acoustic backscatter

Impinging jets are utilized in numerous applications, including nuclear waste treatment, for both the erosion of sediment beds and maintaining particulates in suspension. Pulse-echo ultrasonic methods offer great potential for the in situ monitoring of critical mixing and settling dynamics, in concentrated dispersions. A non-active scaled version of a Highly Active Storage Tank at Sellafield, UK, was profiled with an acoustic backscatter system under various jet firing conditions. An advanced analysis technique enabled the direct quantification of dispersion concentration changes from the converted backscatter attenuation. Hence, the erosion and mixing capability of the jets, and settling kinetics were characterized. It was found that jet operation alone provided inadequate localized mixing of eroded sediment. An additional air-lift process operation was required to hinder the rapid re-settling of dispersed particulates

Particle Jetting Induced by the Impulsive Loadings

Particle rings/shells/cylinders dispersed by the radial impulsive loadings ranging from strong blast waves to moderate shock waves form a dual coherent jetting structure consisting of particle jets which have different dimensions. In both circumstances, the primary jets are found to initiate from the inner surface of particle layers and propagate through the thickness of particle layers, which are superimposed by a large number of much smaller secondary jets initiating from the outer surface of particle layers upon the reflection of the shock wave. This chapter first presents a summary of the experimental observations of the hierarchical particle jetting mainly via the cinematographic techniques, focusing on the characteristics of the primary particle jet structure. Due to the distinct behaviors of particles subjected to the strong blast and moderate shock waves, specifically solid-like and fluid-like responses, respectively, the explosive and shock-induced particle jetting should be attributed to distinct mechanisms. A dual particle jetting model from the perspective of continuum is proposed to account for the explosive-induced particle jetting. By contrast the shock-induced particle jetting arises from the localized particle shear flows around the inner surface of particle layers which result from the heterogeneous network of force chains

Flow characteristics study of fly ash slurry in hydraulic pipelines using computational fluid dynamics

Transportation of fly ash slurry via pipelines has been recognized as a potential economical and dependable mode of solid transportation. It also bids various other advantages over the conventional means of transportation. For improved understanding of the flow characteristics of these pipelines, investigators throughout the world have been analyzing the flow experimentally numerically and theoretically. Slurry pipeline systems are regularly used crosswise the world for the transportation of fly ash from the power plant to the ash ponds. These pipeline are very much energy exhaustive and also leads to disproportionate and inordinate wear of pipelines and wastage of water. Objective of the present work is to conduct a methodical and logical study of fly ash slurry transportation in a pipeline at higher concentrations by the use of computational fluid dynamics and study the flow characteristics and pressure drops. An effort has been made in this study to develop comprehensive slurry flow model using CFD and utilize the model to predict pressure drop and validating the results with the calculated results. A broad computational fluid dynamics (CFD) model was established in the current study to gain understanding into the solid liquid slurry flow in pipelines. The approach adopted in here is studying and solving the problem by mathematical modeling method. In this work, the solid suspension in a fully developed pipe flow was simulated and analyzed A 20m pipe with a diameter of 0.5m is modeled, through which flow is conducted where modelling and meshing is done using ANSYS Fluent. High viscosity fly ash slurry with five different concentrations, 50%, 60%, 65%, 68% and 70% by weight of fly ash is passed and for each concentration five different velocities like 3, 3.5, 4, 4.5 and 5 m/s are used and pressure drops are calculated. Other characteristics studied are volume fraction, eddy viscosity and turbulence kinetic energy