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Innovative pre-treatment methods applied to anaerobic digestion (AD) have developed to enhance the methane yields of food waste. This study investigates hydrodynamic cavitation, which induce disintegration of biomass through microbubble formations, impact on food waste solubilisation and methane production during following AD. Two different sub-streams of food waste (before and after the digestion) pre-treated by hydrodynamic cavitation were evaluated in lab scale for its potential for implementation in a full scale practise. First, the optimum condition for the hydrodynamic cavitation device was determined based on the solids and chemical changes in the food waste. The exposure time was referred to as the number of cycles that the sample was recirculated through the cavitation inducer’s region. The optimal cycles were later tested as a pre-treatment step in a BMP test and semi-CSTR lab scale operation. The tests showed that sufficient impact from the hydrodynamic cavitation was achieved by 20 cavitation cycles. Due to the pre-treatment, food waste solubilisation increased, up to 400% and 48% in terms of turbidity and sCOD measurements, respectively. In the BMP test, the treated samples improved the methane yield by 9-13%, where the digested food waste increased its kinetic constant by 60%. Fresh food waste was then processed in the semi-CSTR operation and the methane yield was increased by up to 17% with hydrodynamic cavitation for two reference periods. These promising results suggest that the hydrodynamic cavitation can be implemented for full scale production with food waste.

L'application d'ultrasons sur une tumeur, où des liposomes se sont accumulés, permet potentiellement de libérer le médicament mais aussi d'en favoriser l'absorption dans les cellules. La cavitation inertielle ultrasonore est le phénomène pressenti pour la libération sous ultrasons de médicament encapsulé dans de petits liposomes solides. Elle est très dépendante des conditions expérimentales et peut-être intense et imprévisible. L'objectif principal du travail réalisé dans le cadre de cette thèse est de contrôler et quantifier la cavitation inertielle, pour induire le largage de médicaments encapsulés dans des liposomes. Dans cette optique, une dose de cavitation inertielle (DC), basée sur le filtrage du bruit large bande émis lors de ce régime de cavitation, est mise au point in vitro pour suivre le largage de médicament encapsulé. Sous divers régimes d'ultrasons pulsés, la DC a été validée en dosant chimiquement les radicaux hydroxyles générés lors de l'implosion des bulles. Les tests menés sur diverses formulations de liposomes contenant de la doxorubicine (dox) ont montrés une haute corrélation entre le taux de largage de dox et la DC permettant de conclure que la cavitation inertielle est impliquée dans ce largage. Le rôle de la température sur la production de radicaux hydroxyles et la libération de dox a également été exploré. Les expériences réalisées ont permis de sélectionner les formulations les plus sensibles aux ultrasons pour les tester sur des rats implantés avec des tumeurs prostatiques. Après plusieurs expériences in vivo menées avec différents dispositifs ultrasonores et formulations de liposomes, le bénéfice du traitement combiné a pu être démontré. / The sonication of a tumor, where liposomes have been accumulated, allows potentially to release encapsulated drug and to promote its absorption in cells. Ultrasonic inertial cavitation is supposed to be implicated in the release of drug encapsulated in small solid liposomes under ultrasonic exposure. Inertial cavitation is strongly dependent on experimental conditions and can be very intense and unpredictable. The main objective of this thesis was to control and quantify inertial cavitation in order to induce drug release from liposomes. In this purpose, an inertial cavitation dose (CD), based on broadband noise emission associated with inertial cavitation, was defined to monitor in vitro encapsulated drug release. The CD was chemically validated with the dosing of hydroxyl radicals generated by bubbles collapses under various pulsed ultrasound exposures. A high correlation between doxorubicin (dox) release rate from liposomes and CD was de monstrated for all liposomes formulations tested and under different pulsed ultrasound exposures. The role of temperature on hydroxyl radical production and dox release was also investigated. The performed experiments allowed selecting the liposomes formulations that are the most sensible to ultrasound in order to test them on rats implanted with prostatic tumors. After several campaigns of in vivo experiments performed with various ultrasonic setups and liposomes formulations, the benefit of the combined treatment was demonstrated.

Ce travail de recherche est dédié à la compréhension des mécanismes physiques de l’érosion de cavitation dans un fluide compressible à l’échelle fondamentale de l’implosion d’une bulle de cavitation. Suite à l’implosion d’une bulle de vapeur à proximité d’une surface solide, des très hautes pressions sont générées. Ces pressions sont considérées responsables de l’endommagement (érosion) des surfaces solides observé dans la plupart des applications. Notre approche numérique démarre avec le développement d’un solveur compressible capable de résoudre les bulles de cavitation au sein du code volumes finis YALES2 en utilisant un simple modèle de mélange homogène des phases fluides. Le solveur est étendu à une approche ALE (Arbitraire Lagrangien Eulérien) dans le but de mener des simulations d’interaction fluide-structure sur un maillage mobile. La réponse du matériau solide est calculée avec le code de calcul éléments finis Cast3M, et nous a permis de mener des simulation avec un couplage d’abord monodirectionnel, ensuite bidirectionnel, entre le fluide et le solide. On compare des résultats obtenus à deux dimensions, puis à trois, avec des observations expérimentales. On discute les chargements de pression estimés, et les réponses de différents matériaux pour des implosions de bulle à des différentes distances de la surface. Enfin, à travers l’utilisation de simulations avec couplage bidirectionnel entre fluide et solide, on identifie l’amortissement des chargements de pression pour les différents matériaux. / This research is devoted to understanding the physical mechanism of cavitation erosion in compressible liquid flows on the fundamental scale of cavitation bubble collapse. As a consequence of collapsing bubbles near solid wall, high pressure impact loads are generated. These pressure loads are believed to be responsible for the erosive damages on solid surface observed in most applications. Our numerical approach begins with the development of a compressible solver capable of resolving the cavitation bubbles in the finite-volume solver YALES2 employing a simplified homogenous mixture model. The solver is extended to Arbitrary Lagrangian-Eulerian formulation to perform fluid structure interaction simulation with moving mesh capabilities. The material response is resolved with the finite element solver Cast3M, which allowed us to perform one-way and two-way coupled simulations between the fluid and solid domains. In the end, we draw comparisons between 2D and 3D vapor bubble collapse dynamics and compare them with experimental observations. The estimated pressure loads on the solid wall and different responses of materials for attached and detached bubble collapses are discussed. Finally, the damping of pressure loads by different materials is identified with two-way coupled fluid-structure interaction.

Student Number : 9910049F - MSc (Eng) dissertation - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built Environment / Cavitation was generated in tap water samples by the transmission of tension waves into the liquid, using a hydrodynamic shock tube. The liquid cavitated at absolute negative pressures of about -1 bar. Simulations of bubble responses showed qualitative agreement with experimental observations of oscillatory growth and collapse cycles. Pressure records showed secondary pressure pulsations, confirming the oscillatory nature of the collapse at each rise in pressure. More quantitative comparison of theory and photographic records would require a camera with a higher capture rate. Experiments using another experimental facility involved liquid compression waves with peak static pressures of up to about 1 MPa, which were transmitted from a conventional gas shock tube into a liquid section and were intended to be reflected at the free surface as expansion waves. These experiments were unsuccessful in producing absolute negative pressures or cavitation that was visible through an optical observation section. This was attributed to transition layer effects and pulse attenuation, which contributed to lowering of the peak negative pressure behind the expansion wave, as well as the depth of the transducer and observation section below the free surface, which may have been too low for the peak tension to be superimposed on the lower pressure behind the incident compression wave. Pressure records suggested that, for lower driver pressures, cavitation occurred below the observation section, although this could not be verified optically.

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.

<p>The valve plate/cylinder block interface in an axial piston pump is often subject to extreme pressures, which can cause wear of the valve plate and ultimately, failure of the pump. The purposes of this study were to: a) experimentally investigate the film thickness generated between a floating valve plate and cylinder block in situ using proximity probes, b) develop a model which can predict the motion, film thickness and pressures of the floating valve plate and corroborate with experimental results, c) investigate surface pockets to provide additional lubricant at the valve plate interface by measuring the flow velocities and cavitation areas in a thrust washer bearing, d) numerically investigate surface modifications of the floating valve plate to observe any changes in lubricant pressure, temperature, cavitation, or valve plate deformation. Two different test rigs were designed, developed and used to investigate the performance of axial piston pumps and surface pockets. The axial piston pump test rig (APTR) was designed to operate and measure the steady state conditions of an axial piston pump. The APTR utilizes three non-contact proximity probes to measure the valve plate motion and film thickness between the cylinder block at various speeds and pressures. A thrust washer test rig (TWTR) was developed to measure the cavitation areas and flow velocities of lubricant in a pocketed thrust washer using μPIV. Through a novel interpolation approach, the depths of the micro-particles in the bearing pocket were determined using an analytical model. Using this approach, the μPIV measured 2D velocity field was employed to develop a 3D velocity field, which illustrates the fluid motion inside a pocketed thrust bearing at various speeds and viscosities. A dynamic lubrication model was developed using the thermal Reynolds equation augmented with the JFO boundary condition and the energy equation to determine the pressure, cavitation regions and temperature of the lubricant at the valve plate cylinder block interface. The lubricating pressures were then coupled with the equations of motion of the floating valve plate to develop a dynamic lubrication model. The stiffness and damping coefficients of the floating valve plate system used in the dynamic lubrication model were determined using a parametric study. The elastic deformation of the valve plate was also considered using the influence coefficient matrix approach. The experimental and analytical motion of the valve plate were then corroborated and found to be in good agreement. 4 and 8 pocket designs were then added as surface modifications to the floating valve plate in the dynamic lubrication model. The addition of surface modifications improved the lubricating conditions at the valve plate/cylinder block interface and resulted in increased minimum film thicknesses and lowered lubricant temperatures at the same operating conditions.</p>

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / M.S.

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.

A sharp interface cavitation model has been developed for computational fluid dynamics. A phase change model based on a simplification of the Rayleigh-Plesset equation is combined with a second-order volume-of-fluid method with a constructed level set function in an incompressible fluid dynamics model. The semi-implicit phase change model predicts the mass flux between liquid and vapor phases based on the difference between the local pressure at the interface and the vapor pressure at the ambient conditions. The mass flux between phases determines the volume source strength and jump velocities at the interface. To prevent difficulties computing derivatives near the interface, two separate velocity fields from the momentum equation are solved considering the interface velocity jump. The interface velocity jump is extended into the liquid and vapor domains using a fast marching method. A description of the mathematical and numerical models is included, as well as an explanation and derivation of the phase change model. Hypothetical vapor bubble problems are demonstrated to test the components of the model. Finally, cavity evolution on a hydrofoil is computed for a range of parameters.