[pt] Ao longo deste trabalho, diversas características importantes para a dinâmica do escoamento intermitente foram analisadas experimentalmente. Todos os testes foram realizados numa tubulação com 0,0508 m de diâmetro interno, em configuração horizontal, utilizando água e ar e abrangendo uma região onde o escoamento passa por uma complexa transição do regime de bolha alongada, caracterizado por longas bolhas de gás localizadas próximo ao topo da tubulação, para o regime golfada, caracterizado por uma intensa quantidade de bolhas dispersas de gás e bolhas alongadas com formatos distorcidos e frentes mais distantes do topo da tubulação. Nesta região verifica-se uma notável carência de técnicas experimentais capazes de extrair informações quantitativas dos fenômenos característicos desses regimes. Através de um sistema de interruptores de feixe de infravermelho, o comportamento estatístico dos comprimentos dos pistões de líquido, das frequências de passagem dos pistões e do comprimento da bolha alongada puderam ser investigados. Uma extensa comparação dos dados com trabalhos disponíveis na literatura foi realizada, validando os resultados experimentais obtidos. Em conjunto, foi utilizada a técnica óptica, não intrusiva, conhecida como técnica de sombra (shadow technique), combinada com uma câmera digital de alta taxa de aquisição de imagens. Um procedimento inovador de processamento das imagens foi desenvolvido, permitindo a extração de informações quantitativas de regimes complexos com intensa quantidade de bolhas dispersas. Resultados importantes como o abaixamento do nariz da bolha como uma função da competição entre as forças de gravidade e de inércia puderam ser verificados e confirmados quantitativamente pela primeira vez. / [en] The present work experimentally studied several relevant dynamic characteristics of gas-liquid intermittent flow through a horizontal pipe. All tests were performed in a test section formed by 50.8 mm internal diameter pipe using air and water as working fluids. The tests covered a region where the flow undergoes a complex transition from elongated bubble flow regime, characterized by long gas bubbles located near the top of the pipe, to the slug flow regime, characterized by a large amount of dispersed gas bubbles in the liquid slug and elongated bubbles with distorted shapes and fronts displaced from the top of the pipe. In this region there is a notable lack of experimental techniques capable of extracting quantitative information of the characteristic dynamic phenomena involved. A set of infrared optical switches was employed to obtain statistical information on liquid piston lengths and frequency, as well as the elongated bubble lengths. An extensive comparison of the data obtained with works available in the literature was performed, validating the experimental results and the technique employed. Also, a high frame rate camera with back illumination was employed to capture images of the nose and tail of gas bubbles. An innovative procedure for image processing was developed, allowing for the extraction of original quantitative information on the complex shapes of the bubble and its relationship with flow variables. Relevant information such as the lowering of the bubble nose as a result of competing gravitational and inertial forces could be verified and confirmed quantitatively seemingly for the first time.

Espumas gás-líquido são sistemas coloidais constituídos de bolhas de ar separadas por filmes finos de líquido, sendo estabilizadas cineticamente pela presença de tensoativos. O uso de substâncias antiespumantes, torna-se necessário para que não haja perdas de matéria prima ou perda da eficiência de determinados processos. As misturas espumantes utilizadas neste trabalho foram soluções aquosas de dodecil sulfato de sódio (SDS) e dioctilsulfosuccinato de sódio (AOT), além de uma mistura de fermento biológico e melaço de cana em condições que simulam o processo de fermentação. Os antiespumantes comerciais são compostos principalmente por siliconas e poliéteres, que não são derivados de fontes renováveis. Esta dissertação apresenta resultados do estudo da ação antiespumante de ésteres etílicos com diferentes graus de saturação (derivados de sebo animal e de óleos de soja e babaçu), na presença ou não de partículas coloidais de sílica com superfície hidrofóbica. Dois métodos de geração de espuma foram utilizados, o de Barstch e o de Bikerman, e os parâmetros utilizados para avaliação da ação antiespumante foram: o volume de espuma formado, a velocidade de quebra da espuma e a velocidade de drenagem do líquido da espuma. De uma maneira geral, os resultados mostram que não é possível uma racionalização quanto ao efeito antiespumante e o grau de saturação dos ésteres utilizados, porém os mesmos apresentam boa atividade antiespumante e apresentam efeito sinérgico na presença de partículas hidrofóbicas apresentando, portanto, potenciais aplicações industriais, uma vez que sua ação é comparável ou, em alguns casos, melhor do que aquela observada para formulações comerciais. No caso particular das espumas estabilizadas com mosto a ação dos ésteres sobre a drenagem das espumas segue a ordem: soja <babaçu < sebo, sendo, portanto, o mais saturado aquele a apresentar o maior efeito. / Gas-liquid foams are colloidal systems formed by air bubbles separated by a liquid thin film stabilized by surfactants, which are often found in many industrial processes. It becomes often necessary the use of antifoams to avoid loses of material or loses in the processs efficiency caused by a large foam production. The foaming mixtures utilized in this work were aqueous solutions of sodium dodecyl sulfate, SDS, and sodium dioctylsulfosuccinate, AOT, besides a mixture of sugar syrup and yeast in conditions compared to that used in fermentation process. The commercial antifoams usually comprise silicones and polyethers petrol derivatives, so the use of natural derivative oils can be very interesting since they are biodegradable and are obtained of natural sources. This dissertation presents results of the antifoam effect of ethylic esters with different saturation degree (animal fatty, soy oil, and coconut oil derivatives) in the presence and the absence of hydrophobic silica. Two methods are employed for foam characterization: the Barstch and Bikerman tests. The parameters utilized to evaluate the antifoam efficiency are the foam volume, foam stability and drainage rate of the liquid. In a general way, the results show that there is not a rationalization about the different saturation degree and the antifoam efficiency, but they all present a good effect in the foam prevention, exhibiting a synergistic effect in the presence of hydrophobic silica indicating that upon an additional study they can become a market alternative for antifoams, since their effect are comparable or in some cases better than those measured for commercial formulations. In the particular case of the sugar syrup the effect of the esthers upon foam drainage follows the trend: soya<babassu<animal fat, being the most active the most saturated one.

The first part of this thesis investigates the mixing of ambient fluid into axisymmetric high Reynolds number gravity currents. A series of laboratory experiments were conducted in which small scale gravity currents travelled along a wedge shaped channel with an increasing width in the downstream direction. The channel was filled with fresh water and the current was generated using saline solution introduced either by a rapid release of a known finite volume from behind a lock gate or by pumping at a constant rate into the apex of the channel. The distribution and evolution of the density of the flow with distance downstream was measured using a light attenuation technique. Additional experiments were performed by injecting parcels of dye in different regions of the flow in order to visualise the motion of fluid in and surrounding the gravity current. Unlike currents introduced by the release of a finite volume of fluid, where most mixing occurs in the head of the flow, currents produced from a steady source develop a steady tail region behind the front which is also found to entrain a significant amount of ambient fluid. In both types of current, we estimate the fraction of displaced ambient fluid that is entrained into the flow. We then derive a new class of self-similar solutions for gravity currents produced from a finite volume release of fluid. The second part of this thesis develops the experimental method of measuring mixing using light attenuation to investigate the mixing of liquid in a vertical conduit which results from a continuous stream of high Reynolds number gas bubbles. The experiments identify that the mixing in the wake of the bubbles leads to a net dispersive transport along the conduit. The process provides an explanation for the heat transfer within a volcanic conduit in the case of a gas-slug flow regime as occurs in the near surface region of volcanic conduits connected to surface lava lakes. We derive a theoretical model to estimate the heat flux associated with such a system using the empirical law for the dispersive mixing. The predicted heat flux associated with the bubbles is found to be comparable to the heat loss at the surface of lava lakes associated with radiative and convective heat loss. Given values for the gas flux, the lake area and the temperature at the surface of the lake, the model enables new predictions for the size of the volcanic conduit.

This dissertation considers the genesis and dynamics of interfacial instability in vertical laminar gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory by means of Orr-Sommerfeld analysis together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. The influence of two main flow parameters on the interfacial dynamics, namely the film thickness and pressure drop applied to drive the gas stream, is investigated. To make contact with existing studies in the literature, the effect of various density and viscosity contrasts as well as surface tension is also examined. Energy budget analyses based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low and intermediate density contrast. Furthermore, high viscosity contrast and increases in surface tension lead to some amount of mode competition for thin film. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. These regions are extended at intermediate density contrast and exhibit only small changes with increased viscosity contrast or surface tension. Direct numerical simulations of the system with low density contrast show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. For high density contrasts corresponding more closely to an air-water-type system, linear stability theory is also successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times. Nevertheless, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic motion. Furthermore, linear stability theory also predicts when the direction of travel of the waves changes - from downwards to upwards. The practical implications of this change in terms of loading and flooding is discussed. The change in direction of the wave propagation is represented graphically for each investigated system in terms of a flow map based on the liquid and gas flow rates and the prediction carries over to the nonlinear regime with only a small deviation. Besides the semi-analytical and numerical analyses, experiments with an practically relevant setup and flow system have been carried out to benchmark and validate the models developed in this work.

Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 146-156). Also available for download via the World Wide Web; free to University of Oregon users.

Hydrogenation of nitrile butadiene rubber (NBR) has been carried out industrially for a number of years, producing a material with exceptional resilience to high temperatures and oxidative conditions. Current processes involve a batch reactor which is difficult to optimize further for larger scale production. A continuous process for this particular process is required in order to provide a large volume of production with consistent qualities. The integration of heat balance could be realized in a continuous process. A novel continuous process for hydrogenation of NBR has been developed in the present work. A multistage agitated contactor (MAC) was proposed as a gas liquid reactor for this process. Comprehensive hydrodynamic data have been acquired under various process conditions. The hydrodynamic behaviour under different operating variables such as stirring speed, liquid flow rate and gas flow rate has been understood through experimental study. It is found that an increase in stirring speed intensifies liquid backmixing while an increase liquid flow rate decreases liquid backmixing. The presence of gas flow helps in reducing liquid back mixing by two coupled effects: liquid entrainment effect due to a cocurrent operation manner and a strengthening effect of liquid flow rate due to its reduction of liquid hold-up. Contradictory conclusions regarding the effect of liquid viscosity on liquid backmixing in a MAC have been resolved through experimental investigation and computational fluid dynamics (CFD) simulations. It is shown that an increase in liquid velocity dampens turbulence which contributes to liquid phase backmixing within the reactor. The established hydrodynamic understanding of MACs in the present work widens its potential application for gas liquid process. Based on comprehensive understanding of the proposed reactor, a bench-scale prototype was designed and constructed in order to demonstrate hydrogenation performance. One more efficient catalyst for NBR hydrogenation, an osmium-based catalyst, was used in the present work. Hydrogenation degree of NBR in the continuous unit was investigated at operating conditions relevant to industrial applications. It is indicated from the experimental results that a desired hydrogenation degree of over 95% in 2.5% and 5% NBR solutions can be achieved at the conditions investigated. It is also shown that both system pressure and catalyst loading increase hydrogenation conversion. Mathematical modeling of the designed process was established by coupling the intrinsic catalytic hydrogenation from batch studies and flow behavior of the reactor. A cascade of stirred tanks with back flow (CTB) model was used to characterize the dynamic hydrogenation performance in a MAC. The comparison of experimental results and numerical prediction indicates that the established model could satisfactorily predict the hydrogenation in the designed process with consideration of approximately 30%-50% catalyst deactivated due to impurities and oxygen contamination in the polymer solution. A revised n CSTRs-in-series model was proposed to predict the hydrogenation degree at steady state and a good agreement was found when comparing the predicted results with the experimental data. A continuous process for hydrogenation at a pilot scale was designed based on the primary results from the bench scale process. A process with a capacity of 50 tons/year was targeted and the hydrogenation efficiency provided by the pilot scale unit has been estimated through the established reactor model.

The protic acid-catalyzed polymerization of 1,6-anhydro-6-D-glucopyranose (I) was first reported one-half century ago; however, the mechanism of this reaction has not been resolved and is the topic under investigation in this thesis. In an attempt to resolve this mechanism, a number of 1,6-anhydrides structurally related to 1,6-anhydro-B-D-glucopyranose (I) were prepared and polymerized. The C-2, C-3, or C-4 hydroxyl group was either specifically blocked, replaced by a hydrogen atom or positioned different sterically. The relative rates of disappearance of monomer in the polymerization reaction were measured and this information used to propose a reaction mechanism.

A generalized ejector model was successfully developed for gas ejector design and performance analysis. Previous 1-D analytical models can be derived from this new comprehensive model as particular cases. For the first time, this model shows the relationship between the cosntant-pressure and constant-area 1-D ejector models. The new model extends existing models and provides a high level of confidence in the understanding of ejector mechanics. “Off-design” operating conditions, such as the shock occurring in the primary stream, are included in the generalized ejector model. Additionally, this model has been applied to two-phase systems including the gas-liquid ejector designed for a Proton Exchange Membrane (PEM) fuel cell system. The equations of the constant-pressure and constant-area models were verified. A parametric study was performed on these widely adopted 1-D analytical ejector models. FLUENT, commercially available Computational Fluid Dynamics (CFD) software, was used to model gas ejectors. To validate the CFD simulation, the numerical predictions were compared to test data and good agreement was found between them. Based on this benchmark, FLUENT was applied to design ejectors with optimal geometry configurations.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on February 29, 2008) Vita. Includes bibliographical references.