Thermodiffusion is one of the mechanisms in transport phenomena in which molecules are transported in a multicomponent mixture driven by temperature gradients. Thermodiffusion in associating mixtures presents a larger degree of complexity than non-associating mixtures, since the direction of flow in associating mixtures may change with variations in composition and temperature. In this study a new activation energy model is proposed for predicting the ratio of evaporation energy to activation energy. The new model has been implemented for prediction of thermodiffusion for acetone-water, ethanol-water and isopropanol-water mixtures. In particular, a sign change in the thermodiffusion factor for associating mixtures has been predicted, which is a major step forward in modeling of thermodiffusion for associating mixtures. In addition, a new model for the prediction of thermodiffusion coefficients for linear chain hydrocarbon binary mixtures is proposed using the theory of irreversible thermodynamics and a kinetics approach. The model predicts the net amount of heat transported based on an available volume for each molecule. This model has been found to be the most reliable and represents a significant improvement over the earlier models. Also a new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. This approach is based on a free volume theory which explains the diffusivity in diffusion-limited systems. The proposed model combined with the Shukla and Firoozabadi model has been applied to predict the Soret coefficient for binary mixtures of toluene and n-hexane, and benzene and n-heptane. Comparisons of theoretical results with experimental data show a good agreement. The proposed model has also been applied to estimate thermodiffusion coefficients of binary mixtures of n-butane & carbon dioxide and n-dodecane & carbon dioxide at different temperature. The results have also been incorporated into CFD software FLUENT for 3-dimensional simulations of thermodiffusion and convection in porous media. The predictions show the thermodiffuison phenomenon is dominant at low permeabilities (0.0001 to 0.01), but as the permeability increases convection plays an important role in establishing a concentration distribution. Finally, the activation energy in Eyring’s viscosity theory is examined for associating mixtures. Several methods are used to estimate the activation energy of pure components and then extended to mixtures of linear hydrocarbon chains. The activation energy model based on alternative forms of Eyring’s viscosity theory is implemented to estimate the thermodiffusion coefficient for hydrocarbon binary mixtures. Comparisons of theoretical results with the available thermodiffusion coefficient data have shown a good performance of the activation energy model.

Thermodiffusion is one of the mechanisms in transport phenomena in which molecules are transported in a multicomponent mixture driven by temperature gradients. Thermodiffusion in associating mixtures presents a larger degree of complexity than non-associating mixtures, since the direction of flow in associating mixtures may change with variations in composition and temperature. In this study a new activation energy model is proposed for predicting the ratio of evaporation energy to activation energy. The new model has been implemented for prediction of thermodiffusion for acetone-water, ethanol-water and isopropanol-water mixtures. In particular, a sign change in the thermodiffusion factor for associating mixtures has been predicted, which is a major step forward in modeling of thermodiffusion for associating mixtures. In addition, a new model for the prediction of thermodiffusion coefficients for linear chain hydrocarbon binary mixtures is proposed using the theory of irreversible thermodynamics and a kinetics approach. The model predicts the net amount of heat transported based on an available volume for each molecule. This model has been found to be the most reliable and represents a significant improvement over the earlier models. Also a new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. This approach is based on a free volume theory which explains the diffusivity in diffusion-limited systems. The proposed model combined with the Shukla and Firoozabadi model has been applied to predict the Soret coefficient for binary mixtures of toluene and n-hexane, and benzene and n-heptane. Comparisons of theoretical results with experimental data show a good agreement. The proposed model has also been applied to estimate thermodiffusion coefficients of binary mixtures of n-butane & carbon dioxide and n-dodecane & carbon dioxide at different temperature. The results have also been incorporated into CFD software FLUENT for 3-dimensional simulations of thermodiffusion and convection in porous media. The predictions show the thermodiffuison phenomenon is dominant at low permeabilities (0.0001 to 0.01), but as the permeability increases convection plays an important role in establishing a concentration distribution. Finally, the activation energy in Eyring’s viscosity theory is examined for associating mixtures. Several methods are used to estimate the activation energy of pure components and then extended to mixtures of linear hydrocarbon chains. The activation energy model based on alternative forms of Eyring’s viscosity theory is implemented to estimate the thermodiffusion coefficient for hydrocarbon binary mixtures. Comparisons of theoretical results with the available thermodiffusion coefficient data have shown a good performance of the activation energy model.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23388号 / 工博第4880号 / 新制||工||1763(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 三浦 清貴, 教授 田中 勝久, 教授 藤田 晃司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Diese Arbeit stützt sich auf die theoretische und experimentelle Untersuchung der Thermodiffusion im Magnetfeld. Bei magnetischen Flüssigkeiten als kolloidalen Suspensionen versteht man unter der Thermodiffusion einen durch einen Temperaturgradienten angestoßenen unidirektionalen Partikeltransport, der zur Separation des Fluids führt. Beschrieben wird die Thermodiffusion theoretisch über das Konzentrationsprofil der Partikel in Abhängigkeit von Zeit und Ort in einer Fluidschicht. Die Experimente detektieren die Separation des Fluids über die Konzentrationsdifferenz zwischen zwei Fluidkammern. Die Bestimmung des Soret-Koeffizienten erfolgt über einen Datenfit zwischen experimentellen und theoretischen Daten. Für das kerosinbasierte Ferrofluid EMG905 wurden zwei Effekte festgestellt. Bei kleinen Magnetfeldstärken wandern die Partikel zum kalten Rand der Schicht (ST>0), bei steigenden Feldstärken kehrt sich diese Richtung um (ST<0). Die Ergebnisse der Untersuchungen zur Thermodiffusion gehen dann in eine lineare Stabilitätsanalyse einer Ferrofluidschicht bei anliegendem Temperaturgradienten und Magnetfeld ein. Dabei wird festgestellt, dass die kritische Rayleigh-Zahl als charakteristische Größe zum Einsetzen von Konvektion von dem Soret-Koeffizienten abhängt. Ist letzterer positiv, wird das Einsetzen von Konvektion begünstigt, ist er wiederum negativ, so kann Konvektion vollständig unterdrückt werden.

Diese Arbeit stützt sich auf die theoretische und experimentelle Untersuchung der Thermodiffusion im Magnetfeld. Bei magnetischen Flüssigkeiten als kolloidalen Suspensionen versteht man unter der Thermodiffusion einen durch einen Temperaturgradienten angestoßenen unidirektionalen Partikeltransport, der zur Separation des Fluids führt. Beschrieben wird die Thermodiffusion theoretisch über das Konzentrationsprofil der Partikel in Abhängigkeit von Zeit und Ort in einer Fluidschicht. Die Experimente detektieren die Separation des Fluids über die Konzentrationsdifferenz zwischen zwei Fluidkammern. Die Bestimmung des Soret-Koeffizienten erfolgt über einen Datenfit zwischen experimentellen und theoretischen Daten. Für das kerosinbasierte Ferrofluid EMG905 wurden zwei Effekte festgestellt. Bei kleinen Magnetfeldstärken wandern die Partikel zum kalten Rand der Schicht (ST>0), bei steigenden Feldstärken kehrt sich diese Richtung um (ST<0). Die Ergebnisse der Untersuchungen zur Thermodiffusion gehen dann in eine lineare Stabilitätsanalyse einer Ferrofluidschicht bei anliegendem Temperaturgradienten und Magnetfeld ein. Dabei wird festgestellt, dass die kritische Rayleigh-Zahl als charakteristische Größe zum Einsetzen von Konvektion von dem Soret-Koeffizienten abhängt. Ist letzterer positiv, wird das Einsetzen von Konvektion begünstigt, ist er wiederum negativ, so kann Konvektion vollständig unterdrückt werden.

On étudie l'évolution d'une solution initialement homogène constituée de deux espèces soumises à un gradient thermique qui génère un transfert de matière, ce qui peut conduire à la séparation des espèces du fluide binaire. La configuration choisie pour étudier la séparation est une cellule rectangulaire (ou parallélépipédique), horizontale et placée dans le champ de pesanteur. La présence d'une source piézo-électrique, sur l'une des parois verticales de la cavité, permet de générer un écoulement stationnaire à grande échelle. L'écoulement est induit par la propagation d'ondes ultrasonores au sein du fluide visqueux : la dissipation de l'énergie acoustique de l'onde au sein du fluide porte le nom d'Eckart streaming. On cherche à optimiser la séparation en combinant gradient thermique et source acoustique. La première partie consiste en l'étude de l'écoulement isotherme généré par l'onde ultrasonore dans un fluide mono-constituant. Après avoir calculé le champ d'intensité acoustique avec l'intégrale de Rayleigh, le profil est implémenté dans un code aux éléments finis Comsol Multiphysics. Les résultats numériques sont comparés avec des résultats expérimentaux antérieurs. Dans une seconde partie, on considère une cavité contenant un fluide binaire. On détermine analytiquement, à l'aide du logiciel Maple, la séparation (différence de fraction massique entre les deux extrémités de la cellule) en fonction des paramètres de contrôle du problème. Des simulations numériques 2D et 3D ont montré un bon accord entre les résultats analytiques et numériques, pour un paramètre acoustique constant et un chauffage par le bas ou par le haut de la cellule. Le problème considéré dépend alors de huit paramètres adimensionnels. Trois d'entre eux sont propres à la nature du fluide binaire : le nombre de Lewis Le, de Prandtl Pr et le facteur de séparation ψ. Il y a ensuite deux paramètres de contrôle, le nombre de Rayleigh thermique Ra et la force acoustique adimensionnelle A. Enfin, les autres paramètres adimensionnels sont les deux rapports d'aspect de la cavité, ainsi que l'épaisseur relative du faisceau acoustique / The evolution of an initially homogeneous solution consisting of two species subjected to a thermal gradient which generates a mass transfer, which can lead to the separation species from the binary fluid, is studied. The configuration chosen to study the separation is a rectangular (or parallelepipedic) cell, horizontal and placed in the gravitational field. The presence of a piezoelectric source on one of the vertical walls of the cavity makes it possible to generate a stationary flow on a large scale. The flow is induced by the propagation of ultra-sonic waves within the viscous fluid : the dissipation of the acoustic energy of the wave within the fluid is called Eckart streaming. We seek to optimize the separation by combining thermal gradient and acoustic source. The first part consists of the study of the isothermal flow generated by the ultrasonic wave in a monoconstituent fluid. After calculating the acoustic intensity field with the Rayleigh integral, the profile is implemented in a Comsol Multiphysics finite element code. The numerical results are compared with previous experimental results. In a second part, we consider a cavity containing a binary fluid. A configuration heated from the top is privilegied to allow the insertion of an acoustic source. The separation (difference of mass fraction between the two ends of the cell) is determined analytically using the Maple software as a function of the control parameters of the problem. 2D and 3D numerical simulations showed a good agreement between the analytical and numerical results, for a constant acoustic parameter. The problem considered depends on eight dimensionless parameters. Three of them are specific to the nature of the binary fluid : the Lewis number Le, the Prandtl number Pr and the separation factor ψ. There are then two control parameters, the thermal Rayleigh number Ra and the adimensional acoustic force A. Finally, the other dimensionless parameters are the two aspect ratios of the cavity, as well as the relative thickness of the beam.

A fundamental step in the further developments of comprehensive modelling of the diffusive processes in liquids requires the possibility of obtaining reliable and accurate experimental data of the diffusion and thermodiffusion coefficients of multicomponent liquid systems. In the present work, we perform an experimental investigation of the diffusive properties of binary and ternary liquid systems. Two experimental techniques, the ‘Open Ended Capillary’ technique and the ‘Transient Interferometric Technique’ have been developed. Those techniques have been used for the experimental characterization of several systems composed of 1,2, 3,4-Tetrahydrnaphtalene, Isobutylbenzene and Dodecane at ambient temperature. Those particular species were selected as a simplified multicomponent system modelling the fluids contained in natural crude oils reservoirs. <p>For each of these techniques, experimental set-ups were designed, implemented and calibrated. The procedures for identifying the ternary diffusion coefficients from the measured compositions fields were studied in details. <p>The Open Ended Capillary Technique was applied under gravity condition to study isothermal diffusion binary and ternary systems. Difficulties related to a new procedure for interpreting the data collected at short times of the experiments are highlighted and its implication in the generalization of the technique for the study of multicomponent systems is discussed.<p>The Transient Interferometric Technique was used to perform an experimental study of three binary systems under gravity conditions. It was also applied for the investigation of ternary systems under microgravity condition in the frame of the DSC on SODI experiment, which took place aboard the International Space Station in 2011. The experimental results are reported and the analysis of the accuracy of the technique is presented. The TIT is the first technique ever providing accurate experimental measurements of the complete set of diffusion and thermodiffusion coefficients for ternary liquid systems.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

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Le comportement d’un fluide confiné dans un milieu poreux peu perméable (micro- and méso-pores) a été étudié en ce qui concerne ses propriétés de diffusion de masse, de conductivité thermique et de thermodiffusion. Pour ce faire des simulations de dynamique moléculaire hors équilibre ont été réalisées sur des mélanges binaires modèles placés dans des conditions thermodynamiques diverses, confinés dans des milieux poreux de géométrie lamellaire de différentes natures (lisse ou atomique, plus ou moins adsorbant) en utilisant l’ensemble __//_ et l’ensemble grand canonique. Les résultats ont montré que les effets du milieu poreux sur les propriétés de transport sont d’autant plus marqués que lataille de pore est petite, que l’adsorption est forte et que la température est basse. Les résultats ont permis d’évaluer quantitativement ces effets. Il a aussi été montré que la rugosité des murs a un impact très important sur le coefficient de diffusion de masse et non négligeable sur celui de thermodiffusion. / The aim of this work was to study how a fluid confined in a low permeability porous medium (micro- and meso-porous) behaves concerning its properties of mass diffusion, thermal conductivity and thermal diffusion. For this purpose, non-equilibrium molecular dynamics simulations have been performed on simple binary mixtures placed in various thermodynamic conditions, confined in a porous medium of lamellar geometry of different types (structure-less or atomistic, more or less adsorbent) in __//_ and grand canonical ensembles. The results show that the effects of porous medium on transport properties are more pronounced when the pore size is small, the adsorption is strong and the temperature is low. The results allowed to evaluate these effects quantitatively. In addition, it has been found that the wall roughness has a major impact on the mass diffusion coefficient and a non negligible one on the thermal diffusion coefficient.