Thermo-enviroeconomic assessment of a solar dryer of two various commodities

The energy, environmental, and health issues necessitate the development of renewable energy-based food processing, especially solar drying. However, the low efficiency and high production cost of such systems are still challenges and have been widely considered. Accordingly, this work aims to present a solar drying system for processing two various products: eggplant and grapes. In advance, three types of solar air heaters were tested and compared to select a proper one for the drying system: finned plate, evacuated tube, and modified evacuated tube solar air heaters. The findings indicated that the modified evacuated tube solar air heater had the highest thermal efficiency (67.92%), exergy efficiency (2.97%), and average temperature difference (27.48 °C). Then, this selected heater was employed in the proposed drying system. The considered parameters included dryer exit temperature, mass ratio, water removal rate, overall thermal efficiency, and cumulative drying exergy efficiency. Additionally, economic and environmental calculations were used to estimate the drying cost for each product, the payback period for each type, and CO2 reduction. As a result, the cost per kg of drying eggplant and grapes was 3.38 and 8.16 $/kg, saving 66.24 and 29.07%, respectively.