Energy and Exergy Analysis of Drying Process of Lemon Verbena Leaves in a Solar Dryer

Document Type : Research Article

Authors

• M. Moradi
• J. Ghasemi
• H. Azimi-Nejadian

Department of Biosystems Engineering, College of Agriculture, Shiraz University, Shiraz, Iran

https://doi.org/10.22067/jam.v11i2.85801

Abstract

Introduction
Some unit operations of food process engineering such as drying consumes a high amount of energy. Therefore, analysis of energy and exergy can be a suitable method to manage the energy consumption of the drying. Hence, in the present research, analysis of energy and exergy for the drying process of lemon verbena leaves was performed.
Materials and Methods
A cabinet solar dryer was employed to investigate the energy consumption of thin layer drying of lemon verbena leaves. The dryer had a galvanized solar plate collector which had a surface area of 0.75 m2 and to absorb the maximum solar energy, the collector painted with the black color. The collector was set at an angle of 45 degrees relative to the horizon and an electric blower was installed in the bottom of the collector to blow the ambient air through the solar collector and hence, hot air entered the drying chamber to dry the lemon verbena leaves. In order to record the air temperature and humidity in different locations of the dryer, an Arduino board with 8 smart sensors (AM2301, with temperature accuracy of 0.5°C and humidity accuracy of 3%) were used. To obtain the initial moisture content of the leaves, they inserted in an electrical oven for 16 hours at a temperature of 70°C. In order to measure the moisture content of the leaves during drying, they weighted at different times using a digital balance (A & D, Japan with accuracy of 0.001 g).
Energy consumption rate of the drying was calculated by Equation (1):
Where, Ein: energy consumption rate (kW), : mass flow rate of drying air (kg s^-1), cp: specific heat of drying air (kJ kg^-1 °C^-1), Δt: temperature difference between the ambient air and drying air (°C).
Also, the specific energy consumption of drying (SEC) was calculated by Equation (2):
Where; SEC: Specific energy consumption (MJ kg-1 of removed water) t: drying time (s), and M: mass of removed water from the drying material (kg).
Also, useful power can be calculated from Equation (3):
Where; Eout: useful power (kW), ms: Evaporation rate (kg s^-1), lg: latent heat of vaporization (kJ kg^-1 of water)
In order to calculate energy efficiency, Equation (4) was used:
 
Also inlet and outlet exergy were calculated by equations (5) and (6), respectively:
 Where; T1: Inlet air temperature into the drying chamber (°C), T2: Outlet air temperature from the drying chamber (°C), T0: Ambient air temperature (°C).
Also, Equations (7) and (8) were used to calculate exergy efficiency and loss, respectively:
Results and Discussion
The results of energy analysis showed specific energy consumption (SEC) increased with increasing of drying temperature and decreasing of air velocity. Accordingly, in the air velocity of 2 m s-1 and the temperatures of 30, 40, and 50 ˚C, SEC were 276.3, 694.7, and 708.0 MJ kg^-1 of removed water, respectively. While SEC for an air velocity of 2.5 m s^-1 and air temperatures of 30, 40, and 50 ˚C were 266.9, 469.8, and 638.0 MJ kg^-1 of removed water, respectively, the corresponded values for air velocity of 3 m s^-1 were as 217.0, 391.3, and 501.8 MJ kg^-1 of removed water, respectively. Also, the results revealed that with an increase of temperature and a reduction of velocity, energy efficiency reduced, so that the maximum value of energy efficiency observed in an experiment with temperature of 30˚C and velocity of 3 m s^-1. Also, the highest value of exergy efficiency obtained in temperature of 50˚C and velocity of 3 m s^-1.
Conclusion
A hot air solar dryer was used for drying lemon verbena leaves. Results of specific energy consumption of drying showed a high amount of fossil fuels can be saved by using this dryer. Also, from the aspect of energy and exergy efficiency, using of the dryer in the lower temperature and higher air velocity is recommended.

Keywords

• Carbon Dioxide
• Energy Efficiency
• Renewable energy resources
• Specific energy consumption

20.1001.1.22286829.1400.11.2.22.7

Open Access

©2020 The author(s). This article is licensed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source.

References

1. Akpinar, E. 2010. Drying of mint leaves in a solar dryer and under open sun: Modeling, performance analyses, Energy conversion and management 51: 2407-2418.

2. Bagheri, H., A. Arabhoseini, and M. H. Kianmehr. 2015. Energy and exergy analyses of thin layer drying of tomato in a forced Solar Dryer. Biosystems Engineering 46 (1): 39-45. (In Farsi).

3. Boulemtafes-Boukadoum, A., and A. Benzaoui. 2011. Energy and exergy analysis of solar drying process of Mint. Energy Procedia 6: 583-591.‏

4. Dinçer, İ., and C. Zamfirescu. 2015. Energy and Exergy Analyses of Drying Processes and Systems. In Drying Phenomena (eds İ. Dinçer and C. Zamfirescu). doi:10.1002/9781118534892.ch4

5. Duffie, J. A., and W. A. Beckman. 1991. Solar Engineering of Thermal Processes. 2nd ed., John Wiley and Sons, Inc., New York, USA. 919p.

6. Ferhat, M. A., B. Y. Meklati, J. Smadja, and F. Chemat. 2006. An improved microwave Clevenger apparatus for distillation of essential oils from orange peel. Journal of Chromatography A 1112: 121-126. doi:10.1111/jfpp.12930

7. Fudholi, A., K. Sopian, M. Y. Othman, and M. H. Ruslan. 2014. Energy and exergy analyses of solar drying system of red seaweed. Energy and Buildings 68: 121-129.‏

8. Habibi Asl, J., L. Behbahani, and A. Azizi. 2017. Evaluation and comparing of natural and forced solar dryer for mint drying in Khuzestan province.‏ Journal of Agricultural Machinery 7 (1): 114-125. (In Farsi).

9. Manikantan, M. R., P. Barnwal, and R. K. Goyal. 2014. Drying characteristics of paddy in an integrated dryer. Journal of Food Science and Technology 51 (4): 813-819. https://doi.org/10.1007/s13197-013-1250-1.

10. Momeni, T., and N. Shahrokhi. 1991. Essential oils and their therapeutic actions. Tehran, Iran: University of Tehran. (In Farsi).

11. Moradi, M., M. A. Fallahi, and A. Mousavi Khaneghah. 2020. Kinetics and mathematical modeling of thin layer drying of mint leaves by a hot water recirculating solar dryer. Journal of Food Process Engineering 43:e13181. https://doi.org/10.1111/jfpe.13181.

12. Nazghelichi T., M. H. Kianmehr, and M. Aghbashlo. 2010. Thermodynamic analysis of fluidized bed drying of carrot cubes. Energy 35 (12): 4679-4684.

13. Seidi damyeh, M., and M. Niakosari. 2017. Ohmic hydrodistillation, an accelerated energy-saver green process in the extraction of Pulicaria undulata essential oil Industrial Crops and Products 98:100-107.

14. Tarhan. S., I. Telci, M. T. Tuncay, and H. Polatci. 2010. Product quality and energy consumption when drying peppermint by rotary drum dryer, Industrial Crops and Products 32 (3): 420-427. https://doi.org/10.1016/j.indcrop.2010.06.003.

15. Tasic, J. R., M. Gojak., N. L. Cupric, and M. R. Bozovich. 2018. Active Solar Dryer for Biological Materials. FME Transactions 46: 537-543. doi: 10.5937/fmet1804537T.

16. Tripathy, P. P. 2015. Investigation into solar drying of potato: effect of sample geometry on drying kinetics and CO2 emissions mitigation. Journal of Food Science and Technology 52 (3): 1383-1393. https://doi.org/10.1007/s13197-013-1170-0.

17. Tyagi, H. A. K. Agarwal, P. R. Chakraborty, and S. Powar. 2018. Introduction to Applications of Solar Energy. In: Tyagi H., Agarwal A., Chakraborty P., Powar S. (eds) Applications of Solar Energy. Energy, Environment, and Sustainability. Springer, Singapore, https://doi.org/10.1007/978-981-10-7206-2_1.

18. Yogendrasasidhar, D., and Setty, Y. P. 2018. Drying kinetics, exergy and energy analyses of Kodo millet grains and Fenugreek seeds using wall heated fluidized bed dryer. Energy 151: 799-811.

19. Zomorodian, A., and M. Moradi. 2010. Mathematical modeling of forced convection thin layer solar drying for Cuminum cyminum. Journal of Agricultural Science and Technology12: 401-408.