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Investigation into solar drying of potato: effect of sample geometry on drying kinetics and CO2 emissions mitigation

Journal of Food Science and Technology volume 52, pages 1383–1393 (2015)Cite this article

Abstract

Drying experiments have been performed with potato cylinders and slices using a laboratory scale designed natural convection mixed-mode solar dryer. The drying data were fitted to eight different mathematical models to predict the drying kinetics, and the validity of these models were evaluated statistically through coefficient of determination (R2), root mean square error (RMSE) and reduced chi-square (χ 2). The present investigation showed that amongst all the mathematical models studied, the Modified Page model was in good agreement with the experimental drying data for both potato cylinders and slices. A mathematical framework has been proposed to estimate the performance of the food dryer in terms of net CO2 emissions mitigation potential along with unit cost of CO2 mitigation arising because of replacement of different fossil fuels by renewable solar energy. For each fossil fuel replaced, the gross annual amount of CO2 as well as net amount of annual CO2 emissions mitigation potential considering CO2 emissions embodied in the manufacture of mixed-mode solar dryer has been estimated. The CO2 mitigation potential and amount of fossil fuels saved while drying potato samples were found to be the maximum for coal followed by light diesel oil and natural gas. It was inferred from the present study that by the year 2020, 23 % of CO2 emissions can be mitigated by the use of mixed-mode solar dryer for drying of agricultural products.

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Abbreviations

a,b,c:

Coefficients in thin layer model

k, k0, k1, g, n:

Constants in the model

Aa :

Aperture area of solar dryer (m2)

Ca, :

Net annual cost of the solar dryer (Rs)

CEF:

Carbon emission factor of fuel

Cp :

Specific heat capacity of the product (J/kg K)

CRFd,T :

Capital recovery factor

CUF:

Capacity utilization factor of solar dryer

d:

Discount rate in fraction

Em :

CO2 emissions embodied in the solar dryer (kg/m2)

Ep :

Specific energy required for drying the product (kJ/kg dry matter)

FCO:

Fraction of carbon oxidized during combustion of fuel

fi :

Fraction of crop currently being dried by ith fuel

fpp :

Correction factor for the purchasing power of the user

fr :

Fraction of crop used in raw form

fsol :

Correction factor for solar radiation availability

GEc :

Potential of mitigating gross fossil CO2 emissions (kg)

MRexp,i :

Experimental moisture ratio (dimensionless)

MRpre,i :

Predicted moisture ratio (dimensionless)

M:

Moisture content, dry basis (kg water/kg dry matter)

M0 :

Initial moisture content

Me :

Equilibrium moisture content

m:

Annual operation and maintenance cost of solar dryer as a fraction of its capital cost

N:

Total no of observations

n:

Number of constants

NEc :

Net annual potential of CO2 emissions mitigation (kg)

pc :

Cost of the solar dryer per unit aperture area (Rs/m2)

Qdry :

Potential amount of a cash crop for solar drying (kg)

Qgross :

Gross annual crop production (kg)

R2 :

Coefficient of determination

RMSE:

Root mean square error

χ2 :

Reduced chi square

T:

Useful life time of the solar dryer (years)

Tp :

Temperature of product (K)

t:

Drying period

UCdry :

Unit cost of solar crop drying (Rs/kg)

UCmit :

Unit cost of fossil CO2 emissions mitigation (Rs/kg)

ηd :

Thermal efficiency of the solar dryer

ηi :

Efficiency of utilization of ith fuel in a conventional dryer

λ:

Latent heat of vaporization (kJ/kg)

o:

At the beginning of drying

f:

Final value of moisture content

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Acknowledgment

The author would like to thank Dr Subodh Kumar, Centre for Energy Studies, IIT Delhi for providing the solar dryer to carry out the experiments.

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  1. Department of Agricultural & Food Engineering, Indian Institute of Technology, Kharagpur, 721 302, West Bengal, India

    P. P. Tripathy

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

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  • DOI: https://doi.org/10.1007/s13197-013-1170-0

Keywords

  • Mixed-mode solar dryer
  • Drying kinetics
  • Thin layer drying models
  • CO2 emissions mitigation
  • Fossil fuels saved