Une configuration en T-jonction a été étudiée pour sa simplicité en géométrie en comparant avec d’autres mélangeurs en industrie. Plus particulièrement, j’ai effectué des simulations numériques directes avec OpenFOAM des T-jonction convergent à section circulaire et rectangulaire. Les fluides Newtonien et non-Newtonien (modèle Bird-Carreau) ont été pris en compte. Dans un premier temps, j’ai comparé mes données avec le travail expérimental de Nguyen [1] sur le T-jonction circulaire en régime deflecting. J’arrive à valider la DNS avec les données expérimentales. L’organisation des structures cohérentes sont illustrées en régime laminaire et turbulent en Newtonien et en non-Newtonien. Dans un deuxième temps, j’ai simulé deux régimes (deflecting et impinging) dans un T-jonction rectangulaire en Newtonien et en non-Newtonien. J’ai montré l’existence de structures cohérentes (par example kidney vortex) qui servent de moteur au mélange du scalaire passif propre au non-Newtonien. L’efficacité de mélange est augmentée en régime impinging par rapport au régime deflecting. Le shifting du pic de turbulence est observé uniquement en régime impinging. / For the simplicity in geometry by comparing it with other mixers in the industry, flows in T-junction configuration have been studied. More specifically, Direct Numerical Simulations is carried out using OpenFOAM on a convergent T-junction configuration with circular and rectangular cross-section. Both Newtonian and non-Newtonian fluids (Bird-Carreau model) are taken into account. Firstly, DNS data is compared to Nguyen’s experimental work on the circular T-junction at regime deflecting [1]. Good agreement between simlation and experiment is achieved. The organization of coherent structures is illustrated in laminar and turbulent for both Newtonian and non-Newtonian cases. Secondly, two flow regimes (deflecting and impinging) are simulated in a rectangular T-junction for the same Newtonian and non-Newtonian fluids. The existence of non-Newtonian coherent structures (e.g. kidney vortex ) is shown. These structures are regarded as essential mixing mechanism of passive scalar mixing. The mixing efficiency is increased in regime impinging compared to regime deflecting. The shifting of the turbulence peak is only observed in regime impinging.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19234号 / 工博第4069号 / 新制||工||1628(附属図書館) / 32233 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 渡辺 宏, 教授 古賀 毅, 教授 金谷 利治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

To confirm computer simulations and Computational Fluid Dynamics (CFD) analysis, benchtop experiments are needed with a fluid that mimics blood and its viscoelastic properties. Blood is challenging to use as a working fluid in a laboratory setting because of health and safety concerns. Therefore, a blood analogue is necessary to perform benchtop experiments. Viscosity is an important property of fluids for modeling and experiments. Blood is a shear thinning fluid, so it has a decreasing viscosity with higher shear rates. This project seeks to create a blood mimicking fluid for benchtop laboratory use. Numerous fluids with different combinations of water, glycerin, and xanthan gum were created to mimic the shear thinning property of blood at different hematocrit levels. Since the amount of xanthan gum is very small, an analytical balance was used. To mix the solution, an immersion blender and a heat circulator were used. The data were obtained from 10-90 torque percent, which is the range over which the rheometer is accurate, so the exact ranges of shear rate tested depended on the test fluid. The created solutions were compared to blood at the equivalent hematocrit and previously performed tests.The three different equivalent hematocrits all produced results similar to viscosities of blood. The results were similarly representative of blood at different equivalent viscosities for the 0.0075% xanthan gum and the 0.075% xanthan gum by weight. The solutions were able to mimic the shear thinning behavior of blood at different equivalent hematocrits. The fluids with 0.075% xanthan gum and 50% water and 50% glycerin is a better representative than the fluids with 0.075% xanthan gum and 60% water and 40% glycerin.

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<p>Highly shear-thinning polymers that can easily flow upon the application of shear but form gels at rest have multiple potential applications in the eye. In the front of the eye, a formulation that can easily be administered via a conventional eye dropper but form a gel within the tear film once applied would be beneficial for prolonging drug release at the front of the eye, either alone or as a medium for entrapping nanoparticles or nano-objects loaded with drugs. In the back of the eye, vitreous substitutes that can be administered through a narrow gauge needle (and, ideally, removed via the same) may be beneficial for retinal surgeries.</p> <p>The overall objective of the proposed research is to chemically modify PVP through grafting strategies to improve its viscometric and mucoadhesive properties while maintaining the beneficial properties, which make it useful in ophthalmic applications.</p> <p>N-vinylpyrrolidone is copolymerized with N-vinylformamide to produce a functionalized grafting platform P(VP-co-VF), which is then grafted with low concentrations of short hydrophobic grafts to introduce non-Newtonian flow profile to the precursor.</p> <p>For applications at the back of the eye, the hydrophobic grafted PVP can be injected into the vitreous cavity of the eye in a liquid form to form subsequently a gel-like substance and function as a substitute for the vitreous humour. For application at the front of the eye, the shear thinning properties of hydrophobic-grafted PVP is combined with the mucoadhesive properties of phenylboronic acids (PBA) to improve the bioavailability of the drugs delivered to the front of the eye with eye drops.</p> <p>Rheological characterization of the solutions has shown the potential to form gel-like materials via hydrophobic associations without sacrificing the facile injectability of the material. Targeted gelation and mucoadhesion properties can be obtained by the synthesis of polymers with desired PBA and hydrophobic graft contents.</p> / Master of Applied Science (MASc)

The instability mechanism of the shear-thinning and shear-thickening fluids pasta circular cylinder is studied using linear theory. The shear-dependent viscosityis modeled by the Carreau-law where the rheological parameters, the power-index and the material time constant are chosen in the range 0.4 &lt; n &lt; 1.75 and0.1 &lt; λ &lt; 100. A second order finite-difference code is used for the simulationof cylinder flow in which the Immersed Boundary Technique is implemented torepresent the cylinder surface on a Cartesian mesh. The critical Reynolds num-ber for the onset of instability is reported for a range of rheological parameters.Structural sensitivity analysis based on the idea of ”wavemaker” is performedto identify the core of the instability. Perturbation kinetic energy budget is alsoconsidered to examine the physical mechanism of the instability. The charac-teristics of base-flow: drag coefficient, size of recirculation bubble and viscositydistribution are presented to provide useful knowledge about shear-thinning ef-fect in flow past a cylinder.

An investigation has been carried out into the rheology of chocolate in relation to its flow and mixing features in a real industrial environment. The chocolate manufacturing plant of Rowntree at York provided a base for this study. The project aims were: a) to measure the viscous and time dependent properties of chocolate. b) to explain the observed flow properties in relation to the constituents of chocolate. c) to determine the shear rate which, for a given recipe, yields a minimum stable viscosity (of particular commercial value). d) to assess the type of mixer able to provide this duty. The experimental work involved rheological studies with concentric cylinder and tubular viscometers, operated to measure viscosity as a function of shear rate and shearing time. The chocolate samples studied were taken from various points in the manufacture process at Rowntree, York. Model chocolate systems were made from cocoa liquor, and sugar with cocoa butter, which were studied to underpin the basic mechanisms of the flow properties of the total chocolate. Shear thinning in milk chocolate has been shown to be accounted for by surface coating and fat release from the cocoa cellular material. Analysis of the sugar and cocoa butter system gave large hysteresis loops which may be explained as due to agglomeration of the sugar particles. The level of hysteresis was found to be related to the polarity of the liquid phase, such that a more polar fluid results in less hysteresis. Laboratory experiments have revealed that the level of work input to give permanent viscosity reduction for milk chocolate is dependent on the measuring shear rate. The level of optimum shear input for the measuring range 10 to 130 sec 1 is 645 sec for 30 minutes. The apparent viscosity measured at lower shear rates requires much longer ([approx]100 minutes). / Yorkreco, Nester York Ltd.

Defect generation and propagation in thin films, such as separation membranes, can lead to premature or catastrophic failure of devices such as polymer electrolyte membrane fuel cells (PEMFC). It is hypothesized that defects (e.g., air bubbles, pin-holes, and holes) originate during the manufacturing stage, if precise control is not maintained over the coating process, and they propagate during system operation. Experimental and numerical studies were performed to detect and eliminate defects that were induced during slot die coating of high-viscosity (1 to 40 Pa-s), shear-thinning solutions. The effects of fluid properties, geometric parameters and processing conditions on air entrainment and coating windows (limited set of processing conditions for which defect-free coating exists) were studied. When smaller slot gaps and coating gaps were used, relatively small bubbles were entrained in the coated film. The air bubble sizes increased as the viscosity of the coating solution decreased. A semi-empirical model correlating the maximum coating speed to a solution's material properties, geometric parameters and processing conditions was developed. Such a predictive model will enable engineers to determine the maximum coating boundary for shear-thinning and Newtonian solutions within certain constraints. Smaller coating gaps and low-viscosity solutions produced higher coating speeds. The surface tension property of the coating solution provided stability to the coating bead. Therefore, solutions with higher surface tension could be processed at higher coating speeds.

Une étude théorique et expérimentale de la convection de Rayleigh-Bénard pour un fluide non-Newtonien rhéofluidifiant a été effectuée. L’approche théorique consiste en une analyse linéaire et faiblement non linéaire de l’instabilité thermo-convective d’une couche horizontale d’un fluide non-Newtonien, d’étendue supposée infinie dans le plan horizontal, chauffée par le bas et refroidie par le haut. Le comportement rhéofluidifiant est décrit par le modèle de Carreau. Pour ce modèle, les conditions critiques d’instabilité du régime conductif sont les mêmes que pour un fluide Newtonien. L’objectif de l’analyse faiblement non linéaire consiste à déterminer d’une part la valeur critique du degré de rhéofluidification à partir duquel la bifurcation primaire devient sous critique et d’autre part l’influence de rhéofluidification sur la sélection du motif de convection au voisinage des conditions critiques, en tenant compte d’un éventuel glissement à la paroi, d’une conductivité thermique finie de celle-ci et de la thermodépendance de la viscosité. Les conséquences sur le champ de viscosité et l’évolution du nombre de Nusselt sont caractérisées. L’approche expérimentale consiste à visualiser par ombroscopie les motifs de convection qui se développent dans une cellule cylindrique. Deux rapports d’aspect ont été considérés : AR = 3 et AR = 4. Les fluides utilisés sont des solutions aqueuses de Xanthan à différentes concentrations. L’influence du degré de rhéofluidification combiné avec la thermodépendance de la viscosité sur le domaine de stabilité des rouleaux et des hexagones ainsi que sur la zone de transitions rouleaux hexagones est mise en évidence / Theoretical and experimental study of Rayleigh-Bénard convection in a non-Newtonian shear-thinning fluid was performed. The theoretical approach consists in a linear and a weakly nonlinear of thermo-convective instability in a horizontal layer of a non-Newtonian fluid, assumed infinite in extent, heated from below and cooled from above. The rheological behavior of the fluid is described by the Carreau model. For this rheological model, the critical threshold is the same as for a Newtonian fluid. The objective of the weakly non linear analysis is to determine on one hand the critical value of the shear-thinning degree above which the bifurcation becomes subcritical and on the other hand, the influence of shear-thinning effects on the pattern selection near the onset, taking into account the possibility of wall slip, a finite thermal conductivity of the walls as well as the thermo-dependency of the viscosity. The impact on the viscosity field and on the evolution of the Nusselt number are characterized. The experimental approach consists in visualizing the convection patterns using the shadowgraph method in a cylindrical cell. Two aspect ratios were considered : AR = 3 and AR = 4. The fluids used are aqueous solutions of xanthan-gum at different concentrations. The influence of shear-thinning effects combined with the thermo-dependency of the viscosity on the stability domain of rolls and hexagons as well as on the transition between rolls and hexagons is highlighted