Short time correlation analysis in porous medium

The study of the mechanical and physico-chemical properties of porous media containing water is of great interest in particular during the phase change. Some thermodynamic models may provide relatively good understanding of this problem but these models are complex because of space averaging differential equations. To check the results obtained with the models, we have developed an acoustic system which monitors the phase change interface over time. The medium used to model the porous medium is a stacking of glass spheres whose diameters are fixed and large compared with the ultrasonic wavelength and whose spaces are filled with water (or ice). Because of spheres induced speckle, the water-ice interface cannot be seen a priori. In order to evidence this interface we have used a method based on correlation similar to the short time Fourier analysis. The result thus obtained shows that the water-ice interface can then be seen clearly. The speed measurements of the ultrasonic wave in porous medium obtained with this method agree with Blot's theory. The preliminary experimental results show a good agreement with the semi-analytical solution.