The Application of Mathematical Models to the Commercial High-Temperature Drying of Softwood Lumber

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, numcrous 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. transpon-based mathematical models have been receiving attention in modelling studies. This review discusses one of these models, a physiological-transport-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 heanwood 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-transpon-based model is used to generate the characteristic drying curves. Airflow reversal is essential in kiln

Keywords and phrases::

• airflow reversal
• drying stress
• heartwood
• kiln-wide drying model
• mixed sap/heartwood
• sapwood
• single board drying model
• stack of boards