Thermodynamic Evaluation of the Forced Convective Hybrid-Solar Dryer during Drying Process of Rosemary (Rosmarinus officinalis L.) Leaves

Abstract

This study aimed to examine the energy and exergy indices of the rosemary drying process in a hybrid-solar dryer (HSD) and the effects of air-drying parameters on these thermodynamic indices. Drying experiments were carried out at four levels of air temperature (40, 50, 60, and 70 ∘C) and three levels of air velocity (1, 1.5, and 2 m/s). Energy and exergy were calculated by application of the first and second laws of thermodynamics. Based on the principal laws, energy efficiency, exergy losses, and exergetic improvement potential rate, were evaluated. The results showed that the energy utilization ratio (EUR) ranged from 0.246 to 0.502, and energy utilization (EU) ranged from 0.017 to 0.060 (kJ/s). Exergy loss and efficiency varied from 0.009 to 0.028 (kJ/s) and from 35.08% to 78.5%, respectively, and increased with increased temperature and air velocity. It was found that the exergy loss rate was affected by temperature and air velocity because the overall heat transfer coefficient was different under these conditions. By comparison, with increasing temperature and air velocity, the exergy efficiency increased. Because most energy is used to evaporate moisture, this behavior may be explained by improved energy utilization. The drying chamber sustainability index ranged from 0.0129 to 0.0293. This study provides insights into the optimization process of drying operations and operational parameters in solar hybrid dryers that reduce energy losses and consumption.

Modeling and Optimization of Energy and Exergy Parameters of a Hybrid-Solar Dryer for Basil Leaf Drying Using RSM

“…In other words, the water moved from points with higher moisture to points with lower moisture during the drying time, and the movement of water from the sample to the surface of the product was controlled by molecular diffusion. These results are consistent with the findings of the previous researchers, namely, Karami et al [33] for rosemary in a solar-convection dryer, Moussaoui et al [45] for apple in a hybrid solar-electrical forced convection dryer and Tagnamas et al [46] for carob seeds in a convective solar dryer.…”

“…In other words, the EU increased with an increasing air temperature and bed thickness; thus, the temperature of the air and the bed thickness were directly related to the EU. In this regard, the increase in energy utilization may be because the enthalpy supplied increased with the increasing drying air temperature and bed thickness, which in turn led to an increase in the energy utilization, since the EU is directly related to enthalpy [33]. Moreover, these results agreed well with Das et al [52] and Pattanayak et al [53].…”

“…The following equation was also used to determine the specific heat capacity of the dryer inlet and outlet air [33][34][35]:…”

“…Finally, Equations ( 10)-( 13) were utilized to calculate the rate of heat removed from the air leaving the dryer and the heat loss from the dryer body, as well as the energy utilization ratio (EUR) [31,33]:…”

“…In general, the exergy analysis was performed according to the first and second laws of thermodynamics, which was evaluated to obtain the specific exergy of air, exergy loss, and exergetic efficiency of the dryer chamber using Equations ( 14)-( 16) [33,34]:…”