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Étude théorique et numérique de l'effet Soret

Abstract : Thermal diffusion, or Soret effect, occurs when a mixture is subjected to a thermal gradient. Mole fractions gradients appears along the thermal gradient as a response of the system. As a non equilibrium phenomenum thermal diffusion is associated to a specified transport coefficient, the Soret coefficient. Its sign indicates the direction of the separation (if negative the corresponding species tend to go preferentially to the cold side) while its modulus value is characteristic of the separation. Although Soret effect has a full theoretical description in the gas phase from the kinetic theory it remains highly not understood in dense media. This work presents the main importance of molecular interactions in the prediction of the Soret effect. First we propose a physical picture of thermal diffusion from non equilibrium molecular dynamics simulations based on results on Lennard-Jones mixtures in which cross interactions were changed from the well known Lorentz Berthelot mixing rules. A macroscopic thermodynamic study of excess properties allows us to link this microscopic picture to the dominating importance of partial molar enthalpies in the understanding of interaction effects. We qualitatively generalised this approach on a typical associated mixture: water ethanol. The last part of the work is dedicated to a generalisation of Prigogine's model (also partly presented by Wirtz and rewritten by Drickamer). We could represent the Soret effect as an activated process with a non constant temperature. This simple model was quantitatively validated on several mixtures and we also predict a new result on the water ethanol mixture at higher temperature but not experimentally tested yet. About this last system we were able to predict the molar fraction at which the Soret coefficient vanishes with a precision of 1%.
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https://tel.archives-ouvertes.fr/tel-00528058
Contributor : Pierre-Arnaud Artola Connect in order to contact the contributor
Submitted on : Thursday, October 21, 2010 - 9:07:51 AM
Last modification on : Saturday, June 25, 2022 - 10:01:54 PM
Long-term archiving on: : Saturday, January 22, 2011 - 2:43:10 AM

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  • HAL Id : tel-00528058, version 2

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Pierre-Arnaud Artola. Étude théorique et numérique de l'effet Soret. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Paris Sud - Paris XI, 2009. Français. ⟨tel-00528058v2⟩

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