r - Les thèses en ligne de l'INP - Institut National Polytechnique de ...

• a good agreement has been found between macro-scale resolutions and micro-
scale, direct simulations, which validates the proposed theoretical model,
• thermal diffusion modifies the local concentration and this modification depends
locally on the porosity, thermal conductivity ratio and fluid velocity. Therefore, we
cannot ignore this effect.
A new experimental setup has been designed and made-up to determine directly the
effective diffusion and thermal diffusion coefficients for binary mixtures. This setup is a
closed system, which helped carry out the experiments for the case of pure diffusion only.
The experiments have been performed with special all-glass two-bulb apparatus,
containing two double-spherical layers. The diffusion and thermal diffusion of heliumnitrogen
and helium-carbon dioxide systems through cylindrical samples first without
porous media and then filled with spheres of different diameters and thermal conductivities
were measured at the atmospheric pressure. Concentrations were determined by analysing
the gas mixture composition in the bulbs with a katharometer device. A transient-state
method for coupled evaluation of thermal diffusion and Fick coefficient in two bulbs
systems has been proposed. Here, with a simple thermal diffusion experiment, this model
is able to determine both diffusion and thermal diffusion coefficients. The determination of
diffusion and thermal diffusion coefficients is done by a curve fitting of the temporal
experimental results with the transient-state solution describing the mass balance between
the two bulbs. The results showed
• a dependency of the thermal diffusion and diffusion coefficients on the porosity,
• a good agreement with theoretical results, which confirm the validity of the
theoretical results for pure diffusion,
• the tortuosity of the medium calculated using both effective diffusion and effective
thermal diffusion coefficients were not different to the measurement accuracy,
• the experimental results also showed that the particle-particle touching has not a
significant influence on the effective thermal diffusion coefficients.
There is still much work to be done concerning thermal diffusion in porous media. Several
perspectives can be proposed. The following ones present especial interest
• in the theoretical part of this study we developed a coupled heat and mass transfer
macro-scale equation with a non-thermal equilibrium case (using a two-equation
temperature problem). One may use this model when the assumption of thermal
equilibrium is not valid. However, the closure problems have not been solved for
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