A heterogeneous three-dimensional computational model for wood drying

An accurate and efficient heterogenous three-dimensional computational model is developed for simulating the drying of wood. The complex macroscopic drying equations comprise a coupled and highly nonlinear system of partial differential equations. Due to the heterogeneous nature of wood, the physical model parameters strongly depend upon the local pore structure of the medium, the wood density variation within growth rings and the local variations in primary and secondary system variables. In order to provide a realistic representation of this behaviour, previously determined parameters derived using sophisticated image analysis methods and homogenisation techniques are used. Results are presented for a first generation virtual board description, where the board material properties vary along the section according to the pith position that defines the radial and tangential directions. These variations are assumed fixed throughout the longitudinal direction. The development of an accurate and efficient computational model requires the consideration of a number of significant numerical issues, including the virtual board description, the mesh design, the discretisation process, accurate flux approximations, and finally the solution of a large, nonlinear system. Each of these issues will be explored in this paper for the case of low temperature drying of softwood.