9 - Thermodiffusion in porous media

Abstract

The thermal diffusion process, also known as the Soret effect, is the tendency of a convection-free mixture to separate under a temperature gradient. In general, Soret coefficient is evaluated based on the differentiation in a cell. Especially when the Soret coefficient is negative, such an evaluation is an extremely delicate process. Several ground-based techniques are developed to measure the Soret coefficient. Two techniques are commonly used for binary mixtures with high melting points. The first is the long capillary technique where the samples are processed in capillary tubes placed in a gradient furnace. The liquid vein is then quenched once a steady-state separation is attained. The second is the shear cell technique where there is a superposition of discs with veins running through them. The chapter discusses the complication of a thermal diffusion process in porous media. A detailed literature review provides a variety of techniques for the measurement of Soret coefficient. Subsequently, it discusses the mathematical and numerical methods for the simulation of the Soret effect in both free and porous media. Followed by the introduction of fundamental equations of thermal diffusion and equations used for porous media, the chapter explains the numerical solution technique that allows these equations to be solved. With these techniques, the thermal diffusion process for various cases, namely square and rectangular porous cavities, are then simulated, and the effect of the convection on thermal diffusion is further discussed.