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Impact of wood variability on the drying rate at different moisture content levels

Berberović, Adin, Milota, Michael R.
Forest products journal 2011 v.61 no.6 pp. 435-442
Tsuga heterophylla, drying, earlywood, heartwood, latewood, lumber, pith, prediction, temperature, water content, wood, wood drying, wood properties
The impacts on drying behavior of basic density, initial moisture content, percentage and position of heartwood, ring count, rings from the pith, growth ring angle, and earlywood and latewood coverage on board faces were investigated for western hemlock (Tsuga heterophylla) lumber. Mathematical relations for the effects of wood properties and board geometric features related to position within its parental log were developed to predict the drying rate at four moisture content levels for drying temperatures of 80°C and 115°C. These relations were used for simulating wood drying as well as for predicting drying times of individual boards, which were used as a criterion for sorting green boards prior to entering their properties in the drying simulation. Drying rate was affected by basic density, initial moisture content, percent heartwood, and growth ring angle at 80°C and only initial moisture content at 115°C. Presorting into two groups based on these wood properties reduced the standard deviation of the final moisture content distribution by 40 percent.