Determination of the Tortuosity of a Porous Medium by Means of A Thermodiffusion Cell

摘要

We present a technique for determining the value of the tortuosity of a porous medium by performing a separation experiment in a thermodiffusion cell. A temperature difference is applied to a binary mixture while its refractive index is measured by means of a Mach-Zehnder interferometry. The refractive index shows a fast change due to the thermal gradient and a slower one due to the separation induced by the Soret effect. Thus we are able to deduce the mass diffusion coefficient of the sample within the porous medium. By knowing the value of the diffusion coefficient in the free medium and the simple relation between the two values D~* = D/τ~2 , we can calculate the tortuosity of the porous medium. Experimental trials on two distinct samples show a good agreement within the two measured values, but also that the diffusion in a volume which is partly free and partly filled with a porous medium is not theoretically described by our formula.