ABSTRACT
High temperature drying of softwood is used because it provides much faster drying rate than is possible at lower temperatures. However, the occurrence of some drying defects limits its use where the quality is critical. In order to understand the drying phenomena and to describe the drying processes, numerous mathematical models have been developed in the past two decades.
The diffusion model is the earliest attempt to describe wood drying processes and is relatively simple in form, so it is often used for stress analysis. However, further substantial work is still required before it is possible to apply the stress model to kiln control.
Recently, transport-based mathematical models have been receiving attention in modelling studies. This review discusses one of these models, a physiologicaltransport-based model, which has been further applied to the drying of mixed sap/heartwood boards and the drying of a kiln-wide stack. The mixed boards with a thin heartwood layer parallel to the flat surface are considered to have added difficulty in drying. In the analysis of the timber stack drying, a kiln-wide model is proposed in which the above physiological-transport-based model is used to generate the characteristic drying curves. Airflow reversal is essential in kiln 180drying to reduce drying lag across the kiln stack. The kiln-wide model is used to investigate the effects of airflow reversal strategies as well as providing information to confirm the need to adjust the kiln drying schedule or determine the endpoint of drying.
