Stack-Wide Behavior for Hardwood Drying

The assessment and development of drying schedules for hardwood timber that account for stack-wide behavior is required for practical implementation in kilns of finite width. The concept of a characteristic drying curve was not found to be applicable for the hardwood timber considered here (Australian ironbark), so a full (Fickian) diffusion model was used. Air flow reversals every 4 h gave less variation in the average moisture contents across the stack than greater time periods between each reversal. An incorrectly timed air flow reversal was found to do more damage than no air flow reversals at all. Even with optimization of the drying schedules to account for stack widths, a reconditioning period is still needed to reduce the moisture content variation within the limits for a quality class of A (as defined by the Australian standards). The frequency of air flow reversals is recommended to be no greater than 4 h between each reversal in order to reduce the moisture content variation across the kiln within specified limits and limit the maximum strain to 1.8%.