Séminaire de Mécanique d'Orsay

Le Mercredi 4 juillet à 14h00 - Salle de conférences du FAST

Interfacial Processes Controlling Drying of Porous Media

Nima Shokri
Department of Earth and Environment, Boston University

Drying of porous media is strongly influenced by the interplay between transport properties of the medium and external boundary conditions. Initial stages of evaporation are supported by capillary-induced liquid flow connecting a receding drying front (i.e. the interface between saturated and unsaturated zone) to evaporation surface, the so-called stage-1 evaporation. At a certain drying front depth, gravity overcomes capillary forces and a transition from liquid flow-supported stage-1 to diffusion-supported stage-2 evaporation occurs. Characteristics lengths deduced from transport properties of porous media are proposed to predict the end of stage-1 evaporation under different boundary conditions. Effects of pore size distribution, wettability and structure of porous media are considered in the proposed characteristics lengths. The model predictions are checked and evaluated by a complete series of micro- and macro-scale evaporation experiments using cutting-edge techniques such as synchrotron x-ray tomography and neutron radiography. Results indicate, that the common notion of hydraulic conductivity controlling evaporation rate from porous media is incomplete and other factors may play a role. Besides, new insights regarding dynamics of drying front displacement and preferential flows affected by texture, wettability and structural heterogeneity of drying porous media are discussed.