Post-harvest losses of agricultural products remain a significant challenge in semi-arid regions such as Chad, where high ambient temperatures and limited preservation technologies considerably reduce food availability and quality. Solar drying has emerged as a sustainable and energy-efficient method for preserving fruits and vegetables by reducing moisture content and inhibiting microbial growth. This study investigates the thermal performance and drying behavior of an indirect natural-convection solar dryer under the climatic conditions of N’Djamena. The experimental setup consists of a flat-plate solar air collector coupled with a drying chamber equipped with multiple trays. Key parameters—including solar radiation, ambient temperature, air velocity, relative humidity, and product mass—were continuously monitored throughout the drying process. The thermal efficiency of the solar dryer, the evolution of moisture content, and the drying kinetics of okra were evaluated. Thin-layer drying behavior was analyzed using the Page model to describe the variation of moisture ratio with drying time. Experimental results indicate that the solar dryer achieved temperatures ranging from 50？C to 65？C, significantly exceeding the ambient temperature (34？C - 42？C). Under these conditions, the moisture content of fresh okra decreased from 80% to approximately 6% within 8–10 hours, whereas traditional open-sun drying required 2 - 3 days to reach comparable moisture levels. The thermal efficiency of the system varied between 25% and 40%, depending on solar radiation intensity and airflow conditions. These results demonstrate that natural-convection solar dryers can substantially reduce drying time, enhance product quality, and minimize contamination risks. Consequently, this technology represents a practical and sustainable solution for reducing post-harvest losses and improving food preservation in semi-arid regions such as Chad.
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