Moisture transverse moving mechanism during presteamed oak lumber drying.

Effect of steaming at 100 °C, 80 °C and 60 °C dry-bulb temperature and 0 °C wet-bulb depression for 4 hours prior to drying on the drying rate and drying deformation of 25.4 mm thick oak lumbers during kiln drying was explored in this study. The results showed that presteaming delayed the drying time by at least 19 percent, and increased the crooks and bows of the lumbers. The mechanism that presteaming delayed the drying time is attributed to the smaller and fewer moisture transverse pathways inside the surface layers of presteamed lumbers. These pathways decrease the moving rates of the bound water and the water vapor from the inner part to the surface layers of presteamed lumbers during the middle and last stage of drying because of reduced distance between the microfibrils and increased crystallinity.