Improving drying performance of porous media by controlling surface pore size in convective drying

In convective drying of porous media, water evaporates from surface pores exposed to hot air, while capillary pressure drives liquid transport from the interior. Since capillary pressure depends on pore structure, controlling surface pore size can significantly influence drying performance. This study examines the impact of surface pore size on drying efficiency in convective conditions. Experiments were conducted using spherical glass beads of different diameters to analyze moisture distribution and drying behavior. The results show that reducing surface pore size enhances drying rates by maintaining high liquid saturation at the surface. However, excessively small pores increase viscous resistance, limiting water transport to the surface and accelerating the transition to the falling drying rate period, ultimately reducing drying efficiency. The findings suggest that an intermediate surface pore size can minimize drying time by balancing liquid retention and transport. To validate this approach, we tested drying efficiency on common textiles using porous sheets with tailored pores, achieving a drying time reduction of approximately 30%. This study provides deeper insights into drying mechanisms in heterogeneous porous media and offers practical strategies for energy-efficient drying using porous sheets with controlled pore structures.