Heat and mass transfer, particularly water transport was investigated at pore scale in unconsolidated porous media with a thermal probe as a heater. A CCD camera combined with a microscope was employed to observe and record water morphology variation during heating. The water near the heater firstly evaporated and then diffused to the region relatively far away where it condensed. As local temperature increased, the water would evaporate again and diffuse to even farther region. Even though the temperature and ambient conditions were the same, it could be induced that the liquid might have different chemical potentials with different interface curvatures. The chemical potential relationship between liquid and its surrounding vapor determined the phase change direction. At certain conditions, liquid evaporation and vapor condensation can coexist at the same region.

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