Pore-Scale Investigation of Convective Drying in Porous Media: Effects of Mixed Wettability and Structural Heterogeneity

Stronger convection enhances early surface drying, but may accelerate near-surface depletion and strengthen diffusion-limited, late-stage evaporation. Moderate hydrophobicity provides the best balance between the front mobility and hydraulic connectivity in the baseline structure. Convection primarily changes the relative contributions of the fast and slow stages, whereas hydrophobic domain placement determines whether liquid-replenishment pathways remain connected to the receding interface.

The bottom-enriched distribution gives the highest evaporation fraction, the upward-gradient distribution exhibits the best operating condition stability, and the upward V-shaped distribution offers the best compromise between efficiency and robustness. Thus, drying performance depends not simply on the hydrophobic fraction or average wettability, but on the spatial relationship among mixed-wet domains, connected hydrophilic pathways, and the receding interface.

These findings provide pore-scale guidance for gas diffusion layers, porous evaporators, and related phase change transport systems.