Evaporation from layered porous media

Evaporation rates from porous media may vary considerably due to changes in internal transport mechanisms and potential interruption of hydraulic continuity; both are influenced by media pore space properties. Evaporation behavior in layered porous media is affected by thickness and sequence of layering and capillary characteristics of each layer. We propose a composite characteristic length for predicting drying front depth at the end of a period with a high and constant drying rate (stage 1 evaporation) from layered porous media. The model was tested in laboratory experiments using Hele-Shaw cells filled with alternating layers of coarse and fine sands considering different combinations of thicknesses and positions. The presence of textural interfaces affects drying rate, modifies liquid phase configuration, and affects the dynamics of the receding drying front. Neutron radiography measurements were used to delineate dynamics of liquid phase distribution with high temporal and spatial resolution. Results show that air invading an interface between fine and coarse sand layers results in a capillary pressure jump and subsequent relaxation that significantly modify liquid phase distribution compared with evaporation from homogeneous porous media. Insights are potentially useful for designing mulching strategies and capillary barriers aimed at reducing evaporative losses. Copyright © 2010 by the American Geophysical Union.