Water evaporation from porous media by Dynamic Vapor Sorption

Evaporation from porous media is a subject of growing interest in view of its industrial relevance and of the different spatial scales involved in the problem. A common, yet not fully elucidated feature of evaporation from porous media is the presence of a constant drying rate phase (CDP), which is followed by a falling drying rate phase (FDP). Here, we use a cotton fabric as a model porous medium and study the effects of salts and surfactants on CDP and FDP of aqueous solutions by using the Dynamic Vapor Sorption (DVS) technique. The cotton samples were first characterized by adsorption/desorption isotherms. Then the drying process of fabrics soaked in distilled water and in aqueous solutions at different hardness was investigated. The same procedure was used to study the drying of a dilute surfactant aqueous solution. All these experiments show that the presence of salts and surfactants in water affects the CDP, but not the FDP. At variance with the bulk behavior, an increase of the CDP drying rate was found for the surfactant solution and for aqueous salt solutions up to some hardness value. (C) 2014 Elsevier B.V. All rights reserved.