Visualization of wicking and drying of a granular bed with a perforated plate

In this study, we experimentally examine capillary-driven imbibition and the subsequent drying process of a polymer granular bed originally developed for water purifier and humidifier systems. The bed is composed of polystyrene-divinylbenzene spheres, with a perforated plate inserted at different heights, and a constant water supply applied to the bed. Using a high-speed recording at 2,000 fps, we captured the temporal progression of the wetting front, water bypassing through the plate orifices, and drying patterns. Quantitative data such as front velocity, the size and location of local voids, rising motion of the voids, and the realignment of granular bed were extracted using image processing techniques. We find that the inclusion of perforated plate increases flow resistance and plays a role of additional confining wall, resulting in more uniform capillary imbibition and saturation. In contrast, the drying kinetics remain unaffected by the plate. These suggest that, by tuning perforated plate geometry-such as hole size and spacing-one can achieve consistent fluid distribution across beds of varying composition. Future studies may explore the effect of various configuration of plates such as its numbers and orientation, particle sizes, and inclined beds to further understand liquid transport and drying behavior.