Modeling, environmental and economic analysis of drying of orange slice in an automatic indirect mixed mode solar dryer.

This study presents an indirect mixed-mode solar dryer (IMMSD) integrated with a photovoltaic system with an automatic, temperature-responsive control system that automatically switches between natural and forced convection, enhancing efficiency and reducing energy use. Unlike previous fixed systems, it prevents over-drying and spoilage. The cost-effective, solar-powered design suits off-grid communities. By integrating drying kinetics with economic and environmental assessments, the system supports sustainability goals. The study also examines how slice thicknesses and tray positions within the drying room affect orange drying kinetics. Then, the IMMSD was used to dry orange slices under real conditions at Aswan University, Egypt, in January 2025, aiming to evaluate performance across different slice thicknesses (4, 6, and 8 mm) and tray positions (lower, middle, and upper levels). The results demonstrated that orange slices with a 4 mm thickness dried on the lower tray reached the final moisture content (MC) more quickly than thicker slices (8 mm) dried on the middle and upper trays. The 4 mm slices achieved the lowest final MC at approximately 12.5%, with a 48% reduction in drying time compared to 8 mm slices on the upper tray. The effective moisture diffusivity (D