Military aircraft that require high maneuverability, durability, ballistic protection, reparability, and energy efficiency require structural alloys with low density, high toughness, and high strength. Also, repairs to these aircraft demand a production process that has the flexibility to be relatively in-situ with the same high-performance output. Materials produced by the cold spray process, a thermo-mechanical powder consolidation technique, meet many of the requirements. In accordance with President Obama’s 2011 Materials Genome Initiative, the focus of this effort is to design customized aluminum alloy powders which exploit the unique behavior and properties of the materials created by the cold spray process. Analytical and computational models are used to customize microchemistry, thermal conditioning, and solidification behavior of the powders by predicting equilibrium and non-equilibrium microstructure and resulting materials properties and performance. Thermodynamic, kinetic, and solidification models are used, including commercial software packages Thermo-Calc, Pandat™, and JMatPro®, and TC-PRISMA. Predicted powder properties can be used as input into a cold spray process impact model to determine the consolidated materials’ properties. Mechanical properties of powder particles are predicted as a function of powder particle diameter and are compared to experimental results.

Submitted by Maicon Juliano Schmidt (maicons) on 2015-07-13T19:17:40Z No. of bitstreams: 1 Eduardo Schnurr Siqueira.pdf: 1543388 bytes, checksum: 203a2765367b043538126c29889d7be5 (MD5) / Made available in DSpace on 2015-07-13T19:17:40Z (GMT). No. of bitstreams: 1 Eduardo Schnurr Siqueira.pdf: 1543388 bytes, checksum: 203a2765367b043538126c29889d7be5 (MD5) Previous issue date: 2013-01-31 / Nenhuma / Fluidos não-Newtonianos apresentam relação não linear entre a tensão de cisalhamento e a taxa de cisalhamento, ou seja, sua viscosidade não é constante. Eles estão presentes na natureza (sangue, lamas, areia movediça), assim como em muitos produtos industriais classificam-se nesta categoria, tais como produtos alimentícios (iogurtes, queijos cremosos, doces de frutas, chocolate ), tintas, borrachas, polímeros fundidos, soluções poliméricas, adesivos e gomas. Nos casos em que a viscosidade diminui com aumento da taxa de cisalhamento, os fluidos são classificados como pseudoplásticos; os que apresentam comportamento inverso são classificados como dilatantes. O modelo Power-Law é utilizado em engenharia para modelar ambos os comportamentos. Computational Fluid Dynamics - CFD (Dinâmica dos Fluidos Computacional) é uma ferramenta utilizada na simulação numérica de escoamentos de fluidos Newtonianos e não-Newtonianos. Inúmeros códigos comerciais e livres são utilizados atualmente, dentre eles o código livre e aberto Multiphase Flow with Interphase Exchanges (MFIX), o qual foi desenvolvido visando a simulação numérica de escoamentos multifásicos reativos do tipo sólido-gás em leitos fluidizados. O objetivo do presente trabalho é implementar no MFIX o modelo Power-Law, validar a modificação e realizar um estudo de caso utilizando o modelo. Com a implementação de um modelo não-Newtoniano ao código, pretende-se abrir caminho para a simulação de escoamentos multifásicos do tipo sólido-líquido não-Newtoniano, bem como aumentar a potencialidade do código, a fim de se estudar casos monofásicos de escoamentos de fluidos não-Newtonianos sujeitos à transferência de calor. O modelo implementado foi validado através da comparação com resultados da literatura para o escoamento em uma cavidade. Posteriormente, foram realizadas simulações do escoamento não isotérmico e isotérmico em torno de um prisma de seção quadrada imerso em um canal. Foram variados os parâmetros número de Prandtl, índice do modelo Power-Law e razão de bloqueio. Verificou-se que o número de Nusselt tem influência direta e é fortemente influenciado pela razão de bloqueio e inversamente, com pouca intensidade, pelo índice Power-Law. O número de Prandtl também influenciou diretamente no número de Nusselt e demonstrou que, quanto maior o seu valor, mais acentuada fica a variação do número de Nusselt em função da razão de bloqueio. / Non-Newtonian fluids exhibit nonlinear relationship between the shear stress and the shear rate, that is, its viscosity is not constant. They are present in nature (blood, sludge) as well as many industrial products are classified in this category, such as food products (yoghurt, soft cheeses, jams, chocolate), paints, rubber, polymer melts, polymer solutions, adhesives and gums. In cases where viscosity decreases with increasing shear rate, the fluids are classified as shear-thinning, while the opposite behavior is classified as shear-thickening. The Power-Law model is used in engineering to model both behaviors. Computational Fluid Dynamics - CFD is a tool used in the numerical simulation of Newtonian and non-Newtonian fluid flow. Numerous free and commercial codes are used today, including the free and open source Multiphase Flow with Interphase Exchanges (MFIX), which was developed to the numerical simulation of multiphase (fluid-solid) and reactive flows. The goal of this work is to implement the Power-Law model in MFIX, validate the implementation and conduct a case study using the model implemented. With the implementation of a non-Newtonian model to the code, a new possibility for the simulation of multiphase flows of solid-non-Newtonian liquids is opened, as well as there is an increase in the capability of the code regarding the study of single-phase fluid flows of Non-Newtonian fluids subject to heat transfer. The model was implemented and validated by comparison with literature results for the flow in a lid driven cavity. Subsequently, simulations were carried out concerning isothermal and non-isothermal flows around a square cylinder immersed in a channel. Parameters of analyses consisted of Prandtl number, Power-Law index and blockage ratio, for a fixed Reynolds number. It was found that the Nusselt number is strongly influenced by the blockage ratio and decreases with the increase of the Power-Law index. The Prandtl number also directly influences the process. With its increase, the dependence of the Nusselt number with the blockage ratio is more pronounced.

Cette thèse expérimentale et numérique s’intéresse à l’écoulement à inertie négligeable d’un fluide newtonien et d’un fluide à seuil autour d’une plaque ou d’un cylindre en présence d’une paroi. Les efforts générés et les structures d’écoulement ont été particulièrement étudiés. Pour le fluide à seuil, l’étude est centrée sur le domaine des effets de seuil grands par rapport aux effets visqueux. Pour l’approche expérimentale, un dispositif a été conçu permettant de mesurer simultanément les forces de traînée et de portance en fonction de la vitesse et de la distance obstacle/paroi. Les fluides étudiés sont un sirop de glucose Newtonien et un gel de Carbopol considéré comme un fluide à seuil modèle. Ces matériaux ont été finement caractérisés du point de vue rhéologique. Des simulations numériques utilisant le modèle viscoplastique anélastique d’Herschel-Bulkley régularisé par le modèle de Papanastasiou ont été réalisées. Les résultats obtenus avec le fluide newtonien ont permis de valider l’installation expérimentale et l’approche numérique. Les effets de la contrainte seuil, de la distance paroi/obstacle, de la rhéofluidification, de l’angle d’inclinaison de la plaque sur les coefficients de traînée et de portance ont été examinés en détail. Le régime de lubrification a été étudié pour le cylindre expérimentalement et théoriquement. La morphologie de l’écoulement (zones rigides) et les grandeurs locales ont été montrées. Des solutions analytiques de la traînée et de la portance ont été proposées. Les comparaisons entre les résultats expérimentaux et numériques ainsi qu’avec les solutions issues de la plasticité de la mécanique des sols sont analysées. Les écarts sont discutés en termes d’influence de l’élasticité et de plasticité du fluide à seuil. / This experimental and numerical thesis deals with the creeping flow of a Newtonian fluid and a yield stress fluid around a plate or a cylinder in the presence of a wall. The generated forces and the flow structures have been particularly studied. The study focuses for the yield stress fluid on large yield stress effects compared to the viscous effects. For the experimental approach, a device has been designed to measure simultaneously the drag and lift forces as a function of velocity and obstacle / wall distance. The fluids studied are a Newtonian glucose syrup and a Carbopol gel considered as a yield stress fluid model. These materials have been finely characterized from the rheological point of view. Numerical simulations using the Herschel-Bulkley anelastic viscoplastic model regularized by the Papanastasiou model were carried out. The results obtained with the Newtonian fluid allowed to validate the experimental set-up and the numerical approach. The effects of the yield stress, the wall / obstacle distance, the power law index and the inclined plate on the drag and lift coefficients were carefully examined. The lubrication regime has been studied for the cylinder both experimentally and theoretically. The morphology of the flow (rigid zones) and the local field quantities have been shown. Analytical solutions of drag and lift have been proposed. Comparisons between the experimental and numerical results as well as the solutions resulting from the plasticity of soil mechanics are analyzed. Deviations are discussed in terms of the elasticity and plasticity influence of the yield stress fluid.

Explicações científicas são um dos elementos mais importantes do ensino de ciências. Elas estão relacionadas com a noção de natureza de ciência que reproduzimos, à compreensão adequada de conceitos e ao compartilhamento de hipóteses e princípios científicos. Embora não haja uma definição única de explicação científica que seja aceita de forma consensual por parte dos pesquisadores desse tema, nas últimas décadas ele tem sido abordado em um número crescente de trabalhos publicados em periódicos internacionais especializados em pesquisas sobre Ensino de Ciências. Apesar disso, consideramos que este tema tem recebido pouca atenção da comunidade de pesquisa em ensino de Ciências no Brasil, em particular no que diz respeito a atividades relacionadas à construção de explicações científicas durante a formação de professores. Neste trabalho investigamos elementos que fazem parte de explicações produzidas por futuros professores e a forma como estes elementos são relacionados entre si na organização da explicação. Para isso, propomos uma forma de estrutura organizacional de explicações científicas e a utilizamos para analisar seminários apresentados por alunos de um curso de licenciatura em Física durante uma das disciplinas deste curso, referente a tópicos relacionados ao conteúdo de mecânica. Nossa estrutura organizacional foi elaborada a partir de trabalhos realizados por James Wertsch (2008) sobre narrativas, a partir dos quais adaptamos para o estudo de explicações científicas duas estruturas que Wertsch propôs com respeito a narrativas: explicações específicas e moldes esquemáticos explicativos. Relacionamos as explicações específicas aos momentos explicativos propostos por Ogborn, Kress, Martins e Mcgillicuddy (1996) e os moldes esquemáticos explicativos a tipos de explicações propostos por filósofos das explicações – em particular o modelo Mecânico-Causal, as explicações de Unificação e explicações Funcionais. Em nossa análise empírica buscamos identificar objetivos pedagógicos que os diferentes tipos de explicações científicas identificadas se destinaram a atender e observamos uma (inesperada) baixa ocorrência de explicações científicas nos seminários que acompanhamos, acompanhada de uma forte ênfase no treinamento da habilidade de resolução de problemas matemáticos. Utilizamos estes resultados para problematizar questões relacionadas à formação de professores para a educação básica à luz do uso que é feito de explicações científicas. / Scientific explanations are among the most important elements in science teaching. They relate to the notion of nature of science we reproduce, to the better understanding of concepts and to share scientific principles and hypotheses. Although there is no single scientific explanation's definition consensually accept by researchers in this theme, in the last decades it has been addressed in an increasing number of papers published in international journals on science teaching. However, we believe that this issue has received little attention from the research community in science teaching in Brazil, specially about activities related to constructing scientific explanations during teacher training. In this work we investigate elements related to scientific explanations elaborated by future teachers, and the way those elements are related to each others in explanation organization. For this, we propose an organizational structure of scientific explanation and we use it to analyze seminars presented by students of a Brazilian physics' teacher graduation during one of its disciplines, about topics related to mechanics. Our organizational structure was drawn from works done by James Wertsch (2008) on narratives, from which we adapted two structures that Wertsch proposed with respect to narratives for the study of scientific explanation: specific explanations and explanatory schematic templates. We associated specific explanations with explicative moments proposed by Ogborn, Kress, Martins e Mcgillicuddy (1996) and the schematic explanatory templates to explanation types proposed by explanation philosophers – especially the Causal Mechanical model, the Unification approach and the functional explanations. In our empirical analyze we seek to identify teaching goals that the different types of scientific explanations identified intended to meet and We noticed a (unexpected) low occurrence of scientific explanation in the seminars we follow, beside a strong emphasis on education to provide training in mathematical problem solving abilities. We used those results to discuss issues related to training teachers to basic education in light of the way scientific explanations are used.

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-05-10T18:21:02Z No. of bitstreams: 1 2017 - Bianca Rangel Antunes da Silva.pdf: 2187606 bytes, checksum: 927fe528eb48db49953e8f982d4320d5 (MD5) / Made available in DSpace on 2018-05-10T18:21:02Z (GMT). No. of bitstreams: 1 2017 - Bianca Rangel Antunes da Silva.pdf: 2187606 bytes, checksum: 927fe528eb48db49953e8f982d4320d5 (MD5) Previous issue date: 2017-12-21 / During the drilling of oil wells, the pressure differential between the rock formation and the annular region can cause a filtration process and consequent invasion of drilling fluid into the rocks, causing irreversible damage to the well. Therefore, studies to control the properties of the well formed mudcake are fundamental. The mudcake formed should be thin and of low permeability, thus minimizing the filtration and the invasion of the fluid. The main purpose of this work was to study the characteristics of the filtration pie formed during the drilling process of oil wells, using non-Newtonian fluids that follow the Power law model, and applying the simplified theory of filtration adapted for non-Newtonian fluids to achieve the specific objective that was the lifting of the parameters of permeability, porosity, thickness and correction factor obtained from experimental data of filtered volume versus time, in Static conditions, at different pressures. Experimental results were obtained in different filtration conditions (pressure, viscosifier agent and weighting material) seeking to compare and know the mechanisms that control filtration in static conditions. Filtration tests were carried out at 300 psi, 500 psi and 700 psi, using a HTHP cell and prepared non-Newtonian drilling fluids containing xanthan gum (XG) and carboxymethylcellulose (CMC) as viscosifier agent, in addition to calcite and barite. Filtration parameters such as permeability, porosity, pie thickness, filtration time and filtered volume have been evaluated. The permeability of the pie was determined, with the aid of a software of estimation of parameters, using the simplified theory of filtration adapted for non Newtonian fluids proposed by Massarani and Coelho de Castro(1980). The results obtained were confronted with those obtained by other methodologies. The experimental tests also showed that the properties of the pie vary with the filtration pressure. / Durante o processo de perfura??o de po?os de petr?leo, o diferencial de press?o entre a forma??o rochosa e a regi?o anular pode ocasionar um processo de filtra??o e consequente invas?o de fluido de perfura??o nas rochas, causando opera??es irrevers?veis ao po?o. Por isso, s?o fundamentais estudos para controlar as propriedades da torta de filtra??o formada na parede do po?o. A torta formada deve ser fina e de baixa permeabilidade, minimizando assim a filtra??o e a invas?o do fluido. Este trabalho teve como objetivo principal estudar as caracter?sticas da torta de filtra??o formada durante o processo de perfura??o de po?os de petr?leo, utilizando fluidos n?o Newtonianos que seguem a lei da pot?ncia,e aplicando a teoria simplificada da filtra??o adaptada para fluidos n?o Newtonianos para atingir o objetivo espec?fico que foi o levantamento dos par?metros de permeabilidade, porosidade, espessura e fator de corre??o obtidos a partir de dados experimentais de volume de filtrado versus tempo, em condi??es est?ticas, em diferentes press?es.Foram obtidos resultados experimentais em diferentes condi??es de filtra??o (press?o, viscosificante e adensante) buscando comparar e conhecer os mecanismos que controlam a filtra??o em condi??es est?ticas. Foram realizados ensaios de filtra??o a 300 psi, 500 psi e 700 psi, utilizando uma c?lula HTHP e preparados fluidos de perfura??o n?o-Newtonianos contendo Goma Xantana (GX) e carboximetilcelulose (CMC) como viscosificantes, al?m de barita e calcita. Foram avaliados os par?metros da filtra??o como permeabilidade, porosidade, espessura da torta, tempo de filtra??o e volume de filtrado. A permeabilidadeda torta foideterminada, com o aux?lio de umsoftware de estima??o de par?metros, utilizando-sea teoria simplificada da filtra??o adaptada para fluidos n?o Newtonianos proposta por Massarani e Coelho de Castro (1980). Os resultados obtidos foram confrontados com os obtidos por outras metodologias. Os ensaios experimentais mostraram tamb?m que as propriedades da torta variam com a press?o de filtra??o.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2016-11-17T15:28:54Z No. of bitstreams: 1 Márcio Lembi Teles_.pdf: 1859021 bytes, checksum: 5dc2746be44c5f2b865c68ec0b4c0db0 (MD5) / Made available in DSpace on 2016-11-17T15:28:54Z (GMT). No. of bitstreams: 1 Márcio Lembi Teles_.pdf: 1859021 bytes, checksum: 5dc2746be44c5f2b865c68ec0b4c0db0 (MD5) Previous issue date: 2016-09-16 / Nenhuma / Este trabalho apresenta uma análise fatorial, através de fluidodinâmica computacional, do escoamento e transferência de calor para fluidos viscoplásticos a partir de um cilindro confinado entre paredes paralelas. Considera-se que as propriedades reológicas sensíveis à temperatura, o que acopla os problemas térmico e fluidodinâmico de forma bilateral. Foi desenvolvida uma formulação baseada no método estabilizado de elementos finitos Galerkin Mínimos Quadrados (GLS – Galerkin Leart-Squares) para a aproximação de escoamentos não newtonianos com transferência de calor e propriedades reológicas termodependentes. Esta formulação foi implementada em um código computacional próprio. Para a modelagem das tensões viscosa, foi utilizado um modelo de líquido newtoniano generalizado, com função viscosidade dada pelo modelo de Herschel-Bulkley regularizado conforme Papanastasiou e propriedades termodependentes – a tensão inicial de escoamento e o índice de consistência. Os resultados numéricos foram investigados utilizando os adimensionais: número de Reynolds (Re), número de Herschel-Bulkley (Hb), número de Prandtl (Pr), índice de potência (n) e coeficientes de dependência térmica (a* e b*). Foi realizado um planejamento experimental fatorial completo 2K, com objetivo de avaliar a influência destes parâmetros na taxa de transferência de calor, através do número de Nusselt (Nu), e na perda de carga localizada devido à obstrução do canal pelo cilindro. / This paper presents a factor analysis using computational fluid dynamics, flow and heat transfer for viscoplastic fluids from a cylinder confined between parallel walls. It is considered that the rheological properties sensitive to temperature, which couples the thermal and fluid dynamic problems bilaterally. It was developed a formulation based on stabilized finite element method Galerkin Least Squares (GLS - Galerkin Leart-Squares) for approaching non-Newtonian flow with heat transfer and rheological properties dependent terms. This formulation has been implemented in a proper computer code. For the modeling of viscous stresses, a generalized Newtonian fluid model was used, with viscosity function given by the Herschel-Bulkley regularized model as Papanastasiou and properties dependent terms – the initial yield stress and consistency index. The numerical results were investigated using the dimensionless: Reynolds number (Re), Herschel-Bulkley number (Hb), Prandtl number (Pr), potency index (n) and temperature dependence coefficients (a* and b*). It conducted a full factorial experimental design 2K, with objective to evaluate the influence of these parameters on the heat transfer rate, through the Nusselt number (Nu), and localized head loss due to the cylinder by duct obstruction.

The main objective of this research was to exploit the interrelations between the rheological behavior and nano-microstructure of complex fluids in solving two state-of-the-art problems, one in the field of biomedical engineering: controlling the amount and characteristics of bioaerosol droplets generated during coughing, and the other in the bitumen-heavy oil industry: characterizing the nano-microstructure of asphaltene particles in bitumen and heavy oil from their rheological behavior. For the first problem, effect of viscoelastic and surface properties of artificial mucus simulant gels on the size distribution and amount of airborne bioaerosol droplets generated during simulated coughing were investigated. The results revealed that suppressing the generation of bioaerosol droplets and/or reducing the number of emitted droplets to a minimum during coughing are practically achievable through modulation of mucus viscoelastic properties. While variation of surface tension did not show any change in the droplet size distribution, an increase in particle size was observed as the samples changed from elastic solid type to viscoelastic type to viscous fluid type samples. This knowledge will help in the development of a new class of drugs being developed at the University of Alberta, aimed at controlling the transmission of airborne epidemic diseases by modifying the viscoelastic properties of mucus. For the second problem, studies of viscoelastic behavior of Athabasca bitumen (Alberta) and Maya crude (Mexico) oil samples, along with their Nano-filtered and chemically separated-plus-reconstituted samples were performed. The results revealed that the rheological behaviors of the bitumen-heavy oil samples are governed by their multiphase nature. The rheological behavior of all feeds, permeates and retentate samples followed a single master curve over the entire temperature interval, consistent with that of a slurry comprising a Newtonian liquid plus a dispersed solid comprising non-interacting hard spheres. The behavior of asphaltenes in the reconstituted samples, however, was found to be significantly different from that in nanofiltered samples. The information about the characteristics and behaviors of asphaltenes obtained in this study will help better understand the asphaltene structures, and support the effort to determine solutions for numerous asphaltene-related industrial problems. In the long run, this knowledge will help to create more efficient extraction and upgrading processes for bitumen and heavy oils. / Thermo Fluids

The surface oscillations in a deformable wall are known to induce an instability in the adjacent flow even in the absence of inertia. This instability, if understood properly, can be exploited to generate a well-mixed flow pattern with improved transport coefficients in microfluidic systems, wherein the benefits of inertial instabilities can not be realised. In order to utilise the wall deformability in micro-devices as well as other biotechnological applications, the quantitative knowledge of the critical parameter for the on-set of instability and the nature of bifurcation in the region of transition point are essential. With this objective, a major portion of this thesis deals with the stability analysis of flow past a flexible surface. For Newtonian flow over a deformable solid medium, the analyses of hydrodynamic stability in two flow regimes are presented: the viscous mode instability in the limit of zero Reynolds number, and the wall mode instability in the limit of high Reynolds number. The flexible solid in both analyses is described as a neo-Hookean solid continuum of finite thickness. The previous work on viscous instability using the same solid model ignored the viscous dissipation in the solid. In the present study, a purely elastic neo-Hookean model is augmented to incorporate the viscous stresses accounting for the dissipative mechanism in an aqueous gel-like solid medium. The linear stability analysis for this neo-Hookean viscoelastic solid shows a dramatic influence of solid viscosity on the stability behaviour. The important parameter here is where ηr is the solid viscosity relative to the fluid viscosity and H is the solid-to-fluid thickness ratio. While the effect solid viscosity is stabilizing for a further increase in viscosity in the regime reduces the critical shear rate for transition, indicating a destabilizing influence of solid viscosity. The weakly nonlinear analysis indicates that the bifurcation is subcritical for most values of H when ηr =0. However, for non-zero solid viscosity, the analysis reveals a range of ηr for which the nature of bifurcation is supercritical. The results are in contrast to the behaviour for the Hookean (linear) elastic solid, for which the effect of solid viscosity is always stabilising and the bifurcation is subcritical for all values of H and ηr. For the wall mode instability, critical parameters for the linear and the neo-Hookean elastic solid are found to be very close. The weakly nonlinear analysis of the wall mode instability shows that the instability is driven to a supercritically stable branch, indicating the possibility of a stable complex flow pattern which is ) correction to the base flow. The amplitude of the supercritically bifurcated equilibrium state, A1e, is derived in the vicinity of the critical point, and its scaling with the flow Reynolds number is obtained. The nonlinear analysis is also carried out using the asymptotic analysis in small parameter Re−1/3. The asymptotic results are found to be in good agreement with the numerical solutions for For a polymeric flow over a deformable solid medium, the viscous instability is analysed by extending the viscous mode for the Newtonian fluid to the fluid with finite elasticity. The viscoelastic fluid is described by an Oldroyd-B model which introduces two additional parameters: the Weissenberg number, W , and β, the ratio of solvent-to-solution viscosity. The polymer viscosity parameter β is an indirect measure of polymer concentration with the extreme cases of β =1 representing the Newtonian fluid and β =0the upper convected Maxwell fluid. The analysis considers both the linearly elastic and the neo-Hookean models to describe the deformable solid. The analysis reveals the presence of two classes of modes: the finite wavelength modes and the shortwave modes. The behaviour of the finite wavelength modes is similar for both the models of solid medium. The effect of increasing fluid Weissenberg number and also increasing polymer concentration (achieved by reducing β below 1) on the finite wavelength instability is stabilising. The viscous instability ceases to exist for W larger than a certain maximum value Wmax. The behaviour of the shortwave mode is remarkably different for both the models of solid. Using the shortwave asymptotic, the differences are elucidated and it is shown that the shortwave instabilities in both the models are qualitatively different modes. For a linear elastic solid model, the shortwave mode is attributed to the normal-stresses in polymeric fluid with high Weissenberg number. This mode does not exist for the Newtonian flow and is a downstream travelling disturbance wave. On the other hand, the shortwave mode for the neo-Hookean model is attributed to the normal-stress difference in the elastic solid. Hence, this mode does exist for the Newtonian fluid and is an upstream travelling disturbance wave. The role of polymer concentration in the criticality of finite wavelength and shortwave modes is examined for a wide range of Weissenberg number. The results are condensed in a map showing the stability boundaries in parametric space covering β, W and H. The weakly nonlinear analysis reveals that the bifurcation of linear instability is subcritical when there is no dissipation in the solid. The nature of bifurcation, however, changes to supercritical when the viscous effects in the solid are taken into account. The final problem of this thesis deals with the flow past a rigid surface. Here, the stability of base profile in a plane Couette flow of dilute polymeric fluid is studied at moderate Reynolds number. Three variants of Oldroyd-B model have been analysed, viz. the classical Oldroyd-B model, the diffusive Oldroyd-B model, and the non-homogeneous Oldroyd-B model. The Newtonian wall modes are modified marginally for the polymeric fluid described by the classical Oldroyd-B model. The Oldroyd-B model with artificial diffusivity introduces the additional ‘diffusive modes’ which scale with P´eclet number. The diffusive modes become the slowest decaying modes, in comparison to the wall modes, for large wavenumber disturbances. For these two models, the polymeric flow is linearly stable. Using the equilibrium flow method, wherein the nonlinear flow is assumed to be at the transition point, the finite amplitude disturbances are analysed, and the threshold energy necessary for subcritical transition is estimated. The third variant of Oldroyd-B model accounts for non-homogeneous polymer concentration coupled with the stress field. This model exhibits an instability in the linear analysis. The ‘concentration mode’ becomes unstable when the fluid Weissenberg number exceeds a certain transition value. This instability is driven by the stress-induced fluctuations in polymer number density.

Chemical modification is an important way to improve the properties of existing polymers, and one of the important examples is the hydrogenation of nitrile butadiene rubber (NBR) in organic solvent by homogeneous catalysis in order to extend its application. This process has been industrialized for many years to provide high performance elastomers (HNBR) for the automotive industry, especially those used to produce components in engine compartments. In the current commercial process, a batch reactor is employed for the hydrogenation step, which is labor intensive and not suitable for large volume of production. Thus, novel hydrogenation devices such as a continuous process are being developed in our research group to overcome these drawbacks. In order to make the process more practical for industrial application, high concentration polymer solutions should be targeted for the continuous hydrogenation. However, many problems are encountered due to the viscosity of the high concentration polymer solution, which increases tremendously as the reaction goes on, resulting in severe mass transfer and heat transfer problems. So, hydrogenation kinetics in high concentration NBR solution, as well as the rheological properties of this viscous solution are very essential and fundamental for the design of novel hydrogenation processes and reactor scale up. In the present work, hydrogenation of NBR in high concentration solution was carried out in a batch reactor. A commercial rhodium catalyst, Wilkinson’s catalyst, was used with triphenylphosphine as the co-catalyst and chlorobenzene as the solvent. The reactor was modified and a PID controller was tuned to fit this strong exothermic reaction. It was observed that when NBR solution is in a high concentration the kinetic behavior was greatly affected by mass transfer processes, especially the gas-liquid mass transfer. Reactor internals were designed and various agitators were investigated to improve the mechanical mixing. Experimental results show that the turbine-anchor combined agitator could provide superior mixing for this viscous reaction system. The kinetic behavior of NBR hydrogenation under low catalyst concentration was also studied. It was observed that the hydrogenation degree of the polymer could not reach 95% if less than 0.1%wt catalyst (based on polymer mass) was used, deviating from the behavior under a normal catalyst concentration. The viscosity of the NBR-MCB solutions was measured in a rotational rheometer that has a cylinder sensor under both room conditions and reaction conditions. Parameters that might affect the viscosity of the solutions were studied, especially the hydrogenation degree of polymer. Rheological properties of NBR-MEK solutions, as well as NBR melts were also studied for relevant information. It is concluded that the hydrogenation kinetics deviates from that reported by Parent et al. [6] when polymer is in high concentration and/or catalyst is in low concentration; and that the reaction solution (HNBR/NBR-MCB solution) deviates from Newtonian behavior when polymer concentration and hydrogenation degree are high.

Single ventricle congenital heart defects afflict 2 per every 1000 births. They are characterized by cyanotic mixing between the de-oxygenated blood coming back from the systemic circulation and the oxygenated blood from the pulmonary circulation. Prior to introduction of the Fontan procedure in 1971, surgical options for single ventricle patients were limited. The Fontan operation involves a series of three palliative procedures aimed at the separation of systemic and pulmonary circulations and reducing the long term effects of chronic hypoxia and ventricular volume overload. The total cavopulmonary connection (TCPC) is completed in the final stage of the surgery with the anastomosis of the inferior vena cava (IVC) and superior vena cava to the pulmonary arteries. Improved quantification and visualization of flow structures within the TCPC has the potential to aid in the planning and design of the Fontan operation. Despite significant development of phase contrast magnetic resonance imaging (PC MRI) for in vivo flow measurements, it is not routinely applied in children with single ventricle congenital heart disease. Limited technologies available for post-processing of PC MRI data has prevented clinicians and scientists from conducting the detailed hemodynamic analyses necessary to better understand the physiology of the single ventricle circulation. This thesis attempts to bridge the gap between PC MRI and fluid dynamics, by developing the necessary post-processing technologies for PC MRI, and then applying these techniques for characterizing single ventricle hemodynamics.