Mass diffusivity of different species of wood in convective drying

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.