Performance evaluation of greenhouse solar dryer: Energy-exergy analysis, CFD simulation and eco-environmental assessment

Solar greenhouse drying is considered a useful solar dryer technology for tropical and subtropical countries. This study examined a Quonset Solar Greenhouse Dryer (QSGD) with a parabolic roof and polycarbonate sheets on a 2.47 x 6.0 m2 concrete floor, ventilated by two 220-V AC fans. The drying kinetics of mint leaves, energy-exergy analysis, Computational Fluid Dynamics (CFD) validation, economic viability and environmental impact were investigated. Mint leaves were dried from 85 % to 10 % moisture content in 3.5 h. The QSGD's energy and exergy efficiencies were 32 % and 22 %, respectively. The Discrete Ordinates (DO) radiation model simulated the effect of solar radiation inside the greenhouse dryer and the K-e model was used to account for the turbulent airflow. CFD 3-D simulations using ANSYS FLUENT ver.21 showed uniform temperature and airflow distribution, with good agreement between experimental and theoretical results. The outlet temperature ranged from 30 to 48 degrees C (experimental) and 34-50 degrees C (simulation) and also, higher air velocities were noted at the inlet and outlet. Environmental assessment revealed embodied energy of 47224.8 kWh, CO2 emissions of 9.7 tons and net CO2 mitigation of 130.7 tons over its lifetime. The Energy Payback Time (EPBT) and Payback Period (PBP) were 3.1 and 1.64 years, respectively.