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Séminaire Andreas YIOTIS le 21 octobre

14 octobre 2011

Pore-Scale modeling of transport processes in porous media guided by experimental studies ; Drying and NAPL dynamics

21 octobre à 14h
Amphithéâtre Nougaro
Andreas YIOTIS, post-doc au FAST

Résumé :
We discuss the application of two pore scale methods for the modeling of transport processes in porous media ; Pore Network and Lattice Boltzmann modelling for the problems of drying and Non-Aqueous Phase Liquids Dynamics, respectively.

For the case of drying, we perform a series of experiments with glass bead packings saturated by liquid hexane in predominantly 2D glass cells under environmental conditions to study the dynamics of the drying process and identify the major transport mechanisms. Our experimental setup allows for the monitoring of the bulk liquid and gas phase distribution patterns, as well as the liquid films that form at the pore walls after the invasion of the bulk gas phase. We are thus able to classify the drying pore space into 3 distinct regions ; a far-field completely-wet region, where the pore space is saturated by the bulk liquid hexane ; a completely dry region, close to side of the medium open to the ambient environment, that contains only hexane vapors ; and finally an intermediate region, located between the first two, that is partially saturated by liquid hexane in the form of liquid films at the walls of the pores and by hexane vapors in the central part of the pore space.
Based on our experimental results we propose a pore network model that accounts for the major transport mechanisms within the porous medium coupled with mass transfer by diffusion through a mass boundary layer over the external surface of the medium. We show that in the limit of a gravity-stabilized percolation front (interface between the completely-wet and film regions) the medium can be treated as a 1D continuum where analytical solutions to the governing equations are derived. We are thus able to obtain results for the drying rates, the critical saturation and the extent of the film region with respect to the various dimensionless numbers that describe the process ; the Bond number, a film-based Capillary number and the dimensionless extent of the mass boundary layer.