Evaporation from porous media is of significant importance in many disciplines ranging from hydrology and agriculture, to food sciences and powder technology. Within the Chair of Geohydroinformatics, we are interested in the environmental relevance of this process with a particular focus on the investigation of soil water evaporation dynamics under a variety of boundary conditions. Soil water evaporation involves coupled heat and mass flow and depends on the transport properties of soil and the external atmospheric conditions. We employ a wide range of numerical and experimental tools to delineate effects of many parameters such as particle size distribution, wettability, structure of porous media, and the external conditions (e.g. wind, radiation, relative humidity and ambient temperature) on the soil water evaporation dynamics.
Figure caption. The conceptual sketch illustrating the jump of the liquid meniscus from the surface and formation of the secondary drying front. (a) Detachment of the liquid meniscus from the surface and pinning to a level below during the transition from stage-1 to stage-2 evaporation. (b) Formation of the secondary drying front at the onset of stage 2. The evaporation is preceded by the capillary flow up to the secondary drying front, vaporization at that level, and vapor diffusion through the dry layer. The depth of the secondary drying front at the onset of stage 2 is related to the maximum tail of the interface between the wet and dry zone (see more details in Shokri and Or (2011), Water Resour. Res., 47, W09513).
Figure caption. Liquid phase distribution during evaporation from a sand column obtained by synchrotron x-ray tomography. The arrangement of sand grains and liquid phase within the first scanned block (3.3 x 3.3 x 1.7 mm3) is shown for five time steps. Isolated liquid clusters were filtered out to highlight continuous liquid phase only (see more details in Shokri et al. (2010), Phys. Rev. E, 81, 046308).
Figure caption. Characteristic length (drying front depth) for the transition from stage 1 to stage 2 of drying from partially wettable porous media. Solid line corresponds to the prediction from our model, and the points indicate the depth of the front at the transition measured in the lab. Inserted black and white images correspond to the picture of sand columns at the transition used to determine experimentally the depth of the drying front (see more details in Shokri et al. (2009), Water Resour. Res., 45, W02415).