Comparing Continuous and Cyclic Drying Schedules for Processing Hardwood Timber: The Importance of Mechanosorptive Strain

Abstract

This work compares a conventional continuous drying schedule with a solar cyclic drying schedule for the seasoning of an Australian hardwood timber, Eucalyptus grandis, focusing on the simulated stresses and strains developed during drying as a measure of timber quality. The cyclic drying schedule has been found to give lower instantaneous strains, due to the effect of mechanosorptive strains in relieving stresses both in the initial stages of drying and over the entire drying period. The gentler initial drying conditions during cyclic drying are also beneficial compared to the harsher and unmodulated nature of conventional drying schedules. Without the modulation of the external drying conditions in intermittent or cyclic drying, the mechanosorptive strains are unable to relax or mitigate the stresses that are caused naturally by timber drying. There is some support for these conclusions by comparison with industrial experience and previous laboratory practice for intermittent and cyclic drying.

Keywords:

• Drying-induced stress
• Stress–strain
• Wood drying

ACKNOWLEDGMENTS

This work has been supported by the Australian Research Council through the Linkage Grants Program and by Solarkilns Pty Ltd (Australia), particularly Greg Weir, whose financial support and patience have been greatly appreciated throughout the work.

Notes

Data from Waterson.^{[ 28 ]} MC = moisture content, DB = dry-bulb temperature, WBD = wet-bulb depression.