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

Abstract

How spatially organized mixed wettability controls pore-scale interface recession and liquid replenishment during convective drying remains insufficiently understood. This study investigates this process using an established multicomponent pseudopotential lattice Boltzmann model with a cascaded collision operator and a virtual-density wetting treatment. The model is validated against the one-dimensional isothermal Stefan problem, curved surface wetting tests, and a microfluidic evaporation benchmark. At a fixed porosity, hydrophobic small particles are introduced into a hydrophilic framework to form random, enriched, V-shaped, and gradient arrangements, which are examined under different convection intensities and wettability contrasts. A two-term exponential model quantifies the characteristic time scales, fast-stage contribution, residual water mass, and total evaporable water mass. The results reveal distinct but coupled effects of the wettability, convection, and spatial organization. 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.