Abstract
This paper describes the design considerations, followed by the results achieved during its testing and finally a comparison between those experimental results and a computational simulation. The design of the solar dryer was developed with the use of CAD drawing software. The wood-structured unit consists of a front-pass collector, glazed with a 0.6 mm polycarbonate sheet and a copper absorber plate of 0.85 m2 area, and a drying chamber, which holds four wooden aluminium-meshed trays for the drying of different products. The unit was tested under artificial and natural conditions. For the former, an artificial lighting equipment was used to simulate 760 W/m2 solar irradiation and for the latter the unit was tested under direct sun exposure. The temperature achieved on the absorber plate was 67 °C, while the air temperature reached during the indoor test at inlet, tray 1, tray 2, tray 3, tray 4 and outlet was 26, 44, 42, 40.5, 39 and 37 °C, respectively. The results show that it took 14 hours to reduce the moisture content of 2,69 kg of sliced bananas from 78% to 16.9, 17.8 17.7 and 21.2% on trays 1, 2, 3 and 4, respectively and to 20.2% with open sun drying. The thermal efficiency of the designed solar dryer was 37% and the dryer efficiency 14%. The results achieved during the indoor test were compared with a test under natural conditions and a computational simulation (CFD). In both cases similar tendencies were found, showing that the manufacturing was successfully achieved.
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Abbreviations
- A c :
-
Collector area, m2
- C p :
-
Specific heat at constant pressure, kJ/kg °K
- d :
-
Mass of the dry matter in the sample, kg
- g :
-
Acceleration due to gravity, 9.81 m/s2
- h :
-
Height of hot air column, m
- I :
-
Insolation incident on the absorber’s surface, W/m2
- I T :
-
Total solar radiation incident on the top surface,
W/m2
- L :
-
Latent heat of vaporization of water, kJ/kgH2O
- m :
-
Mass, kg
- m a :
-
Mass of drying air, kg
- \( {\dot{m}}_a \) :
-
Mass of air leaving the dryer per unit time, kg/s
- m i :
-
Initial mass of the product to be dried, kg
- M i :
-
Initial moisture content wet basis, %
- M f :
-
Final moisture content wet basis, %
- m v :
-
Mass of water removed from product, kg
- MC:
-
Moisture content
- OS:
-
Open sun
- P :
-
Pressure, Pa
- Q u :
-
Useful energy gained by collector, W
- Q useful :
-
Useful energy gained by collector, W
- Q Cond :
-
Conduction heat losses from the absorber, W
- Q Conv :
-
Convective heat losses from the absorber, W
- Q L :
-
Heat losses of the absorber, W
- Q g :
-
Heat gained by the air, W
- Q Rad :
-
Radiation heat losses from the absorber, W
- Q Ref :
-
Reflection losses from the absorber, W
- R :
-
Universal gas constant, 8.3 kJ/k mole K
- T :
-
Temperature, K
- T a :
-
Ambient air temperature, K
- T c :
-
Temperature of the collector’s absorber, K
- T i :
-
Initial temperature of drying air, K
- T f :
-
Final temperature of drying air, K
- U L :
-
Overall heat transfer coefficient of the absorber, W/m2K
- V :
-
Volume, m3
- w :
-
Mass of the wet product, kg
- α :
-
Solar absorptance of the absorber
- ρ 1 :
-
Density of air outside the dryer respectively, kg/m3
- ρ 2 :
-
Density of air inside the dryer, kg/m3
- η C :
-
Efficiency of the collector, %
- η d :
-
Drying efficiency, %
- \( \mathcal{R} \) :
-
Reflection coefficient of the absorber
- τ :
-
Transmittance of the glazing cover, W/m2
- τ d :
-
Drying time, s
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Mirzaii, H., Barbieri, J.P.N. (2020). Feasibility Study into Design, Development and Testing of an Indirect Multi-Rack Solar Dryer for Agricultural Products. In: Sayigh, A. (eds) Renewable Energy and Sustainable Buildings. Innovative Renewable Energy. Springer, Cham. https://doi.org/10.1007/978-3-030-18488-9_32
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DOI: https://doi.org/10.1007/978-3-030-18488-9_32
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