No description available.

No description available.

This thesis deals with the mechanisms of microstructure development in polymer blends. Much work has been performed on the breakup process of immiscible systems where the dispersed phase is suspended inside another matrix. The fluids used were polymer melts or model viscoelastic fluids, and the processing flows were model shear flow or processing flows seen in industry. It is found that in industrial extruders or batch mixers, the morphology of the dispersed polymer evolves from pellets to films, and subsequently to fibers and particles. In this thesis, it is demonstrated based on force analysis that the in-situ graft reactive compatibilization facilitates breakup of the dispersed phase by suppressing slip at the interface of the dispersed phase and matrix phase. The morphology development of polymer blends in industrial mixers was simulated by performing experiments of model viscoelastic drop deformation and breakup under shear flow. Two distinct modes of drop deformation and breakup were observed. Namely, viscoelastic drops can elongate and breakup either in (1) the flow direction or (2) the vorticity direction. The first normal stress difference N1 plays a decisive role in the conditions and modes of drop breakup. Drop size is an important factor which determines to a great extent the mode of drop breakup and the critical point when the drop breakup mechanism changes. Small drops break along the vorticity direction, whereas large drops break in the flow direction. A dramatic change in the critical shear rate was found when going from one breakup mode to another. Polymer melts processed under shear flow present different morphology development mechanisms: films, fibers, vorticity elongation and surface instability. The mechanisms depend greatly on the rheological properties of both the dispersed and matrix phases, namely the viscosity ratio and elasticity ratio. High viscosity ratio and high elasticity ratio result elongation of the dispersed phase in the vorticity direction. Medium viscosity ratio and low elasticity ratio result in fiber morphology. Low viscosity ratio and high elasticity ratio result in film morphology. The surface instability is caused by the shear-thinning effect of the dispersed polymer. / Chemical Engineering

Thermoacoustic instability is of fundamental and applied interest in both scientific research and practical applications. This study aims to explore several very important sub-aspects in this field and contribute to a better understanding of thermoacoustic instability as encountered in typical gas turbines and rocket engines. Atomization has been recognized as a key mechanism in driving applied thermoacoustic instability. In this regard, this study mainly focuses on the atomization process relevant for delineation of thermoacoustic instability, contributing to a comprehensive understanding of the effect of acoustics on primary and secondary atomization. Firstly, a tree-based adaptive solver and VOF method are employed to simulate the jet primary atomization. The code is validated by theoretical, numerical and experimental results to demonstrate its capability and accuracy in terms of atomization in both low-speed and high-speed regime. Perturbation frequency and amplitude have shown to affect the atomization significantly. Besides, the effect of acoustic forcing on liquid ligament has also been numerically investigated. A volume source term is introduced to extend the solver to model the compressible effects in the presence of acoustic forcing. The influence of acoustic wave number, amplitude and frequency has been examined in detail. In terms of modelling the thermoacoustic instability, bifurcation analysis is carried out for a time-delayed thermoacoustic system using the Method of Line approach. Good predictions have been obtained to capture the nonlinear behaviors inherent in the system. Moreover, model-based simulation and control of thermoacoustic instability have been conducted. A low-order wave-based network model for acoustics is coupled with nonlinear flame describing function to predict the nonlinear instability characteristics in both frequency and time domain. Furthermore, active feedback control is implemented. Two different controllers have been designed to eliminate the thermoacoustic instability to an acceptably low level and may be employed in a practical manner.

abstract: Next generation gas turbines will be required to produce low concentrations of pollutants such as oxides of nitrogen (NOx), carbon monoxide (CO), and soot. In order to design gas turbines which produce lower emissions it is essential to have computational tools to help designers. Over the past few decades, computational fluid dynamics (CFD) has played a key role in the design of turbomachinary and will be heavily relied upon for the design of future components. In order to design components with the least amount of experimental rig testing, the ensemble of submodels used in simulations must be known to accurately predict the component's performance. The present work aims to validate a CFD model used for a reverse flow, rich-burn, quick quench, lean-burn combustor being developed at Honeywell. Initially, simulations are performed to establish a baseline which will help to assess impact to combustor performance made by changing CFD models. Rig test data from Honeywell is compared to these baseline simulation results. Reynolds averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence models are both used with the presumption that the LES turbulence model will better predict combustor performance. One specific model, the fuel spray model, is evaluated next. Experimental data of the fuel spray in an isolated environment is used to evaluate models for the fuel spray and a new, simpler approach for inputting the spray boundary conditions (BC) in the combustor is developed. The combustor is simulated once more to evaluate changes from the new fuel spray boundary conditions. This CFD model is then used in a predictive simulation of eight other combustor configurations. All computer simulations in this work were preformed with the commercial CFD software ANSYS FLUENT. NOx pollutant emissions are predicted reasonably well across the range of configurations tested using the RANS turbulence model. However, in LES, significant under predictions are seen. Causes of the under prediction in NOx concentrations are investigated. Temperature metrics at the exit of the combustor, however, are seen to be better predicted with LES. / Dissertation/Thesis / M.S. Mechanical Engineering 2012

L'instabilité de Rayleigh-Plateau est utilisée dans les dispositifs d'impression à jet continu (CIJ) afin de piloter la dynamique de brisure des jets d'encre. Son étude dans ce cas de figure s'inscrit dans un cadre pluridisciplinaire relevant de la mécanique des fluides, de la rhéologie, ou encore de la physique des polymères. Le travail effectué se focalise sur l'influence des propriétés du fluide ainsi que de la géométrie de la buse d'impression sur cette dynamique. Ainsi, la caractérisation expérimentale des propriétés physicochimiques et rhéométriques des encres fait l'objet d'une attention particulière. La dynamique de brisure est ensuite modélisée à l'aide de différents logiciels de simulation numérique puis comparée aux expériences effectuées par ailleurs. Ces simulations prennent en compte lorsque c'est le cas les comportements non newtoniens des encres étudiées telles que leur propriétés rhéofluidifiantes ou viscoélastiques. Un lien étroit entre la dynamique de brisure et la forme du profil de vitesse en sortie de la buse est mis en évidence. Ce lien semble constituer une piste d'investigation particulièrement intéressante dans le cadre de la prédiction des dynamiques de jets obtenues par les dispositifs d'impression industriels. / Rayleigh-Plateau instability is used in continuous ink jet (CIJ) printers in order to drive ink jets breakup. Studies of such mechanisms are based on pluri-disciplinary concepts dealing with fluid mechanics, rheology and polymer sciences. The present work focuses on fluid properties and nozzles designs influences onto breakup dynamics. In this context, the experimental characterization of ink physical and rheological properties are of particular interest. Thereafter, jet dynamics computations are performed using several software and compared with experiences. Potential non Newtonian behaviours such as shear-thinning or viscoelasticity are modelled by computations. A close link between breakup dynamics and velocity profile at the nozzle exit is highlighted. This link is believed to bring crucial information for the prediction of jet dynamics observed in industrial printers.

[pt] Na produção de petróleo, durante a recuperação secundária, a injeção de água no reservatório de petróleo com o objetivo de deslocar o óleo até o poço produtor pode levar a um regime de escoamento bifásico onde ocorre a formação de emulsões. As emulsões são um problema para a indústria do petróleo porque produzem perda de carga nas linhas de produção e tornam difíceis os processos de separação óleo-água, gerando altos custos. Este fenômeno ainda não é bem entendido e não é exclusivo do que ocorre no meio poroso porque também está presente nas diferentes etapas da produção de petróleo. Este trabalho foi focado na formação de emulsões no meio poroso de um reservatório, considerando especialmente o escoamento bifásico na escala de poros. Assim foi utilizada uma junção de micro canais em T para descrever o que poderia acontecer na união de duas gargantas de poros em um reservatório de petróleo. Neste caso utilizamos a técnica de formação de gotas por fluxo cruzado estudada e desenvolvida, nas últimas décadas, na área de micro-fluídica. Através da injeção de dois líquidos imiscíveis nos canais que formam a junção, foi estabelecido um regime estável de formação de gotas. Para estudar a influência das diferentes variáveis do processo na formação de gotas, foram variadas as vazões dos líquidos injetados e suas propriedades, como viscosidades e tensão interfacial. Os resultados mostram que os diferentes regimes de escoamento e formação de gotas observados não são só uma função do número de capilaridade da fase contínua, como sugere a literatura para junções micro-fluídicas T de seção retangular. Nos experimentos desenvolvidos neste trabalho, nos quais a seção reta dos canais é oval e a fase contínua é a fase aquosa, as características da fase dispersa, como vazão e viscosidade, tiveram uma grande influência no processo de formação de gotas. / [en] In oil production, during secondary recovery, water injection into the reservoir to displace oil towards the production well generates different phenomena, among which is emulsion formation. Emulsions are a problem for the oil industry, because they change the pressure drop in production lines and hardens the process of separating oil-water, generating high operating costs. Emulsion formation in oil production is not yet well understood and it does not only occur in porous media, emulsion formation also occurs during different stages of oil production. This work was focused on the emulsion formation in porous media specifically considering the pore scale two phase flow. A T-junction microfluidic device was used as a model of the union of two pore throats in a porous media. We studied droplet formation in cross-flowing streams, a technique studied and developed in the past decade in the area of microfluidics technologies. Through the injection of two immiscible liquids in the channels of the device, we established a stable droplet formation regime. To study the influence of different variables that govern drop formation, we varied the flow rates of both immiscible phases and their properties, such as viscosity and interfacial tension. The results show that the different regimes observed are not only a function of capillary number, defined based on the continuous phase, as suggested in the literature for microfluidic T junctions with rectangular cross section. In our experiments the cross section of the channel had an elliptic shape and the continuous phase was aqueous, and the characteristics of the dispersed phase had a great influence in the process of drop formation.

[pt] Uma câmera de alta velocidade foi utilizada para visualizar o processo de quebra de gota em um misturador rotor - estator e através de um orifício em um duto em condições de escoamento turbulento. Dois casos especiais foram considerados: quebra de emulsões diluídas e quebra de gotículas de óleo individuais. Dois óleos minerais de viscosidade moderada foram dispersos em duas fases continuas diferentes, água da torneira e uma fase contínua formada por uma mistura de água do mar padrão e o surfactante aniônico STEOL CS-330 (Stepan Company). No caso de quebra no misturador rotor - estator, dois mecanismos foram identificados. Uma fragmentação inicial é causada pela combinação do vórtice (gerado pelo movimento circular do rotor) e a região de jato emergente dos furos do estator. O segundo mecanismo é uma quebra mecânica causada pelas altas taxas de cisalhamento que as gotas sofrem na abertura entre o rotor e o estator. No caso de quebra através do orifício, foi mostrado que a ruptura das gotículas ocorre somente a jusante da restrição, após percorrida certa distancia a partir da borda do orifício. Nesse comprimento de quebra, o gradiente radial de velocidade axial no escoamento é suficientemente grande para superar as tensões resistivas (exercidas pelas gotículas) e produzir a ruptura da gota. Esses resultados estão em concordância com as observações previas feitas por Galinat et al. (2005) para o caso de quebra de gota através de uma placa de orificio. No entanto, a partir das observações feitas neste trabalho, foi possível concluir que o comprimento do orifício não influencia os mecanismos de quebra. Também, a visualização permitiu analisar a influencia relativa da tensão interfacial e da viscosidade da fase dispersa para os dois casos considerados. Dados experimentais do tamanho de gota máximo estável foram obtidos para o caso de quebra de gota de emulsões de óleo em água diluídas nos dois casos estudados. A análise dos dados revelou que os tamanhos de gota máximos estáveis encontravam-se dentro da sub-faixa inercial, caracterizada exclusivamente pela taxa de dissipação de energia por unidade de massa, Épsilon. Um modelo mecanístico linear para a sub-faixa inercial, baseado na teoria de turbulência isotrópica de Kolmogorov, foi desenvolvido para ajudar na interpretação dos dados e suprir uma base para correlação. O modelo foi ajustado aos dados experimentais utilizando uma ferramenta de otimização não linear baseada no código GRG2 (Generalized Reduced Gradient), e sua precisão calculada a partir da raiz quadrada media das diferenças entre os dados experimentais e os previstos. Boas previsões foram obtidas para o rompimento no misturador, no entanto, este não foi o caso da quebra através do orifício. A baixa precisão relativa do modelo utilizado para correlacionar a quebra através do orifício reside na falta de consideração da escala de tempo requerida para a ruptura. Além disso, uma regressão linear baseada em um modelo Power Law mostrou que os efeitos interfaciais dominam o processo de quebra de gota na restrição. / [en] A high-speed camera has been used to visualize the drop breakup process at turbulent conditions in a rotor - stator mixer and through an orifice in a pipe. Two special cases were considered: the breakup of diluted emulsions and the breakup of single oil droplets. Two mineral oils of moderate viscosity were dispersed in two different continuous phases, tap water and a continuous phase formed by a mixture of substitute ocean water and the anionic surfactant STEOL CS-330 (Stepan Company). For the case of breakup in the rotor - stator mixer, two mechanisms were identified. An initial fragmentation is caused by the combination of the vortex (generated by the circular motion of the rotor) and the jet zone emerging from the stator holes. The second mechanism is a mechanical breakup caused by the high shear stresses that droplets suffer in the rotor - stator gap. In the case of breakup through an orifice in a pipe, it was shown that breakage only occurs downstream of the restriction and takes place at a certain distance from the edge of the orifice. At this breakup length, the radial velocity gradient in the flow is large enough to overcome the resistance stresses (exerted by the droplet) and produce the rupture of the droplet. These results were in agreement with previous observations made Galinat et al. (2005) for the case of drop breakup through an orifice plate. However, from the observations made in this work, it was possible to conclude that the orifice length does not influence the breakup mechanisms. In addition, visualization has allowed to analyze the relative influence of interfacial tension and dispersed phase viscosity for both cases. Experimental values for the maximum stable drop diameter were obtained for the breakup of diluted oil-in-water emulsions in both studied cases. Analysis of the data revealed that maximum stable drop sizes were in the inertial sub range, characterized exclusively by the energy dissipation rate per unit mass, Epsilon. A linear mechanistic model for the inertial sub-range, based in Kolmogorov s theory of isotropic turbulence, was developed to aid in data interpretation and to provide a basis for correlation. The model was adjusted to experimental data using a nonlinear optimization tool based in the generalized reduced gradient code (GRG2), and its precision was calculated from the root mean squared difference between experimental and predicted data. Good predictions were obtained for the breakup in the mixer; however, this was not the case for the breakup through the orifice. The relative low precision of the model used to correlate the breakup through the restriction lied in the lack of consideration of the time scale required for the breakup. In addition, a linear curve fitting based in a power law model, showed that interfacial effects drive the breakup process in the restriction.

The theoretical level of the divorce theme is based on specialized literature and other sources of information. In the theoretical part are defined the basic terms related to topics such as family, function of family, types of education, OSPOD activity, court activity, child's right of participation, etc. The data for the empirical part are obtained by semi-structured interview and processed qualitatively. The interviews were conducted with seven adolescents between the ages of 18 and 19 who have personal experience with the divorce/breakup of their parents. The aim of this thesis is to get an idea of how adolescents retrospectively perceive pass divorce/breakup of parents, with a time interval of 2-5 years. According to my finding, it has clearly emerged that family breakdown is a very demanding life situation for all involved, which brings about a lot of different changes. These changes are emerging in three basic categories that came from the data analysis (functional and dysfunctional family, divorce factors, fast loss of childhood and "adult" reconciliation).

Le but principal de ma thèse de doctorat est d’étudier la dissociation de noyaux exotiques. Ces noyaux sont peu liés et présentent une structure en halo dominante. Ceci conduit à des propriétés très particulières, telles que des rayons beaucoup plus grands que ceux des noyaux voisins. Les noyaux 6He et 11Li sont des exemples typiques, et sont décrits par des structures alpha+n+n et 9Li+n+n, respectivement. La principale technique expérimentale pour étudier ces noyaux consiste à développer des faisceaux d’ions radioactifs, et à mesurer la section efficace de dissociation sur des cibles lourdes. Les données expérimentales nécessitent donc le développement de modèles théoriques précis pour leur interprétation.<p><p>Mon travail a consisté en le développement de la méthode eikonale pour décrire les processus de diffusion élastique et de dissociation. Cette méthode nécessite les fonctions d’onde du projectile qui, dans le cas présent, est décrit par une structure à trois corps. Cette situation rend les calculs particulièrement difficiles, en particulier pour la réaction de dissociation où les fonctions d’onde du continu à trois corps sont nécessaires. Les fonctions d’onde à trois corps sont décrites dans le cadre des coordonnées hypersphériques, à la fois pour les états liés et pour les états de diffusion.<p><p>J'ai d'abord calculé les sections efficaces de dissociation de 6He en utilisant des fonctions d'onde & / Doctorat en Sciences / info:eu-repo/semantics/nonPublished