Effect of tray elevation and cassava load on solar drying performance, energy efficiency, and drying kinetics

This study evaluates the effects of tray elevation and cassava chip load density on solar drying performance, energy efficiency, and drying kinetics under natural sun-drying conditions in Northeastern Thailand. A full factorial experimental design was applied using three surface load densities (16, 32, and 48 kg m⁻²) and four tray elevations (0, 30, 60, and 90 cm). Drying time, thermal efficiency ( η ), specific energy consumption ( SEC ), and effective moisture diffusivity ( D e f f ) were analyzed. Statistical significance was assessed at a probability level of p < 0.05. The results indicate that tray elevation and load density significantly affected drying time, η, and SEC ( p < 0.0001). The optimal configuration—30 cm tray elevation with a load density of 48 kg m⁻²—reduced drying time by 26%, increased thermal efficiency by 36%, and decreased SEC by 27% compared with conventional ground-level drying. Drying kinetics analysis showed that the Midilli model best described moisture ratio behavior, yielding coefficients of determination ( R² ) greater than 0.99 and the lowest root mean square error ( RMSE ). D e f f increased with tray elevation, ranging from 1.36 × 10⁻⁵ to 1.08 × 10⁻⁴ m² h⁻¹, reflecting enhanced internal mass transfer associated with improved natural convection. Overall, tray elevation is shown to be a simple yet effective passive modification that substantially improves solar drying performance without auxiliary energy input or complex dryer systems. This approach provides a cost-effective, scalable, and energy-efficient alternative to traditional open sun drying and hybrid solar dryers, supporting low-carbon postharvest processing in tropical agricultural systems.