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

Hamed Karami,Robert Rusinek,Iman Golpour,Marek Gancarz,Mohammad Kaveh,Esmail Khalife,Bohdan Dobrzański

doi:10.3390/en14185835

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.

Highlights

IntroductionThe use of herbal medicines for treating an extensive range of diseases and/or modifying nonpathogenic conditions is increasing globally [1]
Thermodynamic calculations showed that the specific energy consumption decreased with higher input temperatures and velocities in the drying chamber
The effective moisture diffusivity (Deff ) values of rosemary samples varied between 4.8 × 10−10 and 1.57 × 10−9 m2 /s at a temperature range of 40–70 ◦ C using Fick’s diffusion model, and the activation energy changed from 16.9 to 25.3 kJ/mol

Summary

Introduction

The use of herbal medicines for treating an extensive range of diseases and/or modifying nonpathogenic conditions is increasing globally [1]. Due to its antiinflammatory and antioxidant properties attributed to ursolic acids and carnosol/carnosic, rosemary has been used mainly in traditional medicine, cosmetics, and pharmaceutical industries [2]. Rosemary is applied as an oral medicine to alleviate muscle spasms, dysmenorrhea, and renal colic due to its medicinal properties. It has antioxidant, antiviral, antifungal, antibacterial, antitumor, antidepressant, analgesic, and anti-inflammatory properties [2]. The Mediterranean region plays an important role in providing a major proportion of the flavorings and spices for numerous uses in global food chains [3]

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