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

1. General Introduction
The Ludwig-Soret effect, also known as thermal diffusion (or thermal diffusion and also
thermo-migration), is a classic example of coupled heat and mass transport in which the
motion of the particles in a fluid mixture is driven by a heat flux coming from a thermal
gradient. Generally, heaviest particle moves from hot to cold, but the reverse is also seen
under some conditions. The Soret effect has been studied for about 150 years with more
active periods following economic interests (separation of isotopes in the 30s, petroleum
engineering in the 90s ...). Many researchers have developed different techniques to
measure this effect and deduced theories to explain it. However, because of the complexity
of this coupled phenomenon, only recently, there has been an agreement on the values of
the thermal diffusion coefficients measured by different techniques. Theoretically, there
exists a rigorous approach based on the kinetic gas theory which explains the thermal
diffusion effect for binary and multi-component ideal gas mixtures. For liquids, the
theories developed are not enough accurate and there is still a lack of understanding on the
basis of the effect for these mixtures. The situation becomes even more complicated when
considering porous media. Fluid and flow problems in porous media have attracted the
attention of industrialists, engineers and scientists from varying disciplines, such as
chemical, environmental, and mechanical engineering, geothermal physics and food
science. The main goal of the present thesis is to understand this complexity in porous
media when there is a coupling between heat and mass transfer. The main objective is to
study if the effective thermal diffusion depends on the following
• the void fraction of the phases and the structure of the solid matrix, i.e., the extent
of the continuity of the solid phase,
• the thermal conductivity of each phase, i.e., the relative magnitude of thermal
conductivity ratio,
• the contact between the no-consolidated particles, i.e., the solid surface coatings,
• the fluid velocity, i.e., dispersion and free convection in pore spaces.
The background and main goal of this thesis is presented in this chapter.
In chapter 2 we present a theoretical approach based on the volume averaging method to
determine the effective transport coefficients in porous media. In this part, we are
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