Energy and exergy analysis of an indirect solar dryer based on a dynamic model

Sun is a clean and available sustainable energy source. The usage of sustainable energy in various industries such as agriculture is taking into consideration during the early years. One application is dehydration by using an indirect solar dryer, which was adopted in this study. A dynamic model was presented in which the calculation of the solar radiation received in the tiled surface of the collector, temperature variation along the collector, the kinetics of moisture reduction and temperature variation of the drying material were taken into consideration. The model was validated and confirmed with high accuracy by test results in three states of mass flow rates of air. The effects of air velocity, the glass cover thickness and the length of the collector took into consideration in the analysis as effective parameters. The thermal analysis was accomplished by using energy and exergy analysis. To energy analysis, the values of received and used energy were calculated in addition to energy utilization ratio and for exergy analysis, the irreversibility at collector was calculated as well as the exergy efficiency of drying in the chamber. Energy and exergy analysis revealed more stream exergy for higher speed air and hence, lower irreversibility. Besides, the defined exergy efficiency was independent of the material mass despite the exergy destruction or energy efficiency, which means a suitable criterion for the system analysis. The model was in good agreement with the experiments so that the deviation from the best fit line (y = x) in the model-experiments curves were 2.37% for radiation estimation, 4% for the outlet air temperature of the collector, 1% for the material temperature and 4.8% for the moisture ratio of the drying material. The model also revealed two critical moisture ratio of 0.75 and 0.23 in the drying process so that the maximum exergy destruction was observed at the first one and the maximum exergy efficiency was 22% for the dryer. (C) 2019 Elsevier Ltd. All rights reserved.