The Optimisation of Drying Schedules for Pinus radiata Sapwood Boards

摘要

Optimal drying schedules have been predicted for the drying of Pinus radiata sapwood from an initial moisture content of 140% over a drying time of twenty-four hours for 50mm-thick boards. Initially, a single pair of dry and wet-bulb temperatures (108℃, 60℃) over the full time period is estimated to keep the total tangential strain under 50% of the predicted limiting failure value. However, after twelve hours drying, more severe conditions may be used, with the final moisture content predicted to be reduced from 8.2% for a constant set of conditions throughout the schedule (108℃, 60℃) to 2.4% when the dry-bulb temperature is raised from 108℃ to 122℃ after twelve hours. It is also possible to use a linearly increasing dry-bulb temperature after twelve hours, rising from 108℃ to 155℃ at the end of drying with a predicted final moisture content of 0.2%. However, to reduce the moisture content to only 10%, there is little difference between the ramped and two-step schedules, both yielding a total drying time of eighteen hours. The two-step schedule would be the easier to adopt in practice.