On the mechanism of evaporation of water from a nonhygroscopic porous medium

The behavior of evaporation of water and its salt solution from a nonhygroscopic porous medium is investigated experimentally in this study. Quartz sand (30-50mesh) was packed as the porous medium. Pure water with electric resistance greater than 10 M Omega and solution with various concentrations of sodium sulfate were used in the experiments. The inducted air was heated by electric light radiation and the temperature was controlled by a PID controller. The now velocity of inlet air was controlled by adjusting the electric fan. The experimental results show that the existence of salt has a great influence on the rate of surface evaporation. The drop of vapor pressure of water by the addition of salt is considered to be only an minor factor. The inhibition of the evaporation of microlayer, driven by the gradient of the disjoining pressure is suggested to be an important factor in this system.