Miniemulsion technology is attracting increasing interest for the preparation of nano-size particles. However, the barrier to industrialising miniemulsion-based products is the lack of an energy efficient and scalable homogenisation device. Current laboratory techniques consist of batch units, however trends are leaning towards developing continuous processes. The objective of the work presented here is to investigate the use of the rotor-stator (RS) and static mixers (SM) as homogenisation devices and ultimately develop a continuous emulsification/polymerisation process for the preparation of miniemulsions. Initially we investigated the RS as a homogenisation device and found that we were able to generate droplets ranging from 300 nm to 2 μm, at industrially pertinent solids content. Subsequently, we investigated the use of SM and compared their performance in terms of mean droplet size evolutions with the rotor-stator. We were able to generate droplets < 200 nm in size and polymerise them in a stable fashion. All the available emulsification devices were then compared in terms of power/energy consumption, droplet size distributions and shear rates. It was observed that with energy costs being of similar orders of magnitude, SM imposed less shear, produced relatively narrow distributions and were better adapted to scale-up, making them the optimal choice for miniemulsification. Energy savings were increased by reducing coalescence during the emulsification step by using in situ generated surfactants, ultimately reducing emulsification time. Neutralising a water-soluble base with an oil-soluble acid almost instantaneously generates in situ surfactants at the oil-water interface. The reduction in emulsification time was partially attributed to the elimination of the relatively slow adsorption step typical of preformed surfactants. These results were used to show that emulsifying in situ formulations at moderate flow rates in line with SMX mixers can substantially reduce emulsification time from 30 minutes, with preformed surfactants, to ~30 seconds. With such a rapid emulsification step, it was possible to test the feasibility of the continuous emulsification process followed by polymerisation in a tubular reactor. Comparing this process with a batch operation, similar results for the ratio of NP/ND and conversion were obtained, but the continuous process was accomplished in a single step. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-04-19 03:32:08.766

Air velocity and fuel concentration data have been collected throughout the flow fields of two gas turbine mixers in an effort to better understand the mixing of fuel and air in gas turbine mixers. The two gas turbine mixers consisted of an annular flow profile and incorporated swirl vanes to produce a swirling flow to promote fuel/air mixing. The fuel was injected into the bulk flow from the pressure side of the swirl vanes. The first mixer had a swirl angle of 45°, while the second had a swirl angle of 55°. In order to examine the effect of the swirl angle on the mixing of fuel and air as the flow progressed through gas turbine mixers, axial and tangential air velocity data was taken using a laser Doppler velocimeter (LDV). Also, fuel concentration data was taken separately using a hydrocarbon concentration probe with methane diluted with air as the fuel. The data were taken at varying axial and varying angular locations in an effort to capture the spatial development of the fuel and velocity profiles. The spectra of the data were analyzed as well in an effort to understand the turbulence of the flow. It was found that the 55° swirler exhibited smaller variations in both velocity and fuel concentration values and that the fuel reached a uniform concentration at axial locations further upstream in the 55° degree mixer than in the 45° mixer. The RMS values of the velocity, which were influenced by the swirl vanes, were higher in the 55° mixer and likely contributed to the better mixing performance of the 55° mixer. The fuel concentration spectrum data showed that the spectra of the two mixers were similar, and that the fluctuations in fuel concentration due to flow emanating from the swirl vanes were seen throughout the length of the two mixers.

No description available.

Au cours de cette étude du procédé de granulation humide, nous avons mis l’accent sur l’intérêt que présente la distribution du liquide de mouillage dans la définition des propriétés finales de grains. Dans ce cadre, une méthode utilisant un traceur a été développée pour le suivi cinétique de la répartition du liquide de mouillage au cours de la granulation. Une formulation à base d’excipent pharmaceutique a été granulée dans un mélangeur-granulateur à haut cisaillement Mi-Pro. On a pu ainsi montrer que le début du procédé est caractérisé par l’hétérogénéité de la distribution du liquide de mouillage qui se redistribue ensuite selon une loi cinétique d’ordre un. Les propriétés des grains (taille, porosité et observation microscopique) ne deviennent uniformes qu’après une répartition homogène du liquide de mouillage entre les différentes classes de grains. L’étude de l’influence de certaines variables opératoires (vitesse d’agitation, débit et critère de mouillabilité) sur le phénomène de redistribution a été également menée. Par ailleurs, les bilans de population ont été utilisés comme outil de modélisation. Des écritures du noyau d’agglomération ont été proposées en se basant sur la taille des particules et leur teneur en liquide de mouillage. Bien que reproduisant les résultats expérimentaux, les bilans de population présentent certaines limites liées à la difficulté d’intégrer toutes les données de l’étude / In this study of wet granulation process, we are especially interested in binder liquid distribution as a mean to deduce final granule properties. Then, a tracer method is developed to study binder liquid distribution kinetics during granulation process. Granulation experiments are carried out in high shear mixer Mi-Pro using pharmaceutical excipients. The beginning of the process is characterized by heterogeneous binder liquid distribution. Then, liquid redistribution phenomenon is observed according to a first order model. Granule properties (size, porosity, microscopic observation) are found to be similar when binder liquid is homogeneously distributed among different granule classes. Finally operating conditions influence (speed rate, flow rate and wetting criterion) are discussed. In addition, population balances are used as a tool to model experimental results. Agglomeration kernels are presented depending on particle size and binder liquid ratio. Although experimental results could be satisfactorily modelled, population balances show some limitations related to the difficulty of integrating all the study data

MSc., Faculty of Science, University of the Witwatersrand, 2011 / A hierarchical non-linear model was developed for the time-dependent shrinkage behaviour of South African concretes, from historical laboratory data. The fit of fifteen growth curve models to the shrinkage-time profiles was evaluated and MCDA was used to identify the best model. The three parameters of the chosen growth curve model were modelled in terms of covariates (relating to concrete raw materials, concrete composition and shrinkage testing conditions) by multivariate multiple regression to produce the WITS model. The model largely conformed to existing knowledge about the factors affecting concrete shrinkage. Published models for concrete shrinkage were compared to the WITS model regarding their predictive ability with respect to the South African data set. The WITS model performed the best across a variety of graphical and numerical goodness-of-fit measures. The importance of the study is two-fold:  The concept of hierarchical non-linear modelling has been applied for the first time to the modelling of the time-dependent properties of concrete.  This is the first comprehensive model to bring together laboratory data on the shrinkage of concrete generated in South Africa over a span of thirty years.

Cette étude porte sur l'émulsification en continu du bitume à l'aide de mélangeurs statiques de type SMX, dans le domaine des émulsions concentrées, voire très concentrées. Ce travail suit une approche intégrant trois types de paramètres : procédé, formulation physico-chimique et composition, avec pour objectif ultime la maîtrise de la taille de gouttes. Il a été montré qu'une combinaison de fortes teneurs en bitume et de hautes températures d'émulsification favorisent l'obtention de très petites tailles de gouttes (diamètre médian inférieur ou égal à 1 µm). Cette observation contraste avec l'émulsification à forte teneur en phase dispersée en procédé discontinu. Ces résultats mettent en évidence une compétition entre les aspects énergétiques de l'émulsification et la formulation physico-chimique. Il a été mis en évidence, que lors de l'émulsification en continu à des fractions massiques en bitume supérieures à 90 %, la taille des gouttes n'est pas une fonction de l'énergie fournie mais que ce sont les paramètres de formulation qui contrôlent l'émulsification. Le suivi de la cinétique de l'émulsification et de la morphologie de l'émulsion au cours du processus d'émulsification a montré que le mécanisme d'émulsification à très fortes concentrations en bitume (90 % massique) passe par une étape d'inversion de phases catastrophique, suivie d'un affinage de l'émulsion dû aux effets de cisaillement et d'élongation lors de la phase finale de mélange. Une méthodologie basée sur une analogie de Poiseulle pour la mesure en ligne de la viscosité de procédé a été développée, permettant l'évaluation in-line du comportement rhéologique d'un fluide à travers des mesures de débit et de perte de charge / This work focuses on the continuous emulsification process (using SMX static mixers) of bitumen for concentrated and highly concentrated emulsions. This work uses an approach that integrates the process, the physic-chemical formulation and composition parameters, with the main objective of controlling the drop size of the emulsions. It was shown that the emulsification carried out at high bitumen concentrations and high temperatures favours the production of emulsions with very small droplets sizes (mean diameter ? 1 mm). This is in contrast with emulsification process in batch mode, in the same concentration and temperature conditions. These results demonstrate the competition between energy and physic-chemical formulation aspects. It was also revealed that when continuous emulsification is carried out at 90 % wt. of bitumen, droplet sizes are not a function of the energy provided and, hence, the emulsification process is controlled by the formulation parameters. Morphological analyzes, coupled with kinetics of emulsification obtained by in-situ monitoring of the viscosity, allowed the description of the mechanisms occurring during the emulsification at high internal phase ratio. It was possible to identify two principal steps in the mechanism: a catastrophic phase inversion followed by a droplet reduction by agitation, the largest size reduction being achieved thanks to the effects of shear and elongation in the static mixer. An inline process viscosity measurement methodology was developed. This methodology, based on a Poiseuille analogy, allows the evaluation of the rheological behavior of a fluid through flow rate and pressure drop measurements

This thesis explores the design and applications of subharmonic mixers in CMOS microwave integrated circuits. First, a 2x down-converting subharmonic mixer is demonstrated with a measured conversion gain of 8 dB using a 2.1 GHz RF signal. Extending the concept of the 2x subharmonic mixer, a 4x subharmonic mixer is proposed that operates in the 12 GHz Ku-band. This circuit is the first 4x subharmonic mixer in CMOS, and achieves a 6 dB conversion gain, which is the highest for any 4x subharmonic mixer regardless of circuit topology or fabrication technology. Furthermore, it achieves very high measured isolation between its ports (e.g. 4LO-RF: 59 dB). Since both the 2x and the 4x subharmonic mixers require a quadrature oscillator, a new oscillator circuit is presented that could be used with either of the aforementioned mixers. This quadrature oscillator uses active superharmonic coupling to establish the quadrature fundamental relationship. The oscillation frequency is 3.0 GHz and the measured output power is -6 dBm. A dual-band mixer/oscillator is also demonstrated that can operate as either a fundamental mixer or a subharmonic mixer depending on a control voltage. This circuit operates from 5.0 GHz to 6.0 GHz or from 9.8 GHz to 11.8 GHz by using either the fundamental output or the second harmonic output of the quadrature oscillator circuit described above and achieves conversion gain over both frequency bands. A novel frequency tripler circuit is presented based on a subharmonic mixer. This circuit uses the 2x subharmonic mixer discussed above, along with a feedforward fundamental cancellation circuit. The measured fundamental suppression is up to 30 dB and the conversion gain is up to 3 dB. Finally, a frequency divider circuit based on a subharmonic mixer is presented that divides the input signal frequency by a factor of three. This circuit uses a single-balanced version of the 2x subharmonic mixer described above in a regenerative divider topology. The measured input signal bandwidth is 300 MHz (5.2 GHz to 5.5 GHz) with an input power of -7 dBm and the maximum conversion gain is 0 dB. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2009-03-24 16:08:31.805

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Une installation de mélange rapide entièrement automatisée permet d'étudier l'influence des conditions de mélange sur la co-précipitation d'oxydes mixtes de cérium et de zirconium. L'intensité du mélange est contrôlée par le débit d'entrée des solutions réactives. Un modèle d'engouffrement à iso-volume a permis d'estimer le temps de mélange à partir de la mesure d'un indice de ségrégation par le système de Villermaux Dushman pour trois mélangeurs Hartridge Roughton de géométries différentes. Pour une même puissance spécifique dissipée, le mélange est plus intense lorsqu'un rétrécissement est présent. L'intensification du mélange diminue la température maximale de réductibilité et augmente les contraintes du réseau cristallin des oxydes mixtes synthétisés et calcinés à 1100 °C. Cela est interprété par une meilleure homogénéité des particules. L'étude des particules directement en sortie du mélangeur rapide montre que pour les débits étudiés le mélange parfait avant précipitation n'est pas atteint. Une partie des particules se forme en milieu acide, incorporant des nitrates dans leur structure. Une modélisation simple des phénomènes de mélange couplée à une prise en compte des équilibres chimiques confirme ce résultat expérimental. / An automated experimental set-up with rapid mixers is used to study the influence of mixing conditions on the co-precipitation of cerium-zirconium mixed oxides. The intensity of mixing is controlled by the inlet flowrates of the reacting solutions. An engulfment model is used to estimate a mixing time from the measurement of a segregation index by the Villermaux-Dushman reaction system. Three geometries of Hartridge Roughton mixers are compared. Mixing performance is better when a separate mixing chamber upstream of a narrower outlet pipe is present. A better mixing decreases the maximal reducibility temperature of the material and increases the crystal strains of the particles calcined at 1100 °C. This is probably due to a better homogenization of the particles content. The important incorporation of nitrates in the particle at the outlet of the mixers shows precipitation occurs while the mixing process is not finished. This experimental result was confirmed by numerical simulation and an estimation of sursaturations during the mixing process.