Investigation on the effect of temperature on evaporative characteristic length of a porous medium

Abstract

Evaporation from a porous medium goes through three different stages; the physics of drying is completely different in each stage. In the first stage, liquid films maintain high hydraulic conductivity leading to high evaporation rates; it mainly depends on the atmospheric demand. Duration of stage 1 is given in terms of a suitable length scale, Lcap, which originates from the competition between the capillary, gravitational, and viscous forces. It is known that Lcap depends strongly on the particle size and distribution of the pore sizes in a porous medium. We report experiments of evaporation from an initially saturated homogeneous porous medium consisting of nearly mono-disperse (0.70–0.85 mm diameter) glass beads, while heating from above using IR radiation. We found significant changes in Lcap values depending on the incident heat load. We discuss these results based on changes in the fluid properties, such as surface tension and sub-surface temperature gradient. It is expected that such a study would be beneficial not only to the drying industries but also in the agricultural sector and cooling devices.