Experimental study of the low-pressure-vaporization of water in different porous media

The present study aims to evaluate the benefits of using porous media (PM) to enhance the rate of the low-pressure-vaporization (LPV) of water. An experimental characterization of the process of low-pressure-vaporization (LPV) of water is presented considering four different types of porous media and different initial conditions. This characterization involves the measurement of the time evolution of the porous media temperature and of the total and the vapor pressure inside the vaporization chamber, as well as the indirect determination of the saturation pressure, the mass of water vaporized, its specific rate of vaporization and of the energy removed by this phenomenon. A direct comparison between the evolution of the LPV of water in porous media and the LPV of free water was also made for two selected situations. The results show that the evolution of the LPV parameters, namely the temperature decrease and the rate of energy removal, are strongly dependent on the volume of the water initially contained in the porous medium which in turn, depends essentially of the medium microstructure. The significant differences found between the evolution of the LPV parameters in free water and in porous media are related to different boiling onset mechanisms, which is strongly dependent on the surface tension of the liquid water in the whole LPV process in PM. The practical result of these effects is an increased vaporization rate and an enhanced surface heat transfer capability that justify the use of porous media in a wide variety of applications.