Influence of climatic conditions on evaporation in soil samples

Abstract

Evaporation rates can be successfully modelled for soil–atmosphere interaction problems by means of a convective vapour flux at the soil surface equal to the product of a driving force (difference between the vapour density at the soil surface and that of the surroundings) and a mass transfer coefficient characterising the resistance of a boundary layer where the transfers take place. While the vapour density at the soil surface can be deduced from solving the coupled heat and moisture transfer equations for the soil below the surface, the determination of the mass transfer coefficients under varying weather conditions is rarely investigated. Laboratory-scale drying tests are performed on a compacted silt specimen, focusing on the influence of atmospheric conditions (relative humidity and wind speed) on the evaporation kinetics and the mass transfer coefficient. Two experimental techniques are used and compared: a drying chamber with relative humidity controlled through saline solutions and a convective microdryer. New insights are given into the prediction of mass transfer coefficients from mass transfer theories. Finally, the results highlight the necessity of testing specimens that are large enough to define relevant mass transfer coefficients for geotechnical applications.