Interfacial evaporation and evolution in porous media: a study of pillar-array micromodel.

Evaporation in confined pores critically influences natural and industrial systems, from soil salinization to energy-efficient desalination. While conventional models describe evaporation as a two-stage process (constant-rate followed by falling-rate periods), they neglect the dynamic evolution of liquid-vapor interfaces after air invasion, where phase change shifts to intricate pore-scale networks. We hypothesize that pore confinement and interface morphology govern local evaporation rates, allowing further interpretations of macroscale evaporation behavior. Here, we employed pillar-array micromodels as 2D porous media analogs, enabling real-time visualization of interface evolution during evaporation. High-resolution image processing quantified spatial-temporal variations in interfacial areas and curvature, classifying interfaces as external (near the vaporization front) or internal (between vaporization and desaturation fronts). Results revealed that external interfaces dominated phase change (85-92 % contribution), while internal interfaces contributed minimally (<15 %) due to tortuous vapor pathways and reduced humidity gradients. A characteristic interfacial curvature length scale (1-50 μm) dictated evaporation kinetics: intrinsic rates increased exponentially with decreasing curvature radius, demonstrating a near-logarithmic correlation. This framework clarifies the illusion by soil water retention, which predicts capillarity conserved water and suppressed evaporation in smaller pores. By linking interfacial geometry to confinement-enhanced kinetics, our findings establish a mechanistic framework to predict phase change in porous media, with implications for soil hydrology, membrane design, and colloidal systems.