Skip to main content

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


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.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8


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)


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

Me :

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


Mean relative error (%)


Relative error (%)


Relative humidity (%)


Cross-sectional of the bed (m2)


Time (min)

T0 :

Reference temperature (K)

Ta :

Air temperature (K)


Bed coordinate (m)


Drying constant


Drying constant


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)


Bed porosity (decimal)

λ0 :

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


Grain temperature (K)


  1. Brooker DB, Bakker-Arkema FW, Hall CW (1992) Drying and storage of grain and oilseeds. Van Nostrand Reinhold, New York

    Google Scholar 

  2. Zare D, Chen G (2009) Evaluation of a simulation model in predicting the drying parameters for deep-bed paddy drying. Comput Electron Agr 68:78–87

    Article  Google Scholar 

  3. Miranda M, Vega-Gálvez A, García P, Scala KD, Shi J, Xue S, Uribe E (2010) Effect of temperature on structural properties of Aloea vera (Aloe barbadensis Miller) gel and Weibull distribution for modelling drying process. Food Bioprod Process 88:138–144

    Article  Google Scholar 

  4. Singh NJ, Pandey RK (2012) Convective air drying characteristics of sweet potato cube (Ipomoea batatas L.). Food Bioprod Process 90:317–322

    Article  Google Scholar 

  5. Cenkowski S, Jayas DS, Pabis S (1993) Deep-bed grain drying. A review of particular theories. Dry Technol 11:1553–1581

    Article  Google Scholar 

  6. Barre HJ, Baughman GR, Hamdy MY (1971) Application of the logarithmic model to cross-flow deep-bed grain drying. Trans ASABE 14:1061–1064

    Article  Google Scholar 

  7. Bakker-Arkema FW, Bickert WG, Patterson RJ (1967) Simultaneous heat and mass transfer during cooling of a deep bed of biological products under varying inlet air conditions. J Agr Eng Res 12:297–307

    Article  Google Scholar 

  8. Spencer HB (1969) A mathematical simulation of grain drying. J Agr Eng Res 14:226–235

    Article  Google Scholar 

  9. Palancz B (1985) Modelling and simulation of heat and mass transfer in a packed bed of solid particles having high diffusion resistance. Comput Chem Eng 9:567–581

    Article  Google Scholar 

  10. Rumsey TR, Rovedo CO (2001) Two-dimensional simulation model for dynamic cross-flow rice drying. Chem Eng Process 40:355–362

    Article  Google Scholar 

  11. Izadifar M, Mowla D (2003) Simulation of a cross-flow continuous fluidized bed dryer for paddy rice. J Food Eng 58:325–329

    Article  Google Scholar 

  12. Wu B, Yang W, Jia C (2004) A three-dimensional numerical simulation of transient heat and mass transfer inside a single rice kernel during the drying process. Biosyst Eng 87:191–200

    Article  Google Scholar 

  13. Zare D, Minaei S, Mohamad Zade M, Khoshtaghaza MH (2006) Computer simulation of rough rice drying in a batch dryer. Energy Convers Manag 47:3241–3254

    Article  Google Scholar 

  14. Mohsenin NN (1986) Physical properties of plant and animal materials, 2nd edn. Gordon and Breach, New York

    Google Scholar 

  15. Stroshine R, Hamann D (1998) Physical properties of agricultural materials and food products. Department of Agricultural and Biological Engineering, Purdue University, West Lafagette

    Google Scholar 

  16. Amin MN, Hossain MA, Roy KC (2004) Effects of moisture content on some physical properties of lentil seeds. J Food Eng 65:83–87

    Article  Google Scholar 

  17. Naghavi Z, Moheb A, Ziaei-rad S (2010) Numerical simulation of rough rice drying in a deep-bed dryer using non-equilibrium model. Energy Convers Manag 51:258–264

    Article  Google Scholar 

  18. Vijayaraj R, Saravanan R, Renganarayanan S (2006) Studies on thin layer drying of bagasse. Int J Energy Res 31:422–437

    Article  Google Scholar 

  19. Fortes M, Okos MR (1981) Non-equilibrium thermodynamics approach to heat and mass transfer in corn kernels. Trans ASABE 22:761–769

    Article  Google Scholar 

  20. Henderson SM (1974) Progress in developing the thin layer drying equation. Trans ASABE 17:1167–1172

    Article  Google Scholar 

  21. Whitaker T, Barre HJ, Hamdy MY (1969) Theoretical and experimental studies of diffusion in spherical bodies with a variable diffusion coefficients. Trans ASAE 11:668–672

    Article  Google Scholar 

  22. Keey RB (1972) Drying principles and practice. Pergoman Press, New York

    Google Scholar 

  23. Fontana C (1983) Concurrent flow versus conventional drying of rice. Ph.D. Thesis, Michigan State University, East Lansing (MI)

  24. Wang CY, Singh RP (1978) A single-layer drying equation for rough rice. ASAE, St. Joseph

    Google Scholar 

  25. ASAE (2001) Guide for moisture measurement-ungrounded grain and seeds. ASAE Standard

  26. Lopez A, Pique MT, Romero A (1998) Simulation on deep bed drying of hazelnuts. Dry Technol 16:651–665

    Article  Google Scholar 

  27. Dincer I, Dost S (1995) An analytical model for moisture diffusion in solid objects during drying. Dry Technol 13:425–435

    Article  Google Scholar 

  28. Sitompul JP, Istadi I, Widiasa IN (2001) Modelling and simulation of deep-bed grain drying. Dry Technol 19:269–280

    Article  Google Scholar 

  29. Tang Z, Cenkowski S, Muir WE (2004) Modelling the superheated-steam drying of a fixed bed of brewers’ spent grain. Biosyst Eng 87:67–77

    Article  Google Scholar 

  30. Kalbasi M (2003) Heat and moisture transfer model for onion drying. Dry Technol 21:1575–1584

    Article  Google Scholar 

  31. Madhiyanon T, Soponronnarit S, Tia W (2001) A two-region mathematical model for batch drying of grains in a two-dimensional spouted bed. Dry Technol 19:1045–1064

    Article  Google Scholar 

  32. Dimitriadis NA, Akritidis CB (2004) A model to simulate chopped alfalfa drying in a fixed deep bed. Dry Technol 22:479–490

    Article  Google Scholar 

  33. Park KJ, Vohnikova Z, Brod FP (2002) Evaluation of drying parameters and desorption isotherms of garden mint leaves (Mentha crispa L.). J Food Eng 51:193–199

    Article  Google Scholar 

Download references


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

Author information

Authors and Affiliations


Corresponding author

Correspondence to Mehdi Torki-Harchegani.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


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