Abstract
In present communication, a solar dryer having semi-transparent photovoltaic thermal (SPVT) roof has been used to dry bitter gourd. Experimentation has been done and results were validated with linear regression method through mathematical modelling as well as for non-linear Artificial Neural Network (ANN) modelling has been used. The experimental data namely, ambient air temperature, moisture evaporated, bitter gourd surface temperatures, solar intensity on different surfaces of dryer, room temperature and relative humidity have been recorded for the climatic condition of Varanasi, UP, India. The numerical value of convective heat transfer coefficients for bitter gourd found to be between 0.69–14.45 W/m2 K. The results for mass transfer (moisture evaporated) during drying of bitter gourd from theoretical model (linear regression method and ANN) and experiments showed good agreement. Further, net electrical energy, thermal energy and overall thermal energy were found to be 0.62, 3.77 and 5.41 kWh/m2/day respectively. The payback period at 10% interest rate and 4% inflation rate with ₹ 50 ($0.77) and ₹ 100 ($1.54) saving rate per kg were found to be 1.47 and 0.72 years respectively.
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Abbreviations
- A t :
-
Area of tray (m2)
- Cf :
-
Specific heat of air (J/kg K)
- d :
-
Effective diameter of fan exit (m)
- El :
-
Electrical energy (kWh)
- h c :
-
Convective mass transfer coefficient due to moisture evaporation in crop drying (W/m2K)
- I t :
-
Solar intensity on the wall of drying chamber (W/m2)
- I eff :
-
Total radiation in the greenhouse chamber (W)
- K v :
-
Thermal conductivity of humid air (W/mK)
- L c :
-
Characteristic length or characteristic dimension of the tray (m)
- \( {\dot{m}}_f \) :
-
Mass flow rate of air (kg/s)
- N :
-
Fan speed (RPM)
- N 1 :
-
Number of fan
- P (Tp):
-
Partial vapour pressure of moist air at crop surface temperature
- P (Te):
-
Partial vapour pressure of moist air above crop surface
- P fan :
-
Power of fan (W)
- t :
-
Time interval (s)
- T a :
-
Ambient temperature (0C)
- T o :
-
Cell temperature for optimum cell efficiency i.e. 250C
- T c :
-
Cell temperature (0C)
- T r :
-
Drying chamber temperature (0C)
- \( {\dot{Q}}_{th} \) :
-
Thermal energy (kWh)
- \( {\dot{Q}}_{th, ov} \) :
-
Overall thermal energy (kWh)
- V v :
-
Average velocity of humid air over the grape surface (m/s)
- V 1 :
-
Effective wind velocity inside the greenhouse chamber (m/s)
- α c :
-
Absorptivity of solar cell
- β 0 :
-
Temperature dependent efficiency factor
- β c :
-
Packing factor of module
- η 0 :
-
Standard efficiency at standard condition
- η c :
-
Solar cell efficiency
- η m :
-
Module efficiency
- η th :
-
Thermal efficiency
- η th,ov :
-
Overall thermal efficiency
- τg :
-
Transmittivity of module glass
- γ e :
-
Relative humidity of moist air above crop surface
- λ :
-
Latent heat of vaporization (J/kg)
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Appendices
Appendix I
Uncertainty Parameters | Calculation |
---|---|
Temperature (WT,total) (Arises from thermocouples, digital thermometer, connection point and reading errors) | WT,total = [(Wthermocouple)2 + (Wthermometer)2 + (Wconnection point)2 + (Wreadings)2]1/2 = [0.12 + 0.12 + 0.12 + 0.12]1/2 = 0.20 |
Mass measurement (Wm,total) (Digital balance and reading) | Wm,total = [(Wdigital balance)2 + (Wreadings)2]1/2 = [(1)2 + (1)2]1/2 = 1.4 |
Air velocity measurement (Wv,total) (Anemometer and reading) | Wv,total = [(Wanemometer)2 + (Wreadings)2]1/2 = [(0.1)2 + (0.1)2]1/2 = 0.14 |
Relative humidity measurement (Wrh,total) (Humidity-meter and reading) | Wrh,total = [(Whumidity meter)2 + (Wreadings)2]1/2 = [(0.1)2 + (0.1)2]1/2 = 0.14 |
solar intensity measurement (Ww,total) (Digital Solarimeter and reading) | Ww,total = [(Wdigital solarimeter)2 + (Wreadings)2]1/2 = [(1)2 + (1)2]1/2 = 1.4 |
Total uncertainty in experimental measurement (W ex,total ) | Wex,total = [(WT,total)2+ (Wm,total)2+ (Wv,total)2+ (Wrh,total)2+ (Ww,total)2]1/2 = [(0.2)2+ (1.4)2+ (0.14)2+ (0.14)2+ 1.4)2]1/2 = ± 2% |
Appendix II
Various design parameters taken for numerical computation.
αc = 0.9 | τg = 0.9 | βc = 0.75 |
---|---|---|
η0 = 0.15 | ρ = 1 kg/m3 | N = 1200 rpm |
Am = 5.75 m2 | At = 1.62 m2 | Af = 5.3 m2 |
Cf = 1005 J/kg K | d = 0.12 m | l = 0.9 m |
b = 0.9 m | t = 3600 s |
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Tiwari, S. ANN and mathematical modelling for moisture evaporation with thermal modelling of bitter gourd flakes drying in SPVT solar dryer. Heat Mass Transfer 56, 2831–2845 (2020). https://doi.org/10.1007/s00231-020-02886-x
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DOI: https://doi.org/10.1007/s00231-020-02886-x