Design and optimization of an active and passive mode indirect solar dryer to improve energy efficiency and sustainability

Abstract This paper compares the behavior of active (forced convection) and passive (natural convection) indirect solar dryers when it comes to drying green chilies, in terms of thermal behavior, drying kinetics and retentiveness of products. Similar climatic conditions were done so as to compare the rate of moisture removal, thermal efficiency as well as specific moisture extraction rate (SMER). The active dryer reached a high temperature in the drying chamber of 65°C and decreased moisture content of 85% to 10% (wb) in 6 h under similar input measures as compared to the passive dryer, which took 12 h with similar input measures. The active dryer registered SMER and thermal efficiency values of 0.75 kg/kWh and 55%, respectively, compared to 0.45 kg/kWh and 35% of the passive dryer. The quality analysis revealed that the active dryer was much better in terms of color retention and flavor stability because of reduced exposure time and higher heat transfer. In a nutshell, the active system decreased active time by 40% and energy used per unit product, thus showing that it would be appropriate in decentralized agricultural processing with the use of solar energy.