Characterization of Confined Water Evaporation in Porous Media

While phase change materials have been widely used for latent heat storage, water/ice is promising for cold energy storage due to its large latent heat. Characterizing phase change, either ice melting or water evaporation, within porous media is of great significance for efficient cold energy charging/discharging and enhanced energy storage, but it remains challenging because of the opaque nature of porous matrix. In this work, by combining the non-destructive NMR-MRI technology and pore-scale numerical simulation, we investigate the dynamics of water-vapor transition in porous medium with an average grain size of 150 μm. The transient water content and distribution are obtained from NMR transversal relaxation time T₂. The shifting of T₂ curve and MRI imaging results show uniform evaporation over the entire device, which implies cavitation-induced evaporation in homogenous porous medium. This is further elucidated from the COMSOL simulation, where we look into the water-vapor interface evolution during the evaporation process in a representative pore. Our insights on water phase change in porous media are also valuable to geothermal energy extraction.