Simplifying convective heat and mass transfer in moisture desorption of beech wood by introducing characteristic transfer coefficients

Abstract

This paper presents the effect of forced convective heat and mass transfer coefficients on the predictive ability of a dynamic isothermal set of coupled partial differential equations. The analysis showed that this two coefficient one-dimensional model resulted in a very good prediction of the experimental data. The concept of experiment involves: six temperatures, six relative air humidities and three values of circulation velocity. Dimensions of beech (Fagus moesiaca) wood samples were 250 x 80 x 25 mm. The experimental installation, designed and constructed for this study, enables the drying process of relatively small samples to be similar to the drying process of real timber. The coefficients of internal conductivity of moisture and checking were calculated by a specially designed computer program for various regimes of drying. The cases with the extreme coefficients were analysed and the analytical dependence was obtained for the coefficient of internal moisture conductivity depending on temperature, instantaneous and initial moisture of wood, and the wood specimen being dried. Finally, an optimal drying process as well as a drying process producing the material of desired quality under the minimum drying costs is suggested.