A theoretical, numerical and experimental study of heat and mass transfer in wood during drying

The United States is one of the world's major consumers of wood and wood products. For most applications, green wood must undergo a drying process before it is ready for use. Despite the fact that wood has a complicated structure, most previous drying models have assumed that wood is a homogeneous and isotropic material. This results in significant differences between the experimental data and the numerical predictions.; This dissertation systematically investigates, from the theoretical, numerical, and experimental aspects, the effects of the heterogeneous and anisotropic nature of wood on the heat and mass transfer process during drying. A theoretical model has been derived based on the fundamental equations for thermodynamics and heat, mass and momentum transport. This is the first model which accounts for the heterogeneous and anisotropic wood structure. The model is applicable to both diffusive and capillary moisture transport and to drying in any transverse direction. The model, which has been implemented in a finite difference program, is capable of predicting the heterogeneous and anisotropic effects on the moisture as well as temperature distributions in wood during drying.; In order to verify the model equations, a corresponding experiment has been designed and conducted. The measurement of local moisture content, both internally and at the surface, has been accomplished using a {dollar}gamma{dollar}-ray attenuation system and a near-infrared reflectance analyzer, respectively. In particular, the near-infrared reflectance measurements of the surface moisture are the first of their kind. A series of experimental tests have been conducted for drying in various transverse directions. By showing the significant non-uniform moisture distribution in the radial direction and non-uniform drying on the different sides of the sample, the test results indicate that the heterogeneity and the anisotropy of wood structure have significant impacts on heat and mass transfer in wood during drying. The experimental results also show that the moisture transport undergoes a transition period from capillary transport at moisture content above the fiber saturation point to diffusive transport at moisture content below the fiber saturation point. The model predictions are in good agreement with the experimental results.