Experimental Evidence and Computational Simulation of Heat Transfer in Greenhouse Solar Drying of Mesquite Pods

A greenhouse solar dryer was used to study the drying behavior of mesquite pods, and a radiation model for participating media was numerically solved to predict the air temperature in the dryer. The model was solved for a stationary state by considering the environmental conditions. The transfer coefficients were calculated for natural and forced convection. In the case of forced convection, an average airflow of 0.5668 m/s (SD = 0.1121) was provided over the trays. The weight of the pods, their temperature, air temperature, ambient temperature, relative humidity, and solar irradiation were recorded. The average heat transfer coefficients for natural and forced convection were 2.9294 W/m2 °C and 6.3772 W/m2 °C, respectively. The average mass transfer coefficients for natural and forced convection were 0.002987 kg/m2 s and 0.00601 kg/m2 s, respectively. The greenhouse dryer showed a high dependence on the weather conditions, showing important disturbances to air temperature. For the experiment with forced convection, a reabsorption of moisture was observed during the night; nevertheless, the final moisture content of the pods was below 0.05 g moisture/g dry matter, which was convenient for the subsequent grinding process. The radiation model correctly describes the average air temperature in the greenhouse volume. A reduction in thermal fluctuations will be important to improve the process.