Dissertations / Theses: 'Viscosity'

1

Bronsch, Arne. "Viscosity of slags." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-229196.

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Slags plays a significant role at high temperature processes. The estimation of the slag viscosity is vital for the safe run of e.g. entrained flow gasifiers. One opportunity of determination is rotational viscometry. This technique is disadvantageous in view of elevated temperatures, applied materials and the necessary time. Additionally, the viscosity can be predicted by the help of viscosity models, where viscosity is a function of slag composition and temperature. Due to changing slag properties within the technical processes, the calculated viscosities can hugely differ from measured ones. In this work, the viscosities of 42 slags where measured up to 100 Pa s and temperatures up to 1700 °C. Oxidizing and reducing conditions were applied. Additionally, selected slag samples were quenched at defined temperatures to qualitatively and quantitatively determine the formed minerals by X-ray diffraction (XRD). Differential temperature analysis (DTA) was applied to find the onset of crystallization for the complementation of investigations. The Einstein-Roscoe equation was chosen to improve the classic viscosity models. Reducing atmosphere decreased viscosity and the number of formed minerals was increased. Slags show a shear-thinning behavior above ca. 10 vol.-% of solid mineral matter. Also, Newtonian behavior was observed up to 60 vol.-%. To overcome problems with the kinetic cooling behavior of the slags, a viscosity approximation method was applied afterwards. This can result in optimized viscosity predictions when several preconditions are fulfilled.

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2

Riesch, Christian. "Micromachined viscosity sensors." Aachen Shaker, 2009. http://d-nb.info/997162279/04.

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3

Bukula, Nwabisa Asanda. "Optimisation of clearcoat viscosity." Thesis, Nelson Mandela Metropolitan University, 2016. http://hdl.handle.net/10948/4814.

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Modern automobiles are painted with basecoat, technology which is either metallic, solid colour or pearlescent. This requires protection from chemicals, scratching, weathering and UV light by applying a protective top coat (clearcoat) over the basecoat. For the clearcoat to cure into a hard protective shell it undergoes an irreversible crosslinking process. This usually takes place over the first four to five hours, depending on the formulation and weather conditions. The speed of crosslinking can be enhanced by temperature. Pot life is important as it can affect the overall quality of the painted surface. If crosslinking occurs too quickly, before the clearcoat is applied onto the surface, the clearcoat cannot be used to produce a good quality finish. The “expired” mixture is thus discarded. If used, the quality of the finished product cannot be guaranteed to last, and the paintwork may have to be redone. This often means removing the underlying paint and primer as well with the clearcoat film. Besides the time lost, the discarded clearcoat mixture often lands in the landfill, polluting ground water and the environment. It is thus important from the point of view of both the environment preservation and waste management, that as much clearcoat as possible is used without being wasted. It was proven in an earlier study (BSc Hon Formulation Science Treatise, 2011) that adding eugenol to a clearcoat mixture after crosslinking had started could reduce its viscosity, which is an indicator of crosslinking progress. Crosslinking subsequently resumed at a lower rate than in traditional blends. If stored away from oxygen and high temperatures, this blend could maintain optimum viscosity indefinitely. In this follow up study an optimum formulation was developed using D - optimal experimental design. It sought to extend the pot life to avoid waste to spray painters while saving the environment from pollution. The formulation that gave the desired viscosity after five hours of pot life was adopted. It was hypothesised that the optimum formulated clearcoat mixture would have a longer pot life than its traditional counterparts, and that it would perform just as well as the traditional clearcoat mixtures. To study the rate of crosslinking (disappearance of functional groups and appearance of the urethane bond), FTIR spectrometry was performed on a mixture produced from the optimized formula in comparison to that of a traditional mixture (the control). The rate of disappearance of functional groups was found to be lower in the eugenol mixture than in the control mixture. After six hours, eugenol was added into the control mixture, and this seemed to reduce the viscosity with the re-emergence of functional groups in the mixture. After 24 hours of crosslinking, an FTIR scan was done on the solid sample and this revealed that the eugenol mixture had crosslinked fully, with no detectable functional groups in the sample.

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Chan, Paul Wing Hung. "In-situ viscosity measurement." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341507.

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5

Campanelli, John R. "Interfacial viscosity and emulsion stability." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63776.

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6

Caudwell, Derek Roger. "Viscosity of dense fluid mixtures." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412706.

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7

Hunter, Ian Norman. "The viscosity of gaseous mixtures." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253386.

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8

Riesch, Christian [Verfasser]. "Micromachined Viscosity Sensors / Christian Riesch." Aachen : Shaker, 2009. http://d-nb.info/1159835438/34.

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9

Haberbusch, Diane. "Viscosity Regulation In Polymer Extrusion." Cleveland State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=csu1386782032.

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10

Rothan, Alexandre. "Etude rhéologique de formulations thermodurcissables, pour la modélisation de procédés de type SMC." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE003/document.

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Les travaux présentés s’axent autour de 2 chapitres indépendants : - le 1er concerne l’étude rhéologique d’une formulation pour SMC sans fibres. Cette étude permet d’élaborer des lois de comportement rhéologique. Ces lois sont ensuite insérées dans un code de calcul de simulation numérique afin de prédire les efforts mis en jeu lors d’une compression. Ces données simulées sont comparées avec des données de compression obtenues expérimentalement. - le 2ème se penche sur l’étude d’un comportement rhéologique rare : la rhéopexie négative. La viscosité de l’échantillon dépend de l’histoire de cisaillement qui lui est appliquée. Ce comportement est très sensible à la composition du mélange, et fait intervenir 4 constituants. Dès lors que l’un d’eux est retiré, le phénomène disparaît. Le mélange étudié est constitué de produits classiquement utilisés pour la production de SMC
The research presented is divided into 2 independents chapters: - the 1st one focuses on the rheological study of a fibreless formulation for SMC. This study allows us to write constitutive equations of the formulation. These equations are in turn implemented in a numerical simulation program, in order to predict the forces generated during a compression experiment. These simulated data are eventually compared with experimental data obtained during compression.- the 2nd chapter concerns the study of a rare rheological behaviour: the negative rheopexy. The viscosity of the sample depends on its shear history, in a very different way than a thixotropic sample’s viscosity would. This rheological behaviour is very component sensitive, and results from the interactions between 4 components. As soon as one of them is missing, the negative rheopexy disappears. The mixture studied is constituted of products traditionally used for the production of SMC

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Pleines, Maximilian. "Viscosity-control and prediction of microemulsions." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS139.

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La viscosité est une propriété fondamentale des fluides complexes et qui reste encore difficile à prédire quantitativement. Cette propriété macroscopique provient de propriétés moléculaires et mésoscopiques. La compréhension et l’estimation de l'évolution de la viscosité avec des paramètres variables est important pour plusieurs applications, entre autres pour l’extraction liquide-liquide et pour la formulation de systèmes tensioactifs aqueux.Dans ce travail, un modèle "minimal" prenant en compte les énergies libres mises en jeu a été développé pour aider à comprendre, contrôler et prédire l'évolution de la viscosité des microémulsions en présence de solutés. Le terme «minimal» signifie dans ce contexte que ce modèle est basé sur un ensemble minimal de paramètres qui sont tous mesurables ou ont une signification physique, ce qui permet d’éviter le recours à des paramètres ajustables. Ce modèle développé dans cette thèse considère les termes chimiques à l'échelle moléculaire, les termes physiques à l'échelle mésoscopique ainsi que les caractéristiques d'écoulement à l'échelle macroscopique a été appliqué sur des microémulsions pauvres en eau utilisé pour l’extraction des métaux ainsi que sur des systèmes tensioactifs anioniques aqueux
Viscosity is a fundamental property of complex fluids that is still nowadays extremely difficult to predict quantitatively. This macroscopic property originates from molecular and mesoscopic properties. The understanding and prediction of the evolution of the viscosity with changing parameters is crucial for several applications, amongst others for liquid-liquid extraction processes and for formulation of aqueous surfactant systems.In this work, a “minimal” model taking into account the relevant free energies was developed that helps to understand, control and predict the evolution of the viscosity of microemulsions in presence of solutes. The term “minimal” means in that context that this model is based on a minimal set of parameters that are all measurable and have a physical meaning, thus avoiding input of any adjustable parameter. This model that considers the chemical terms at molecular scale, the physical terms at meso-scale as well as the flow characteristics at macroscale was applied on water-poor extracting microemulsions as well as on aqueous anionic surfactant systems

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Loebker, David W. "Effervescent spraying of high viscosity fluids." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/7041.

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Almotari, Masaed Moti M. "Viscosity and Density of Reference Fluid." Thesis, University of Canterbury. Physics and Astronomy, 2006. http://hdl.handle.net/10092/2065.

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The viscosity and density of bis(8-methylnonyl) benzene-1,2- dicarboxylate {diisodecyl phthalate (DIDP)}, with a nominal viscosity at T = 298 K and p = 0.1 MPa of 87 mPa•s, have been measured at temperatures from (298.15 to 423.15) K and pressures from (0.1 to 70) MPa. A vibrating wire viscometer, with a wire diameter of about 0.15 mm, was utilised for the viscosity measurements and the results have an expanded uncertainty, (k = 2), including the error arising from the pressure measurement, of between ±(2 and 2.5) % The density was determined with two vibrating tube densimeters one for operation at p≈0.1 MPa with an expanded uncertainty (k = 2) of about ±0.1 %, the other that used at pressures up to 70 MPa, with an estimated expanded uncertainty (k = 2) of about ±0.3 %. Measurements of density and viscosity were performed on three samples of DIDP each with different purity stated by the supplier and as a function of water mass fraction. The measured viscosity and density are represented by interpolating expressions with differences between the experimental and calculated values that are comparable with the expanded (k = 2) uncertainties. The obtained viscosities at p = 0.1 MPa agree with values reported in the literature within the combined expanded (k = 2) uncertainties of the measurements while our densities differ by no more than 1.5 %. Viscosity data at p > 0.1 MPa deviate systematically from the literature values in the range of -10 % to 10 %. An apparatus capable of simultaneously measuring the solubility of a gas dissolved in a liquid and the viscosity and the density of the resulting mixture over a wide temperature and pressure range was constructed and tested. Preliminary results have been reported.

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14

Huang, Jin. "Extensional viscosity of dilute polymer solutions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0004/MQ46075.pdf.

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15

Lu, Egang. "Bulk viscosity of a pion gas." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104847.

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In this thesis, we study kinetic theory and chiral perturbation theory, which are employed to compute the bulk viscosity of a gas of pions at temperatures below the QCD crossover temperature, for the physical value of m, to lowest order in chiral perturbation theory. Bulk viscosity is controlled by number-changing processes which become exponentially slow at low temperatures when the pions become exponentially dilute, leading to an exponentially large bulk viscosity ζ ∼ (F^8/m^5)*exp(2m/ T), where F ≃ 93 MeV is the pion decay constant.
La théorie cinématique des particules et la théorie perturbative chirale sont d'abord presentées. Grâce à ces outils, la viscosité volumique d'un gaz de pions à une température en-deçà de la température de transition de phase de la chromodynamique quantique est calculée pour la valeur expérimentale de m, au premier ordre de la théorie perturbative. À basse température, les processus affectant le nombre de particules ralentissent de manière exponentielle lorsque la densité des pions devient exponentiellement faible. Ces processus contrôlent la viscosité volumique, qui à son tour devient exponentiellement large ζ ∼ (F^8/m^5)*exp(2m/T), pour une constante de désintegration des pions F ≃ 93 MeV.

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16

Fan, Jingyun. "Lubricating properties of PMA viscosity modifiers." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445329.

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17

Caswell, Robert J. "Viscosity effects in small diameter hydrocyclones." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278416.

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18

Glen, N. F. "Viscosity coefficient measurement at elevated pressure." Thesis, University of Glasgow, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372405.

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19

Marchant-Lane, Sophie. "Low viscosity nematics : design of dopants." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434117.

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20

GAMA, MARCIA SOARES. "VISCOSITY OF HEAVY FRACTIONS OF OIL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9312@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
Os processos de destilação atmosférica e a vácuo do petróleo têm como sub-produtos mais pesados os resíduos atmosféricos e de vácuo, respectivamente. Modelos encontrados na literatura não descrevem bem a dependência da viscosidade com a temperatura para estas frações. Há grandes diferenças entre valores experimentais e calculados e no comportamento da curva temperatura X viscosidade. As viscosidades dinâmicas de sete diferentes amostras de resíduos foram determinadas experimentalmente. As amostras foram caracterizadas através de ensaios de: densidade, SARA, concentração de asfaltenos e destilação simulada. Com base em suas características físicas são propostos modelos de viscosidade de frações pesadas de petróleo.
Atmospheric and vacuum residua are the heaviest byproducts of the distillation processes. Literature models don't describe well the viscosity dependency on temperature of these fractions. There are large differences between experimental and calculated values and at the temperature X viscosity curve. Dynamic viscosities of seven different samples were experimentally determined. The samples were characterized by: density, SARA, asphalthene concentration and simulated distillation. Based on their physical characteristics, viscosity models for heavy fractions of oil are proposed.

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Al-Awadi, Hameed. "Multiphase characteristics of high viscosity oil." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/13902.

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Heavy oil production has drawn more and more attention in petroleum industry. The amount of heavy oil in the world is twice more than the conventional oil (low viscosity), which has been consumed rapidly from the past. The understanding of flow patterns and pressure losses in multiphase flow with high viscosity oil are vital to assist the design of transportation pipeline. This thesis involves experimental investigation of two phase and three phase flows under high oil viscosity conditions (up to 17000cP) in horizontal pipelines. The multiphase (oil/water/solid/gas) facility was designed and constructed at Cranfield University and consists of 6m long horizontal pipeline of 0.026m diameter along with instrumentations. The principal objectives of the work were to study the effect of viscosity, water cut, temperature variance, and flow conditions on flow patterns and pressure drops for (oil/gas and oil/water) two phase flows; to compare the measured flow parameters and phase distribution with those predicted from models found in the literature for two phase flows; and to conduct an experimental study of gas injection effect on pressure gradient in (oil/water/gas) three phase flow. Due to the nature of heavy oil reservoirs, sand is associated with oil/water mixture when extracted; therefore sand concentration effect on pressure drop in (oil/water/sand) three phase flow is also examined. For oil-air flow, a smooth oil coating was observed in the film region of slug flow, while a ripple structure of oil coating film was found at higher superficial air velocity for slug flow regime and annular flow regime. The ripple structure was believed to increase the effective roughness of the pipe wall, which resulted in higher pressure gradients. The pressure drop correlations from Beggs and Brill (1973) and Dukler et al. (1964) were used to compare with experimental pressure gradients for oil/air flow. It was found that these correlations failed to predict the pressure gradients for heavy oil/air flows in this work. Several new heavy oil/water flow patterns were named and categorized based on observations. Though the heavy oil viscosity is an essential parameter for oil continuous phase flow on pressure drop, it had no significant effect beyond Water Assist Flow (WAF) condition, as a threshold was found for water cut with fixed superficial oil velocity. The transition criterion by McKibben et al. (2000b) for WAF was found to be able to predict this threshold reasonably well. Core Annular Flow (CAF) models were found to greatly under predict the pressure gradients mainly due to the coating (oil fouling) effect associated with this study. A new coating coefficient was introduced to models presented by Bannwart (2001) and Rodriguez et al (2009). The addition of solid in the mixed flow led to minor increase in the pressure gradient when the particles were moving with the flow. However, higher sand concentration in the system led to higher pressure gradient values. The addition of gaseous phase to the oil/water flow was more complex. The gaseous injection was beneficial toward reducing the pressure gradient when introduced in oil continuous phase only at very low water cuts.

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Villeneuve, Randall A. (Randall Alan). "Effects of viscosity on hydrofoil cavitation." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/17325.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1993, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993.
Includes bibliographical references (leaves 118-120).
by Randall A. Villeneuve.
M.S.

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23

Liu, Weian, Yin Yang, and Gang Lu. "Viscosity solutions of fully nonlinear parabolic systems." Universität Potsdam, 2002. http://opus.kobv.de/ubp/volltexte/2008/2621/.

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In this paper, we discuss the viscosity solutions of the weakly coupled systems of fully nonlinear second order degenerate parabolic equations and their Cauchy-Dirichlet problem. We prove the existence, uniqueness and continuity of viscosity solution by combining Perron's method with the technique of coupled solutions. The results here generalize those in [2] and [3].

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Touhami, Youssef. "Effects of viscosity on dynamic interfacial tension." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5607.

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In this study, we have investigated the interfacial tension (IFT)-lowering potential of a range of caustic solutions which were contacted with dilute solution of linoleic acid in light paraffin oil. Two polymers, namely, polyvinyl alcohol and polyacrylamide were added to the caustic solution in order to increase bulk phase viscosity. The dynamic IFT of caustic, polymer and caustic-polymer solutions were measured. By using different linoleic acid concentrations up to 100 mM, it was found that an increase in acid concentration was accompanied by a decrease in IFT for any given caustic composition. When the acid strength was fixed at 10 mM and the caustic concentration was also increased up maximum of 250 mM, the lowest IFT values were obtained at 12.5 mM NaOH. The dilute polymer solutions lowered the IFT of the oleic phase against neutral water from 30.0 to about 15 mN/m. However, the addition of the polymeric material to the caustic solution produced a marginal reduction in dynamic IFT at early contact times and also produced characteristic IFT minima at all caustic concentrations. (Abstract shortened by UMI.)

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Chan, Wendy Wing Yan. "Effect of viscosity on biofilm phenotypic expression." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0015/MQ49603.pdf.

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Burns, Kirstin Anne. "The effective viscosity of ash-laden flows." CONNECT TO THIS TITLE ONLINE, 2007. http://etd.lib.umt.edu/theses/available/etd-05142007-114642/.

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Mihaiescu, Adrian N. "Eddy viscosity turbulence models for compressible mixing." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7982.

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The K - L and K - ϵ turbulence models are used to simulate the turbulent mixing induced by the Rayleigh-Taylor and Richtmyer-Meshkov instabilities. The models contain additional source terms for the turbulence kinetic energy which depend on the type of the instability. A new criterion based on ratio of the averaged flow and turbulence time scales is introduced for differentiating between the two types of instabilities. The original formulation of the turbulence kinetic energy source present in the K - ϵ model is modified in order to accurately capture the evolution of the Richtmyer-Meshkov instability in both heavy/light and light/heavy configurations. Additional constraints are imposed to the models in order to prevent non-physical solutions when strong gradients are present in the flow. Three test problems are considered and the performance of the turbulence models is assessed by comparing their solutions with the results obtained by high resolution Implicit Large Eddy Simulations (ILES). First, the classical Rayleigh-Taylor and Richtmyer-Meshkov problems are solved. A new approach for initializing the turbulence models in proposed for the Rayleigh-Taylor problem. It is found that both turbulence models describe successfully the self similar growth of the Rayleigh-Taylor and Richtmyer-Meshkov instabilities and can predict accurately the spatial distribution of the fluid concentrations and of the turbulent kinetic energy. The last problem involves the mixing induced at two planar interfaces by multiple shock reflections and refractions. The turbulence models estimate correctly the evolution of the mixing and of the total kinetic energy in the mixing zones. The transport equations of the turbulence models are solved numerically and the influence of the numerical schemes on the results is investigated. It is concluded that the numerical schemes do not have an important influence on the results in the case of the classical Rayleigh-Taylor problem (provided that grid convergence has been achieved and the turbulence models have been initialized using the method proposed here). However, in the presence of shocks (such as in the case of the Richtmyer-Meshkov instability), the HLLC Riemann solver should be used together with a reconstruction scheme of third or higher order of accuracy.

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Padrel, de Oliveira Carla Maria Bispo. "Viscosity of liquid hydrocarbons at high pressure." Thesis, Imperial College London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402965.

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Wen, Chien-Hui. "High Birefringence and Low Viscosity Liquid Crystals." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3206.

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In this dissertation, liquid crystal (LC) materials and devices are investigated in order to meet the challenges for photonics and displays applications. We have studied three kinds of liquid crystal materials: positive dielectric anisotropic LCs, negative dielectric anisotropic LCs, and dual- frequency LCs. For the positive dielectric anisotropic LCs, we have developed some high birefringence isothiocyanato tolane LC compounds with birefringence ~0.4, and super high birefringence isothiocyanato biphenyl-bistolane LC compounds with birefringence as high as ~0.7. Moreover, we have studied the photostability of several high birefringence LC compounds, mixtures, and LC alignment layers in order to determine the failure mechanism concerning the lifetime of LC devices. Although cyano and isothiocyanato LC compounds have similar absorption peaks, the isothiocyanato compounds are more stable than their cyano counterparts under the same illumination conditions. This ultraviolet-durable performance of isothiocyanato compounds originates from its molecular structure and the delocalized electron distribution. We have investigated the alignment performance of negative dielectric anisotropic LCs in homeotropic (vertical aligned, VA) LC cell. Some (2,3) laterally difluorinated biphenyls, terphenyls and tolanes are selected for this study. Due to the strong repulsive force between LCs and alignment layer, (2,3) laterally difluorinated terphenyls and tolanes do not align well in a VA cell resulting in a poor contrast ratio for the LC panel. We have developed a novel method to suppress the light leakage at dark state. By doping positive [Delta][epsilon] or non-polar LC compounds/mixtures into the host negative LC mixtures, the repulsive force is reduced and the cell exhibits an excellent dark state. In addition, these dopants increase the birefringence and reduce the viscosity of the host LCs which leads to a faster response time. Dual-frequency liquid crystal exhibits a unique feature that its dielectric anisotropy changes from positive to negative when we increase the operating frequency. Submillisecond response time can be achieved by switching the frequency of a biased voltage, rather than switching the voltage at a given frequency. In this dissertation, we investigate the dielectric heating effect of dual-frequency LCs. Because the absorption peak of imaginary dielectric constant occurs at high frequency region (~ MHz), there is a heat generated when the LC cell is operated at a high frequency voltage. To measure the transient temperature change of the LC inside the cell, we have developed a non-contact method by utilizing the temperature-dependent birefringence property of the LC. Most importantly, we have formulated a new dual-frequency LC mixture which greatly reduces the dielectric heating effect while maintaining good physical properties. Another achievement in this thesis is that we have developed a polarization independent phase modulator by using a negative dielectric anisotropic LC gel. With ~20 % of polymer mixed in the LC host, the LC forms polymer network which, in turn, exerts a strong anchoring force to the neighboring LC molecules. As a result, the operating voltage increases but the response time is significantly decreased. On the phase shift point of view, our homeotropic LC gel has ~0.08 [pi] phase shift, which is 2X larger than the previous nano-sized polymer-dispersed liquid crystal droplets. Moreover, it is free from light scattering and requires a lower operating voltage. In conclusion, this dissertation provides solutions to improve the performance of LC devices both in photonics and displays applications. These will have great impacts in defense and display systems such as optical phased array, LCD TVs, projectors, and LCD monitors.
Ph.D.
Other
Optics and Photonics
Optics

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30

Sansom, Ahmos. "Spreading gravity currents with temperature-dependent viscosity." Thesis, University of Nottingham, 2000. http://eprints.nottingham.ac.uk/14140/.

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The spreading of a fluid under gravity has many important industrial and geophysical applications and has been the focus of much research. Variations in the thermal properties of the fluid have often been neglected. This thesis introduces a series of models incorporating fluids having temperature-dependent viscosity and vertical cross-sectional profile of small aspect ratio to show the important effects that cooling can have on the flow field. The numerical results show features that are commonly observed in experiment and lava dome growth, such as plateauing and fingering.

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31

Dandekar, Abhijit Yeshwant. "Interfacial tension and viscosity of reservoir fluids." Thesis, Heriot-Watt University, 1994. http://hdl.handle.net/10399/1397.

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32

Cook, David J. "The effects of viscosity on flavour perception." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289066.

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33

Hewett, Kylie. "The viscosity behaviour of polymethacrylates in solution." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333562.

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34

Elmes, D. R. "Creep and viscosity in two kaolin clays." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372627.

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35

Sherwood, J. M. "Blood velocity and viscosity in bifurcating microchannels." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1400720/.

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Blood is a complex fluid comprised of predominantly red blood cells (RBCs) suspended in a continuous, Newtonian phase, the plasma. Blood viscosity is highly dependent on the RBC concentration (haematocrit) and also displays shear thinning properties, as a result of RBC deformation and aggregation at high and low shear rates, respectively. However, these two phenomena also lead to uneven haematocrit distributions, which are exacerbated in microvascular bifurcations. In the present study, multifaceted experiments of human blood, perfused through bifurcating microchannels, are used to further elucidate the relationship between haematocrit, velocity and viscosity. A custom pressure based perfusion system was developed and was coupled with image acquisition for velocity measurement with μPIV and further processing. The acquired data was analysed in order to investigate the flow characteristics of human blood in two different idealised bifurcation geometries. The `cell-depleted layer' (CDL), a region of reduced haematocrit which occurs near the walls of the channel, and the continuous haematocrit distribution were experimentally measured. Analytical and numerical approaches were used to extract further information on the effect of flow rate, flow ratio and the presence of aggregation on microhaemodynamics. In the parent branch of the bifurcation, RBC aggregation was observed to increase the radial migration of RBCs away from the vessel wall. This enhanced the non-uniformity of the haematocrit downstream of the bifurcation and altered the relative velocity between the RBCs and the suspending medium. A skewed distribution of cells was observed downstream of the bifurcation, which resulted in skewed velocity profiles, which were also captured in the analytical and computational approaches. The geometry of the bifurcation was observed to influence the results and RBC aggregation quite significantly modified the haemodynamic characteristics even at high flow rates.

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Mohammed, Malami. "Viscosity and density of asymmetric hydrocarbon mixtures." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/42783.

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The main focus of this research has been on providing useful experimental viscosity and density data on some representative asymmetric hydrocarbon mixtures with particular interest on mixtures of higher-molecular-weight aliphatic hydrocarbons with dissolved methane. This thesis details incremental improvements in the design and operation of an existing vibrating-wire viscometer-densimeter (VWVD). These improvements were necessary in order to allow safe investigations of viscosity of highly flammable mixtures such as methane + n-hexadecane. The procedure for absolute viscosity measurement using the VWVD is described in detail. In the absolute mode of operation, the properties of the vibrating-wire (i.e. radius and length) and that of the suspended sinker (i.e. mass and volume) were determined via independent mechanical measurements. The diameter (and hence the radius) of a cetreless-ground tungsten wire was measured accurately using a laser micrometer whereas the length of the wire was carefully measured with an internal caliper. The mass and volume of the suspended sinker were determined via hydrodynamic weighing methods. Simultaneous viscosity and density measurements were made on binary mixtures of n-hexadecane, 2,6,10,15,19,23-hexamethyltetracosane (Squalane) or cyclohexane with dissolved methane each at four different compositions. Measurements were made in the temperature range from (298.15 to 473.15) K, pressure range (0.1 to 200) MPa and methane mole fractions x1 (0 to 0.4) with an overall combined expanded uncertainties within 0.3 % in density and 2 % in viscosity with a coverage factor k = 2. Additional measurements were conducted on perfluoropolyether (also known as krytox® GPL 102) over the same temperature and pressure range. The data generated were successfully correlated for density using the modified Tait equation and for viscosity, by means of the Tait-Andrade equation. These correlations described most of the data to within their expected uncertainties. In an attempt to model the viscosity of the binary mixtures, the extended hard sphere model was tested both in predictive and correlative approaches using different mixing rules. Surprisingly, in the predictive mode, the results indicated that, the conventional linear mole-fraction average rule provided a better prediction with a maximum absolute deviations (ΔMAD,ηs) in viscosity ranging from (9 to 64)% compared to the quadratic and the other more complicated combining rules such as the Van der Waals rules. This was observed consistently across all the three binary systems investigated in this work. In the correlative mode however, the maximum absolute deviations were in the range from (3 to 33) % when the molar core volumes of each mixture composition were treated as adjustable parameters with the higher ΔMAD,ηs mostly observed in the mixtures of methane + squalane. Furthermore, the performance of the extended hard sphere scheme and the Vesovic-Wakeham (VW) model in predicting the viscosity of asymmetric mixtures were tested. This was done by comparing the predicted results from both models against the experimental data obtained in this work. In this regard, three performance indicators namely: the maximum absolute deviations (ΔMAD,η); the average absolute deviations (ΔAAD,η) and the average bias (Δbias,η) of these models were compared. It was found that the VW model consistently produced lower values of all these quantities for the two binary systems investigated. For example, for the mixture of methane + n-hexadecane the ΔMAD,ηs obtained from the VW model range from (10 to 31)%, whereas those of the extended hard sphere model range from (10 to 47)%. On the basis of our analysis, the VW model seems to be more promising and therefore more likely to be recommended for predicting the viscosity of asymmetric mixtures. Finally, the results obtained from this project extend our knowledge and basic understanding of the viscosity characteristics of the so-called asymmetric mixtures especially to higher temperatures and pressures.

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Tshehla, Maashutha Samuel. "Two dimensional flow of variable viscosity fluids." Doctoral thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/4936.

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Lloyd, Wennie Lim. "Viscosity and lyophoresis of comminuted tomato products /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487263399025573.

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Patel, Vijay. "Studies of magnetic viscosity in anisotropic materials." Thesis, Keele University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261526.

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Holtzinger, Jennifer. "Influence of viscosity modifiers on hydrodynamic friction." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10222.

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Polymer additives, named Viscosity Modifiers (VMs), have been added to motor engine lubricants for more than 50 years, where they are used to increase the viscosity index of their blends. It is well known that solutions of VMs exhibit shear thinning under high strain rate conditions as are present in engine journal bearings. In the past, this shear thinning was regarded as undesirable since it might reduce hydrodynamic film thickness. However it has been reported that multigrade oils containing VMs provide lower engine friction than polymer-free oils of comparable viscosity and the most likely origin of this is a reduction of hydrodynamic friction due to temporary shear thinning of the polymer solutions. In this thesis, the role of polymer shear thinning in reducing hydrodynamic friction is clarified by the experimental work carried out on a range of different polymer types. This study includes the viscosity measurements over a wide range of shear rate and also friction and film thickness analyses performed in a soft elastohydrodynamic lubrication contact in order to avoid piezoviscous effects. A very recent technique based on laser induced fluorescence technology is used to evaluate the film thickness. These experimental results are compared with theoretical calculations, which allows based on the rheological data of each polymer solution, the impact of polymer shear thinning on hydrodynamic friction to be quantified. The studied polymer solutions show a decrease in film thickness and in hydrodynamic friction compared to Newtonian fluids of similar viscosity. This reduction is ascribed to the temporary shear thinning of polymer blends. The proposed theoretical models show good agreement with the experimental values. They appear to be useful tools to quantify the impact of polymer shear thinning on film thickness and friction. In addition to this main work, the polymer solutions are analysed under high contact pressure and the shear stability of some commercials viscosity modifiers are studied. A new method is developed to quantify the permanent viscosity loss of each polymer solution and this is compared to the industrial Kurt-Orbahn test.

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Miller, James. "Modelling melt viscosity for nuclear waste glass." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/9110/.

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This work forms part of a Collaborative Awards in Science and Engineering industrial studentship (iCASE), jointly funded by the Engineering and Physical Sciences Research Council and the National Nuclear Laboratory. The aim is to develop improved models for calculating viscosities of vitreous nuclear waste melts, particularly with respect to the variation in temperature and composition. Both in vitro and in situ experimentation on nuclear material is complicated by radioactivity and its associated expenses, so computational modelling is the principal means we use to study these industrially important glasses. The problem is approached with both top-down and bottom-up methods. From a more fundamental perspective, beginning in Section 7 Molecular Dynamics techniques are used to simulate glass melts at atomic resolution. An audit of literature forcefields, using a systematic methodology for particulate systems generation, involved calculation of structural and diffusive properties to reveal the advantages and disadvantages of contemporary sodium-borosilicate models. After developing an improved glass model, from Section 11 different methods of viscosity computation were trialled to determine that most appropriate for the conditions of the nuclear glass melters. In Section 14 the Inoue2 SBN forcefield was combined with the Green-Kubo technique, using simulated runtimes more than double those of previous literature work. The analyses produced qualitative agreement in compositional and temperature trends, as well as order-of-magnitude quantitative agreement between experimental and computational viscosity results for ternary nuclear glass frits. Complimentary top-down approaches were also used, with rotary viscometry experimentation employed in Section 4 to gather temperature-composition-viscometry data for nuclear waste glasses. These data were used with different fitting algorithms in Section 15 to compare the efficacy of theoretical descriptions for glass viscosity, described in Section 3. A combination of fitting techniques assembles in Section 17 an interpolative second-order model for which the maximum discrepancy between prediction and experiment is 17% of the absolute viscosity.

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Benlahmar, Ouidad. "Dispersant viscosity improvers for lubricating oil compositions." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/34518.

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Dispersant viscosity modifiers (DVMs) are multi-functional lubricant additives combining in one additive composition, dispersancy and the ability to improve the viscosity of a lubricant, at high engine temperatures, sufficiently to maintain efficient lubrication. Compounds useful for this purpose are characterized by a polar group attached to a relatively high molecular weight hydrocarbon chain. Polymeric compounds that were studied for possible use as DVMs were maleated ethylene–propylene copolymers and copolymers containing an alkyl methacrylate and vinyl amine-containing monomers. The current method used by Lubrizol to prepare grafted polar monomers onto saturated polymers is a solvent-based chemical route, which involves precipitation, filtration, drying and then dissolution in base oil. Because of those drawbacks, an alternative synthesis needs to be found to get a much more cost-effective product. Therefore, the main objectives of this research were to apply melt techniques to replace the solvent-based free radical grafting reaction and to optimise the grafting level without product detriment.

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Khaleque, Tania Sharmin. "Strongly variable viscosity flows in mantle convection." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:851f7069-8164-4499-8afa-5a06141c5911.

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Convection in the Earth's mantle is a complicated phenomenon that causes various tectonic activities and affects mantle evolution on geologic time scales (billions of years). It is a subject as yet not fully understood. The early success of the high Rayleigh number constant viscosity theory was later tempered by the absence of plate motion when the viscosity is more realistically strongly temperature dependent. A similar problem arises if the equally strong pressure dependence of viscosity is considered, since the classical isothermal core convection theory would then imply a strongly variable mantle viscosity, which is inconsistent with results from postglacial rebound studies. We consider a mathematical model for Rayleigh-Bénard convection in a basally heated layer of a fluid whose viscosity depends strongly on both temperature and pressure, defined in an Arrhenius form. The model is solved numerically for extremely large viscosity variations across a unit aspect ratio cell, and steady solutions are obtained. To improve the efficiency of numerical computation, we introduce a modified viscosity law with a low temperature cut-off. We demonstrate that this simplification results in markedly improved numerical convergence without compromising accuracy. Continued numerical experiments suggest that narrow cells are preferred at extreme viscosity contrasts. We are then able to determine the asymptotic structure of the solution, and it agrees well with the numerical results. Beneath a stagnant lid, there is a vigorous convection in the upper part of the cell, and a more sluggish, higher viscosity flow in the lower part of the cell. We then offer some comments on the meaning and interpretation of these results for planetary mantle convection.

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Reid, Joshua. "Angelic Viscosity: Dali and Dante in Paradise." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etsu-works/2864.

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Kulchanyavivat, Sawin. "The effective approach for predicting viscosity of saturated and undersaturated reservoir oil." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3168.

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Predicting reservoir oil viscosity with numerical correlation equations using field-measured variables is widely used in the petroleum industry. Most published correlation equations, however, have never profoundly realized the genuine relationship between the reservoir oil viscosity and other field-measured parameters. Using the proposed systematic strategy is an effective solution for achieving a high performance correlation equation of reservoir oil viscosity. The proposed strategy begins with creating a large database of pressure-volumetemperature (PVT) reports and screening all possible erroneous data. The relationship between the oil viscosity and other field-measured parameters is intensively analyzed by using theoretical and empirical approaches to determine the influential parameters for correlating reservoir oil viscosity equations. The alternating conditional expectation (ACE) algorithm is applied for correlating saturated and undersaturated oil viscosity equations. The precision of field-measured PVT data is inspected by a data reconciliation technique in order to clarify the correctness of oil viscosity correlations. Finally, the performance of the proposed oil viscosity correlation equations is represented in terms of statistical error analysis functions. The result of this study shows that reservoir oil density turns out to be the most effective parameter for correlating both saturated and undersaturated reservoir oil viscosity equations. Expected errors in laboratory-measured oil viscosity are the main factors that degrade the efficiency of oil viscosity correlation equations. The proposed correlation equations provide a reasonable estimate of reservoir oil viscosity; and their superior performance is more reliable than that of published correlation equations at any reservoir conditions.

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Isasa, Jean-David. "Optimisation des propriétés diélectriques de copolymères à base de PVDF : étude de la formulation d’encres et optimisation de procédés d’impression." Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0026.

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Les polymères fluorés fortement polaires tels que le P(VDF-TrFE) sont des matériaux émer-gents dans le domaine de l'électronique organique flexible en raison de leurs nombreuses appli-cations en tant qu'actionneurs, capteurs ou récupérateurs d'énergie. En raison de la forte polarité des liaisons C-F, une orientation dipolaire coopérative dans les domaines cristallins peut être in-duite et est principalement responsable des propriétés électroactives de ces polymères. Le dépôt de ces matériaux en films minces peut être réalisé par impression ou déposition par voie liquide, offrant une méthode de mise en oeuvre polyvalente et évolutive pour la production de couches hautement fonctionnelles. Néanmoins, la mise en oeuvre de telles couches dans des dispositifs pratiques est directement liée aux propriétés rhéologiques des encres électroactives qui déter-minent les régimes d'impression conduisant à des couches électroactives stables et fonction-nelles. Dans cette étude, nous avons évalué le comportement viscoélastique de solutions de P(VDF-TrFE) et P(VDF-TrFE-CTFE) pour des solvants de polarité différente, allant du régime dilué au régime concentré. À partir de ces mesures, nous avons extrait, en utilisant une approche basée sur des lois d’échelles, plusieurs paramètres polymère-solvant fortement dépendants de la com-position du polymère et de la polarité du solvant. Des mesures complémentaires de diffusion de la lumière ont également corrélé les changements de conformation du polymère avec l'affinité polymère-solvant extraite de l'analyse rhéologique. Enfin, nous avons examiné l'impact de la for-mulation des encres sur la fabrication de dispositifs organiques à base de PVDF par la méthode de sérigraphie afin d'établir une corrélation entre les paramètres rhéologiques de l'encre et la résistance au claquage par court circuits pendant les cycles de polarisation. Ainsi, cette étude fournit une compréhension approfondie de l'influence de la solvatation du polymère sur les ré-gimes d'impression afin d'obtenir des couches électroactives de haute performance
Highly polar fluorinated polymers such as P(VDF-TrFE) are emerging materials in the field of flex-ible organic electronics because of their numerous applications as actuators, sensors, or energy harvesters. Due to the high polarity of C-F bonds, cooperative dipole orientation in crystalline domains can be induced and are primarily responsible for the electroactive properties of these polymers. The processing of these materials into thin films can be performed by solution printing or casting, offering a versatile and scalable method for the production of highly functional layers. Nevertheless, the implementation of such layers in practical devices is directly related to the rhe-ological properties of the electroactive inks that determine the printability regimes leading to stable and functional electroactive layers.In this study, we evaluated the viscoelastic behavior of P(VDF-TrFE) and P(VDF-TrFE-CTFE) solu-tions for solvents of different polarity, ranging from the dilute to the concentrated regime. From these measurements, we extracted using a scaling approach several polymer-solvent parameters that are highly dependent on the polymer composition and solvent polarity. Complementary light scattering measurements further correlated the polymer conformational changes with the poly-mer-solvent affinity extracted from the rheological analysis. Finally, we examined the impact of the ink formulation on the fabrication of PVDF-based organic devices by the screen-printing method in order to establish a correlation between the rheological parameters of the ink and the resistance to breakdown during the polarization cycles. Therefore, this study provides a deeper understanding on the influence of the polymer solvation on the printability regimes in order to obtain high performance electroactive layers

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Wu, Liushun. "Study on some phenomena of slag in steelmaking process." Doctoral thesis, KTH, Mikro-modellering, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32740.

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The present work is to study slag phenomena in steelmaking process. In order to attain thegoal, a number of high temperature experiments and simulation experiments were carried out. Four master slags were used to study the effect of CaF2 on slag viscosity. Experimentalresults indicated the effect of CaF2 on slag viscosity depended strongly on the composition ofmaster slag. For high basicity slags, CaF2 mainly suppressed the precipitation of solid phasesat lower temperatures, leading to a lower viscosity compared to CaF2-free slags. For slagswith higher SiO2 contents, CaF2 both lowered the viscosity of the liquid phase and suppressedthe precipitation of solid phases. The viscosities of solid-liquid mixtures were experimentally determined for silicon oilparaffinsystem at room temperature and solid-liquid oxide mixture at steelmakingtemperature. The results of both measurements indicated that the increasing trend of mixturesviscosity with particle fraction can be described by Einstein-Roscoe equation.Silicone oils of different viscosities were used to simulate slag foaming. The experimentalresults showed, at a constant viscosity, the foaming height increased first with superficialvelocity before reaching a maximum value. Thereafter, the foaming height decreased with thefurther increase of the superficial velocity. Similar, a maximum foaming height was observedat an optimum viscosity when a constant superficial gas velocity was applied. Based on theexperimental data, a semi-empirical equation of foaming height was developed. Thepredictions of the model agreed well with experiment data. The model could also reasonablywell explain the industrial pilot trial experiments. Water-silicon oils model and liquid alloy (Ga-In-Sn)- 12% HCl acid model were employed tosimulate the formation of open-eyes in a gas stirred ladle. The experimental results indicatedthat the viscosity of the top liquid and the interfacial tension between the two liquids had onlylittle effect on the open-eye size. A semi-empirical model was developed to describe the sizeof open-eye as functions of the gas flow rate, bath height and slag height. The two sets ofparameters obtained for the water and Ga-In-Sn models were very different. Industrial trialswere also conducted to examine the applicability of the models. Liquid alloy model couldwell predict the formation of an open-eye during ladle treatment. Two cold models, sodium tungstate-oil model and water-oil model, were carried out tosimulate the formation of droplets in a gas stirred ladle. The experimental results showed thatthe gas flow rate and interfacial tension had strong impact on the size of droplets. A semiempiricalmodel was developed to describe the size of droplets for water model. Meanwhile,the parameter obtained for water model can be used for sodium tungstate-silicone oil system.The results indicate the model has strong compatibility.
QC 20110419

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Kondratiev, Alex. "Development of viscosity models for multiphase slag system /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18306.pdf.

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Meller, Mika. "Dispersive mixing of high viscosity ratio polymer blends /." Lausanne, 2000. http://library.epfl.ch/theses/?nr=2267.

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Viscardy, Sébastien. "Viscosity and microscopic chaos: the Helfand-moment approach." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210964.

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Depuis les premiers développements de la physique statistique réalisés au 19ème siècle, nombreux ont été les travaux dédiés à la relation entre les processus macroscopiques em>irréversibles(tels que les phénomènes de transport) et les propriétés de la dynamique réversible des atomes et des molécules. Depuis deux décennies, l'hypothèse du chaos microscopique nous en apporte une plus grande compréhension. Dans cette thèse, nous nous intéressons plus particulièrement aux propriétés de viscosité.

Dans ce travail, nous considérons des systèmes périodiques de particules en interaction. Nous proposons une nouvelle méthode de calcul de la viscosité valable pour tous systèmes périodiques, quel que soit le potentiel d'interaction considéré. Cette méthode est basée sur la formule dérivée par Helfand exprimant la viscosité en fonction de la variance du moment de Helfand croissant linéairement dans le temps.

Dans les années nonante, il a été démontré qu'un système composé de seulement deux particules présente déjà de la viscosité. Les deux disques durs interagissent en collisions élastiques dans un domaine carré ou hexagonal avec des conditions aux bords périodiques. Nous appliquons notre méthode de calcul des propriétés de viscosité dans les deux réseaux. Nous donnons également une explication qualitative des résultats obtenus.

L'étude de la relation entre les propriétés de viscosité et les grandeurs du chaos microscopique représente l'une des principales tâches de cette thèse. Dans ce contexte, le formalisme du taux d'échappement joue un rôle majeur. Ce formalisme établit une relation directe entre cette grandeur et la viscosité. Nous étudions numériquement cette relation et la comparaison avec les résultats obtenus par notre méthode sont excellents.

D'autre part, le formalisme du taux d'échappement suppose l'existence d'un répulseur fractal. Après avoir mis en évidence son existence, nous appliquons le formalisme proposant une formule exprimant la viscosité en termes de l'exposant de Lyapunov du système (mesurant le caractère chaotique de la dynamique)et de la dimension fractale du répulseur. L'étude numérique de cette relation dans le modèle à deux disques durs est réalisée avec succès et sont en excellent accord avec les relations obtenus précédemment.

Enfin, nous nous penchons sur les systèmes composés de N disques durs ou sphères dures. Après une étude de l'équation d'état et des propriétés chaotiques, nous avons exploré les propriétés de viscosité dans ces systèmes. Les données numériques obtenues sont en très bon accord avec les prévisions théoriques d'Enskog. D'autre part, nous avons utilisé notre méthode de calcul de la viscosité dans des systèmes de Lennard-Jones. De plus, nous avons proposé une méthode analogue pour le calcul numérique de la conduction thermique. Nos résultats sont en très bon accord avec ceux obtenus par la méthode de Green-Kubo.

In this thesis, we first devote a section on the history of the concept of irreversibility; of the hydrodynamics, branch of physics in which the viscosity appears; of the kinetic theory of gases establishing relationships between the microscopic dynamics and macroscopic processes like viscosity; and, finally, the interest brought in statistical mechanics of irreversible processes by the theory of chaos, more precisely, the microscopic chaos. We propose a method based on the Helfand moment in order to calculate the viscosity properties in systems of particles with periodic boundary conditions. We apply this method to the simplest system in which viscosity already exists: the two-hard-disk model. The escape-rate formalism, establishing a direct relation between chaotic quantities of the microscopic dynamics (e.g. Lyapunov exponents, fractal dimensions, etc.), is applied in this system. The results are in excellent agreement with those obtained by our Helfand-moment method. We extend the calculation of the viscosity properties to systems with more than two hard balls. Finally, we compute viscosity as well as thermal conductivity thanks to our own method also based on the Helfand moment.

Doctorat en sciences, Spécialisation physique
info:eu-repo/semantics/nonPublished

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Dissertations / Theses on the topic 'Viscosity'

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