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Investigation on rough rice drying kinetics at various thin layers of a deep bed

Heat and Mass Transfer volume 50, pages 1717–1725 (2014)Cite this article

Abstract

Moisture content gradients along the bed column are commonly neglected during simulation of deep-bed grain drying. In this study, rough rice drying kinetics at various thin layers of a deep bed was investigated. The experiments were conducted under different drying conditions and the data were compared with the values predicted by a previously developed non-equilibrium model for numerical simulation of grain drying. The moisture content gradients related to the rough rice column indicated that the higher the drying layer, the more was the moisture content at each drying time. The constant drying rate period was observed neither for any thin layers nor for the entire drying column. The drying rate of the lower layers continuously decreased with drying time, whereas that of the upper layers firstly increased and then decreased. The implemented model predicted drying process with a high accuracy at various layers. However, the values of maximum relative error (RE max ) and mean relative error (MRE) increased as the air temperature increased, and reversely decreased with the air velocity. The higher values of MRE and RE max were related to the layer 1 (0–5 cm bed height) at temperature of 60 °C and air velocity of 0.4 m s−1, and the lower values belonged to the layer 4 (15–20 cm bed height) at temperature of 40 °C and air velocity of 0.9 m s−1.

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Abbreviations

Ca :

Specific heat capacity of dry air (J kg−1 K−1)

Cp :

Specific heat capacity of dry grain (J kg−1 K−1)

Cv :

Specific heat capacity of water vapor (J kg−1 K−1)

Cw :

Specific heat capacity of water, (J kg−1 K−1)

ha :

Grain bed volumetric heat transfer coefficient (J m−3 K−1 s−1)

hv :

Latent heat of vaporization (J kg−1)

M:

Moisture content of grain (kg kg−1, d.b)

Me :

Equilibrium moisture content of grain (kg kg−1, d.b)

MRE:

Mean relative error (%)

RE:

Relative error (%)

RH:

Relative humidity (%)

S:

Cross-sectional of the bed (m2)

t:

Time (min)

T0 :

Reference temperature (K)

Ta :

Air temperature (K)

x:

Bed coordinate (m)

X:

Drying constant

Y:

Drying constant

y′:

Absolute humidity of air (kg kg−1)

ρa :

Air density (kg m−3)

ρp :

Particle density of grain (kg m−3)

ν a :

Air velocity (m s−1)

ε:

Bed porosity (decimal)

λ0 :

Latent heat of vaporization at reference temperature (J kg−1)

θ:

Grain temperature (K)

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Acknowledgments

Financial support of this research was received from Isfahan University of Technology, which is gratefully acknowledged.

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Authors and Affiliations

  1. Department of Mechanical Engineering of Biosystems, Shahrekord University, Shahrekord, Iran

    Mehdi Torki-Harchegani

  2. Department of Agricultural Machinery Engineering, College of Agriculture, Isfahan University of Technology, 84156-83111, Isfahan, Iran

    Morteza Sadeghi

  3. Department of Chemical Engineering, Isfahan University of Technology, 84156-83111, Isfahan, Iran

    Ahmad Moheb & Zahra Naghavi

Authors
  1. Mehdi Torki-Harchegani
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  2. Morteza Sadeghi
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  3. Ahmad Moheb
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  4. Zahra Naghavi
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Correspondence to Mehdi Torki-Harchegani.

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Torki-Harchegani, M., Sadeghi, M., Moheb, A. et al. Investigation on rough rice drying kinetics at various thin layers of a deep bed. Heat Mass Transfer 50, 1717–1725 (2014). https://doi.org/10.1007/s00231-014-1378-1

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  • DOI: https://doi.org/10.1007/s00231-014-1378-1

Keywords

  • Control Volume
  • Maximum Relative Error
  • Mean Relative Error
  • Rough Rice
  • Enthalpy Balance