Performance evaluation of a reflector-assisted evacuated tube solar dryer for drying banana, mango, and sweet potato

Post-harvest losses of agricultural products due to ineffective drying methods remain a significant challenge in many developing regions, especially in rural, off-grid areas with limited infrastructure access. This study investigates the performance of an indirect solar drying system that utilizes an evacuated tube solar air heater (ETSAH) with a bottom reflector to enhance energy efficiency and improve the quality of dried agricultural products. Experiments were conducted in Kafrelsheikh, Egypt, under natural climatic conditions, using banana, mango, and sweet potato as test crops. The system was evaluated in terms of thermal performance, drying kinetics, energy and exergy efficiency, and economic feasibility. Results showed that the ETSAH system increased air temperature by up to 23.7 °C above ambient, with outlet temperatures exceeding 65 °C during peak hours. Sweet potato achieved the highest thermal and exergetic performance, while banana showed the best economic outcome, with a drying cost of $8.78/kg and an 82.1 % cost saving over market value. Exergy efficiency remained above 35 %, and drying efficiencies ranged from 31 % to 45 %. Overall, the ETSAH-reflector system demonstrated strong technical and economic viability as a clean, low-cost solution for decentralized agricultural drying, offering a sustainable alternative to conventional methods.