Experimental measurement of the effective diffusion and thermodiffusion coefficients for binary gas mixture in porous media

Thermodiffusion or Soret effect, corresponding to a mass flux caused by a temperature gradient applied to fluid mixture, has been taken into account in many porous media applications, particularly in chemical engineering and geophysics. In the literature, the effective macro-scale diffusion coefficients are now well established, while uncertainty remains concerning the relationship between the effective thermodiffusion coefficient and micro-scale parameters (such as pore-scale geometry). Our previous study on theoretical model of effective thermodiffusion coefficient for a pure diffusion regime confirmed that the tortuosity factor acts in the same way on both Fick diffusion coefficient and on thermodiffusion coefficient. In this study, new experimental results obtained with a two bulb apparatus are presented. The diffusion and thermodiffusion of a helium-nitrogen and helium-carbon dioxide system through cylindrical samples filed with glass spheres of different diameter are measured at the atmospheric pressure. Concentrations are determined by analyzing the gas mixture composition in the bulbs with a katharometer device. A transient-state method for coupled evaluation of thermodiffusion and Fick coefficient in two bulbs system is proposed. The obtained results are in good agreement with theoretical results from previous study and emphasize the porosity of the medium influence on both diffusion and thermodiffusion process. The tortuosity of the medium calculated using both effective diffusion and effective thermodiffusion coefficients are the same. (C) 2010 Elsevier Ltd. All rights reserved.