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Mass diffusivity of different species of wood in convective drying

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Abstract

This study is devoted to the determination of the diffusion coefficient in convective drying of four local wood species: Aleppo pine, Stone pine, Zeen oak and date palm. A numerical method based on a diffusive model is used which consists of three complementary steps: experimentation, analysis of experimental data and minimization of the gap between experimental drying kinetics data and calculated ones. The coefficient of water for the four wood species is considered depending on both temperature and moisture content, and is obtained by the numerical solution of the conservation equation of the solid phase and the water transfer equation coupled to the shrinkage rate of the solid phase. The found values of diffusion coefficient are consistent with the range of variation in the literature. The mass diffusion coefficient varies with increase in temperature between 1.510−11 and 4.10−11 (m2/s) for the Aleppo pine, Stone pine and Zeen oak woods, however for the “palm wood”, it varies from 10 to 11 to 6.10−11 (m2/s). Arrhenius type relationship allows determining the activation energy, which varies between 135.64 and 150.49 (kJ/mol) for all species of wood treated, and these values are comparable with those of other species cited in literature.

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Abbreviations

aw :

Water activity (%)

C:

Concentration (kg m−3)

D:

Moisture diffusivity (m2/s)

D0 :

Arrhenius factor (m2/s)

db:

Dry solid

Ea :

Activation energy (kJ/mol)

HR:

Relative humidity (%)

Km:

Mass transfer coefficient (m s−1)

L:

Length of the sample (mm)

T:

Tangential of the sample (mm)

Mv :

Vapor molar mass (kg/mol)

m:

Mass (kg)

P:

Pressure (Pa)

Q:

Heat (J)

r:

Radial of the sample (mm)

R:

Ideal gas constant (J mol−1 k−1)

Re:

Reynolds number

Rv:

Volumetric shrinkage coefficient (%)

t:

Time (s)

T:

Temperature (°C, K)

Sc:

Schmidt number

u:

Speed (m s−1)

V:

Volume (m3)

X:

Moisture content (kg water/kg ds)

\(\mu ~\) :

Dynamic viscosity (kg m−1 s−1)

\(\beta\) :

Coefficient of shrinkage

\(\lambda\) :

Thermal conductivity (W m K−1)

\({{\uprho}}\) :

Density (kg m−3)

0:

Initial

a:

Air

l:

Liquid

s:

Solid

evap:

Evaporation

conv:

Convective

cal:

Calculated

eq:

Equilibrium

exp:

Experimental

surf:

Surface

FSP:

Fiber Saturation Point

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Acknowledgements

My sincere and heartfelt thanks to Professor Guizani AmenAllah, to the researcher Ben Makhlouf Naima and to the technician Zaaraoui Abdelrazek.

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Authors and Affiliations

  1. Laboratoire d’énergétique et des transferts thermique et massique, Faculté des sciences de Tunis, Université de Tunis El Manar, Campus Universitaire Manar II, 2092, Tunis, Tunisia

    S. Azzouz, K. Ben Dhib, R. Bahar, S. Ouertani & A. Elcafsi

  2. Laboratoire de Gestion et de Valorisation des Ressources Forestières, Institut National de Recherches en Génie Rural, Eaux et Forêts (INRGREF), Rue Hédi KARRAY BP 210, 2080, Ariana, Tunisia

    M. T. Elaieb

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  1. S. Azzouz
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  2. K. Ben Dhib
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  3. R. Bahar
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  4. S. Ouertani
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  5. M. T. Elaieb
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  6. A. Elcafsi
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Correspondence to S. Azzouz.

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Azzouz, S., Ben Dhib, K., Bahar, R. et al. Mass diffusivity of different species of wood in convective drying. Eur. J. Wood Prod. 76, 573–582 (2018). https://doi.org/10.1007/s00107-017-1212-9

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  • DOI: https://doi.org/10.1007/s00107-017-1212-9

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