Geometry-controlled enhancement of convective heat transfer and moisture diffusion during passive solar drying

This study investigated whether the passive solar drying performance of Perionyx excavatus could be improved through geometry-based tray modification without increasing solar-energy input or using auxiliary airflow. The novelty lies in the integrated evaluation of tray curvature, tray elevation, and drying-surface type on drying kinetics, solar drying efficiency ( η ), specific energy consumption ( SEC ), apparent effective moisture diffusivity ( D eff ), and shrinkage behavior under open-field passive solar conditions. A 2 × 2 × 5 full-factorial experiment was conducted using two surface types, two mesh geometries, and five tray elevations. Drying occurred predominantly in the falling-rate regime, suggesting that internal moisture migration was important, although external vapor-removal conditions may also have influenced the early drying stage. The apparent D eff ranged from 7.605 × 10 −11 to 8.773 × 10 −11 m 2 s −1 . The arched mesh trays elevated to 75 cm exhibited the most favorable drying performance, consistent with improved lower-surface exposure and vapor-release pathways; however, airflow velocity, boundary-layer thickness, and local heat-transfer coefficients were not directly measured. The best treatment reduced drying time to 6.0 h, achieved a maximum η of 30.04%, and produced a minimum SEC of 8.01 MJ kg −1 water evaporated. The 75 cm elevation was the best-performing height under the present tray size, sample loading, surface condition, and weather conditions, while 100 cm provided only marginal additional benefit. Overall, simple tray-geometry modification improved macroscopic passive solar drying performance without auxiliary energy input, but the proposed heat- and mass-transfer mechanisms should be interpreted as performance-based evidence rather than direct mechanistic proof.