Experimental investigation of water distribution in a two-phase zone during gravity-dominated evaporation

摘要

We characterize the water repartition within the partially saturated (two-phase) zone (PSZ) during evaporationfrom mixed wettable porous media by controlling the wettability of glass beads, their sizes, and as well thesurrounding relative humidity. Here, capillary numbers are low and under these conditions, the percolating frontis stabilized by gravity. Using experimental and numerical analyses, we find that the PSZ saturation decreaseswith the Bond number, where packing of smaller particles have higher saturation values than packing made oflarger particles. Results also reveal that the extent (height) of the PSZ, as well as water saturation in the PSZ, bothincrease with wettability. We also numerically calculate the saturation exclusively contained in connected liquidfilms and results show that values are less than the expected PSZ saturation. These results strongly reflect thatthe two-phase zone is not solely made up of connected capillary networks but also made of disconnected waterclusters or pockets.Moreover, we also find that global saturation (PSZ+full wet zone) decreases with wettability,confirming that greater quantity of water is lost via evaporation with increasing hydrophilicity. These results showthat connected liquid films are favored in more-hydrophilic systems while disconnected water pockets are favoredin less-hydrophilic systems.