A heterogeneous wood drying computational model that accounts for material property variation across growth rings

Abstract

In this work, a comprehensive two-dimensional drying model, known as TransPore, is extended so that the effect of material heterogeneity and local material directions on the heat and mass transport processes evolving within the medium can be investigated. The underlying mathematical theory enables the property variations as well as the spatial changes of local material directions to be taken into consideration throughout the computation. The model, which enables the behaviour of the moisture content, internal temperature and pressure fields to be monitored during the drying process, uses a control-volume finite-element (CV-FE) formulation, together with a suite of sophisticated numerical techniques to ensure both accurate and efficient simulation results. A board section of softwood is used to depict the possibilities offered by this model. In this case, the material directions vary along the section according to the pith position that defines the radial and tangential directions. In addition, the material properties change significantly from earlywood to latewood. A comparison of the overall drying kinetics generated by both the heterogeneous and the classical homogeneous models will provide a clear understanding of the impact and importance of treating the local wood properties when drying softwood.