Experimental Study of the Thermal Performance of An Indirect Solar Dryer with Unglazed Collectors Equipped with Three Parabolic Trough Reflectors

The preservation of agri-food products is a major challenge in reducing post-harvest losses, which are a major cause of food insecurity worldwide. Drying is an effective preservation technique, ensuring a longer shelf life for products. Given the concerns related to the costs of drying with fossil fuels and environmental pollution, the use of renewable energy is imperative. Burkina Faso benefits from more than 3,000 hours of sunshine per year, according to statistics from ANAM (the National Meteorological Agency of Burkina Faso). The objective of this study is the experimental analysis of a solar dryer with an unglazed parabolic trough collector. The work aims to evaluate its performance using new types of reflectors and absorbers, as well as to analyze the thermal performance of the collector and the dryer, and the drying kinetics of plantain and okra under real-world conditions. The studied products were washed and cut into homogeneous circular pieces and initially weighed, then distributed on the racks without overlapping. Irradiation and temperature data were recorded every five minutes. The measuring equipment included a data logger, a solarimeter, and an electronic balance. For 1000 g of banana, drying lasted 20 hours (over 2.5 days), with an average temperature of 50.9°C in the dryer. The final mass represented 32.8% of the initial mass. For 600 g of okra, drying took 8 hours, with an average temperature of 52.24°C. The final mass represented 9.66% of the initial mass. The average thermal efficiency of the collector was 68%. The overall efficiency of the dryer was evaluated at 20.24%. The average solar radiation recorded was 615 W/m². The drying kinetics for both products showed a decreasing phase, with a rapid reduction in moisture content at the beginning, followed by a gradual slowdown. The results are conclusive, highlighting that indirect solar dryers are a sustainable and cost-effective drying solution, offering better control over product quality.