Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The phenomenon of cavitation on the metal surface causes erosion decaying components in operation, in particular the blades of turbines for power generation, accounting for maintenance costs and losses in electricity generation resulting from periodic stops. The blades of these turbines, particularly those manufactured by C-Mn steel (carbon - manganese) are coated by arc welding for stainless steel protective order to present more uptime or longer intervals between maintenance periods. Among the materials used to coat these blades are austenitic stainless steels, and stainless steels featured in the Co and Cobased alloys (commercially Stellites). However, the latter have a high cost. Among the welding processes applied to the coating, the technique of adding cold wire (GMAW and GMAW-CW-AF) is presented as an advantageous tender in relation to other techniques currently existing special and conventional welding. Given the context, this work seeks to study, apply and evaluate the effect of alloy and austenitic stainless steel alloys Co (CoCrMo and CoCrW) deposited by GMAW-CW for the purpose of characterization, comparison, formulation and deposition of new alloys from commercial wire correlating with resistance to mass loss. The adjustments of welding technique have focused on obtaining the manufacture of coatings suitable welding parameters. The cavitation wear resistance was evaluated according to ASTM G 32, correlating microstructure and phases by optical microscopy, SEM-EDS, chemical composition and optical emission spectrometry analyzes of the phases present by XRD. The qualities of the welded surfaces have been analyzed by visual examination and Penetrant Liguid according to standard NT (Nondestructive Testing). It was found that the coatings showed good weldability without discontinuities or defects with good surface finish. In the analysis of the coatings of cobalt, the alloy H (Stellite electrode 21 and 309LSi as cold wire) and M (Stellite 6 and 309LSi electrode as cold wire) showed good performance in resistance to cavitation in similar levels of surface roughness and hardness when compared to coatings Stellites 21 and 06, made by conventional GMAW process. / O fenômeno da cavitação sobre a superfície metálica provoca à erosão que deteriora componentes em operação, em particular as pás de turbinas hidráulicas de geração de energia, sendo responsável por custos da manutenção e perdas em geração de energia elétrica decorrente das paradas periódicas. As pás dessas turbinas, em especial as fabricadas pelo aço C-Mn (carbono manganês) são revestidas por soldagem a arco por aços inoxidáveis a fim de proteção para que apresentem maior tempo de operação ou maior intervalo entre os períodos de manutenção. Entre os materiais aplicados para revestir essas pás estão os aços inoxidáveis austeníticos, e em destaque os aços inoxidáveis ao Co e as ligas à base de Co (comercialmente Stellites). No entanto, estes últimos apresentam alto custo. Entre os processos de soldagem aplicados para o revestimento, a técnica de adição de arame frio (GMAW-CW ou GMAW-AF) se apresenta como uma proposta vantajosa em relação às outras técnicas especiais de soldagem existentes atualmente e convencionais. Diante do contexto, este trabalho buscou estudar, aplicar e avaliar o efeito das ligas de aço inoxidáveis austeniticos e ligas de Co (CoCrMo e CoCrW) depositadas pelo processo GMAW-CW com a finalidade de caracterização, comparação, formulação e deposição de novas ligas a partir de arame comerciais, relacionando com a resistência à perda de massa. As adequações da técnica de soldagem têm como foco a obtenção dos parâmetros de soldagem adequados à confecção dos revestimentos. A resistência ao desgaste por cavitação foi avaliada segundo a Norma ASTM G 32, correlacionando com a microestrutura e fases por microscopia óptica, MEV-EDS, composição química por espectrometria de emissão óptica e análises das fases presentes por DRX. As qualidades das superfícies soldadas foram analisadas por análise visual e Líquido Penetrante de acordo com a norma de END (Ensaio Não Destrutivo). Verificou-se que os revestimentos apresentaram boa soldabilidade, sem descontinuidades ou defeitos, com bom acabamento superficial. Na análise dos revestimentos de cobalto, as ligas H (eletrodo Stellite 21 e 309LSi como arame frio) e M (eletrodo Stellite 6 e 309LSi como arame frio) apresentaram bom desempenho de resistência a cavitação em semelhantes níveis de rugosidade e dureza quando comparados aos revestimentos de Stellites 21 e 6, feitos pelo processo GMAW convencional. / Doutor em Engenharia Mecânica

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, where it was possible to see the potential of applying this new model of reactor, especially due to the low operating costs and practicality of operation.

A sonotrombólise pela combinação de ultrassom (US) e microbolhas com medicamento trombolítico tem indicado grande eficácia na quebra de coágulos in vitro, devido a efeitos de cavitação. Contudo, estudos in vivo sobre drug delivery demonstram que a cavitação de microbolhas é também capaz de abrir local e transientemente a barreira hematoencefálica (BHE) - estrutura de permeabilidade seletiva que protege o Sistema Nervoso Central. Um estudo clínico sobre sonotrombólise foi interrompido precocemente devido a evolução de casos de Acidente Vascular Cerebral isquêmicos para hemorrágicos associados a danos na BHE e formação de ondas estacionárias. Nesta tese, foram realizados estudos in vitro e in vivo sobre técnicas de US multifrequencial para trombólise. Além disso, verificou-se os limiares para a abertura da BHE e efeitos de neuromodulação ambos causados pelo ultrassom transcraniano. Foi demonstrado que o duplo feixe de US e a variação temporal de frequências (excitação codificada) são capazes de reduzir a formação de ondas estacionárias e gerar regiões focais mais confinadas do que feixes focalizados monofrequenciais. O duplo feixe foi incapaz de gerar ondas de baixa frequência para trombólise (menor ou igual a 1 Pa para feixes primários de 1,58 MPa). Exames histológicos e por imagens de ressonância magnética mostraram que a cavitação de microbolhas pode causar danos ao tecido cerebral para níveis de pressão de mesma ordem necessários para se observar efeito trombolítico. Além disso, foi observado que o US é capaz de disparar atividade neuronal causando respostas motoras e indícios de respostas associadas a modulação de atividades cognitivas. A focalização de feixes por excitação multifrequencial é um grande avanço para sonotrombólise. Contudo, a potencialização do efeito trombolítico do US por cavitação e medicamento é limitada devido a danos a BHE e critérios de exclusão do medicamento. / Sonothrombolysis by combining ultrasound (US) and microbubbles with thrombolytic drugs has been demonstrated capable of breaking blood clots in in vitro studies, due to cavitation effects. However, in vivo drug delivery studies have demonstrated that cavitation of microbubbles is also capable of opening locally and transiently the blood-brain barrier (BBB) - structure with selective permeability that protects the Central Nervous System. A sonothrombolysis clinical study was interrupted prematurely because of the occurrence of intracerebral hemorrhages after treatment associated with damages in the BBB and standing waves formation. In this dissertation, in vitro and in vivo studies evaluated techniques of multifrequency US for thrombolysis. Furthermore, the ultrasound pressure threshold to obtain the BBB opening and neuromodulation effects were explored during transcranial insonation. It has been demonstrated that the double US beam and the time variation of frequencies (coded excitation) are capable of reducing standing wave formation and generating more confined focus zones than monofrequency focused beams. The double US beam was not capable of generating low frequency waves for thrombolysis (less than or equal to 1 Pa obtained from primary beams with 1.58 MPa). Histological exams and magnetic resonance images demonstrated that microbubbles cavitation can damage the brain tissue with acoustic pressures of the same level necessary to observe thrombolytic effects. Furthermore, it was observed motor responses and other responses associated with cognitive activity triggered by US. The capability of multifrequency excitation in focusing US beams is an important advance for sonothrombolysis. However, the enhancement of fibrinolytic effect of US by microbubbles cavitation and with thrombolytic drugs is limited by associated damages to the BBB and by exclusion criteria for the use of the thrombolytic drugs.

O presente trabalho reúne elementos teóricos e experimentais envolvendo os principais fenômenos hidráulicos causadores de danos em bombas hidráulicas de fluxo radial de grande porte. A preocupação do texto está centrada em proporcionar um aprofundamento técnico acerca destes fenômenos hidráulicos de cavitação, a fim de contribuir na análise e solução de problemas em sistemas de bombeamento. Além disso, este trabalho tem a pretensão de transmitir alguma experiência prática fornecida por um evento em que foi detectada a ocorrência de dois destes fenômenos hidráulicos simultâneos em um sistema de bombeamento e a partir disso, realizou-se a análise completa deste evento, incluindo as propostas de solução aos problemas encontrados, as análises técnica e econômica das alternativas de solução e a análise após a implantação da proposta escolhida. O texto apresenta também uma grande quantidade de gráficos e figuras que buscam facilitar a compreensão das definições e das análises dos fenômenos hidráulicos, além de exemplificar os danos típicos dos fenômenos pela visualização direta destes danos nas bombas. / This work presents theoretical and experimental data on the principal hydraulic phenomena responsible for damage in high loaded radial flow hydraulic pumps. The main objective is to provide a technical overview in order to contribute for the analysis and solution on these cavitation pumping systems problems. In addition this work intends to transmit practical experience through a “study of case” where two simultaneous of these hydraulic phenomena were detected. The complete analysis of technical and economical aspects of the alternatives solutions is presented including a great amount of graphs and illustrations that better explain the phenomena of cavitation in hydraulic pumps.

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, a amostra do aço nitretado, com nitrogênio em solução sólida e solubilizado (318HTGN+Sol), e as laminadas (318HTGN+Enc), apresentaram taxa de desgaste 2 e 17 vezes menores, respectivamente, comparadas com o aço AISI 304L encruado. Foi possível constatar um aumento considerável do tempo de incubação, o que permitiu, de forma detalhada, acompanhar os mecanismos de deformação e evidenciar nos primeiros estágios da cavitação a formação de bandas de escorregamento. Foi possível, também, observar como os contornos de grão ou de macla, locais preferenciais de nucleação do dano, atuam quando comparados com danos no interior dos grãos. / This work aims to establish relationships between micro and nanostructure and cavitation-erosion resistance in high nitrogen stainless steels. These relations will be determined through the study of plastic deformation mechanisms and surface damage, as well as micro and nanostructure during vibratory cavitation testing. An UNS S 31803 samples with 0.9 N (%wt) were obtained by high temperature gas nitriding. Two sample groups were obtained: solubilized in solid solution and solubilized and work hardened. Vibratory cavitation tests were performed in distilled water. The damage mechanisms operating in different stages of wear were analyzed for different times in the same location using scanning electron microscopy (SEM). Mass losses were periodically measured during the cavitation-erosion tests. From the results, it was observed that the (318HTGN+Sol) samples, with nitrogen in solid solution showed wear rates 16.1 times smaller compared to those of the solubilized UNS S30403 steel. The work-hardened (318HTGN+Enc) samples showed wear rates 172.4 times smaller than UNS S30403specimens. The comparison of the 318HTGN+Sol samples with the work-hardened 304L+Enc specimens showed wear rates 2 times smaller, while the 318HTGN+Enc samples showed a wear rate 17 times smaller. Finally, a considerable increase of incubation time was readily observed, which allowed the detailed observation of the deformation mechanisms and the identification of the slip bands formation during the early stages of cavitation erosion. Additionally it was possible to observe the way the grain boundaries and twin boundaries are damaged, acting as preferential sites where the damage initially occurs.

A presente dissertação investiga o comportamento do escoamento em um túnel de cavitação, através de simulações fluido-dinâmicas computacionais, excluindo a bomba de circulação. Para tanto um extenso estudo buscou selecionar a abordagem numérica e configurações de simulação mais adequadas, de uma forma a reproduzir as características hidrodinâmica inerentes à operação do túnel. Portanto, as informações referentes à perda de carga, uniformidade no perfil de velocidade, tendência de cavitação, descolamento e altura da camada limite foram apreciadas. Esse estudo foi direcionado por dados provenientes de métodos empíricos da literatura, resultados experimentais do próprio túnel pesquisado e de outros túneis. Em geral, os resultados foram satisfatórios, pois a perda de carga estimada foi semelhante ao obtido experimentalmente. Além de serem identificados os trechos com efeito desfavorável na uniformidade do escoamento, foram determinadas a distribuição de pressão nas aletas e o perfil de velocidade incidente na bomba. / This study deals with a cavitation tunnel flow (except the pump region) through computational fluid dynamic simulations. Therefore, previously one made a literature survey to aid the selection of the most appropriate techniques and simulation settings to simulate the hydrodynamic characteristics of the tunnel. The pressure drop, uniformity of the velocity profile, existence of cavitation, detachment and height of the boundary layer were evaluated. This study used empirical methods and also experimental results. The results were satisfactory, as long as the estimated pressure drop was close to the one obtained experimentally. In addition, it was forecasted low flow uniformity in some parts of the tunnel, the pressure distribution on the fins and the incident velocity profile at the pump.

Les caoutchoucs naturels chargés sont largement utilisés pour leurs excellentes propriétés mécaniques comme matériaux structurels dans les pneumatiques. Leurs excellentes performances sont souvent associées à leur capacité à cristalliser sous tension. Dans le cas de la fatigue cyclique, la dissipation induite par la création et fusion de cristallites est souvent donnée comme responsable de la bonne résistance des caoutchoucs naturel à la propagation de fissures. Ce travail de doctorat s'est focalisé sur les divers mécanismes dissipatifs qui sont activé par les grandes déformations rencontrées près d'une pointe de fissure. La diffusion des rayons X a été utilisée pour caractériser les changements de structure à des échelles sub-microniques, tels que la cristallisation sous tension, la création de nano-cavités, ou la réorganisation de la charge. Un premier volet de l'étude s'est focalisé sur des tests uniaxiaux, afin d'étudier l'effet d'un changement de formulation du matériau (taux de charge, densité de réticulation), d'un vieillissement thermique, ou encore d'une élévation de la température sur ces modification de structure. Dans une seconde partie, une caractérisation complète de fissures de fatigue a été effectuée. La corrélation d'image numérique a été utilisée pour mesurer les déformations locales au voisinage d'une pointe de fissure, et les rayons X ont permis d'y associer une mesure locale de la structure du matériau. Les propriétés de fatigue de ces matériaux ont été mit en regard des structures observées afin de discuter leur relation. Il a été mis en évidence que le rôle de la cristallisation dépassait largement sa contribution à la dissipation locale. / Filled natural rubbers are widely used in structural parts such as tires for their outstanding mechanical properties. Their exceptional behavior is often associated to the ability of natural rubber chains to form a crystalline structure under tension. In the case of cyclic fatigue cracking, the dissipation added through crystallization and melting at the crack tip is often seen as the main reinforcing mechanism that reduces fatigue crack growth. This PhD work focused on all the dissipative mechanisms activated by the strain amplification near a crack tip. An extensive use of X-ray scattering was made to investigate sub-micronic changes in structure (strain-induced crystallization, cavitation, filler network). A study was made in uniaxial tension to understand the effects of material composition and test environment on these structure changes. The effect of filler volume fraction, crosslink density, thermal ageing and test temperature were considered. This study was followed by a complete description of several fatigue crack-tips. Digital image correlation was used to map the strain fields at the vicinity of the cracks, while X-ray mapping of the process zone gave information on the local changes in structure. The cyclic fatigue properties of the materials were then discussed through the knowledge acquired both in uniaxial tension and near crack-tips. It showed that the effect of strain induced-crystallization far outweigh the dissipation added.

Par ce travail, nous avons voulu mieux cerner les paramètres cinématiques d’une manipulation cervicale, mais également les confronter au ressenti subjectif des sujets qui en ont bénéficié.Pour situer le contexte, nous avons débuté en relatant les données de la littérature quant à la définition, aux indications, à l’efficacité, aux risques, à la cinématique des manipulations vertébrales et à la place de cette technique dans le modèle bio-psycho-social des soins de santé.Nous avons réalisé un ensemble d’études aux Laboratoires d’Anatomie, de Biomécanique et d’Organogénèse (LABO) et d’Anatomie Fonctionnelle (LAF) de l’ULB. Elles portaient, d’une part, sur l’évaluation de la cinématique de la manipulation cervicale et ses répercussions sur le ressenti subjectif des individus en bénéficiant et, d’autre part, sur l’étude de l’axe hélicoïdal au moment de l’impulsion ainsi que l’analyse des effets de la manipulation sur l’amplitude active et l’erreur de repositionnement céphalique d’individus asymptomatiques.Au vu de nos résultats et de ceux de la littérature, une influence majeure du type de technique sur les paramètres cinématiques de la manipulation cervicale existe.Nous avons pu mettre en évidence que les amplitudes, vitesses et accélérations utilisées lors des manipulations cervicales HVBA sont liées à la technique évaluée et dépendent largement du praticien et de son expérience.De manière générale, nos résultats étaient en accord avec la littérature, avec des amplitudes de rotation axiale faibles. Ces résultats peuvent être liés au fait que certains praticiens étaient familiarisés à l’usage de la technique à composantes multiples.Notre évaluation de l’expérience subjective des individus a fait ressortir deux dimensions que nous avons appelées :facteur 1 et facteur 2. Le premier traduirait l’aspect technique de la manipulation, le second celui, plus personnel, de ressenti du relâchement.Il existe des liens clairs entre l’expérience subjective des individus (ESI) et les paramètres cinématiques de la manipulation. Il en va de même entre l’ESI et la présence d’une cavitation. Les manipulations avec cavitation étaient ressenties comme plus amples, plus rapides et réalisées à l’aide d’une prise plus ferme ainsi qu’une manœuvre plus précise.Les praticiens jouissant d’une plus longue expérience ont obtenu de meilleurs scores pour les items en relation avec les aspects techniques de la manipulation.Le recours à l’axe hélicoïdal a démontré un intérêt indéniable dans l’analyse de la cinématique de la phase d’impulsion de la manipulation cervicale et son orientation a fait preuve d’une grande variabilité selon les individus manipulés.La mobilité active de nos sujets asymptomatiques n’a pas été modifiée suite aux manipulations pratiquées.La poursuite de la recherche d’une meilleure compréhension de la manipulation cervicale HVBA, la connaissance et la reconnaissance des facteurs de risque et contrindications, associées à un enseignement de qualité et une pratique régulière (quotidienne) sont, à notre avis, les garants d’un usage optimal de cet outil thérapeutique. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

To increase profitability for biogas production, new innovative substrates and condition of operations needs to be implemented. At the current state, fats, oils and greases (FOGs) represent a promising substrate even though it brings operational challenges to the anaerobic digestion process. By utilizing hydrodynamic cavitation (HC) as a pre-treatment of the FOGs, the efficiency of FOGs’ co-digestion with wastewater sludge can be significantly improved. Preliminary experiments conducted on oil and water demonstrates that the HC pre-treatment improves the oil solubilisation as well as forms stable oil and water emulsion that last for several hours. The pre-treatment also improved the soluble chemical oxygen demand (COD) of biosludge (BiSl) by up to 115% and the initial degradation rate by up to 35%. In a semi-continues system, this allowed a significant increment in the specific methane yield depending on the organic loading rate (OLR) applied1. With sufficient process optimization, the HC-pre-treatment may prove to be an energy efficient and effective pre-treatment of FOGs.

We consider mathematical modeling of thin film flow between two rough surfaces which are in relative motion. For example such flows take place in different kinds of bearings and gears when a lubricant is used to reduce friction and wear between the surfaces. The mathematical foundations of lubrication theory is given by the Navier--Stokes equation, which describes the motion of viscous fluids. In thin domains several approximations are possible which lead to the so called Reynolds equation. This equation is crucial to describe the pressure in the lubricant film. When the pressure is found it is possible to predict vorous important physical quantities such as friction (stresses on the bounding surfaces), load carrying capacity and velocity field. In hydrodynamic lubrication the effect of surface roughness is not negligible, because in practical situations the amplitude of the surface roughness are of the same order as the film thickness. Moreover, a perfectly smooth surface does not exist in reality due to imperfections in the manufacturing process. Therefore, any realistic lubrication model should account for the effects of surface roughness. This implies that the mathematical modeling leads to partial differential equations with coefficients that will oscillate rapidly in space and time. A direct numerical computation is therefore very difficult, since an extremely dense mesh is needed to resolve the oscillations due to the surface roughness. A natural approach is to do some type of averaging. In this PhD thesis we use and develop modern homogenization theory to be able to handle the questions above. Especially, we use, develop and apply the method based on the multiple scale expansions and two-scale convergence. The thesis is based on five papers (A-E), with an appendix to paper A, and an extensive introduction, which puts these publications in a larger context. In Paper A the connection between the Stokes equation and the Reynolds equation is investigated. More precisely, the asymptotic behavior as both the film thickness <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cepsilon" /> and wavelength <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmu" /> of the roughness tend to zero is analyzed and described. Three different limit equations are derived. Time-dependent equations of Reynolds type are obtained in all three cases (Stokes roughness, Reynolds roughness and high frequency roughness regime). In paper C we extend the work done in Paper A where we compare the roughness regimes by numeric computations for the stationary case. In paper B we present a mathematical model that takes into account cavitation, surfaces roughness and compressibility of the fluid. We compute the homogenized coefficients in the case of unidirectional roughness.In the paper D we derive a mathematical model of thin film flow between two close rough surfaces, which takes into account cavitation, surface roughness and pressure dependent density. Moreover, we use two-scale convergence to homogenize the model. Finally, in paper E we prove the existence of solutions to a frequently used mathematical model of thin film flow, which takes cavitation into account.