Abstract
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.
Highlights
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
25.4 mm thick oak lumbers were kiln dried after steamed at 100 °C 80 °C and 60 °C dry-bulb temperature and 0 °C wet-bulb depression for 4 hours in order to determine effect of presteaming on the drying rate and drying deformation of the lumbers
This tendency implies that the moisture transverse pathways in the surface layers of presteamed specimens become smaller and/or fewer compared to control specimens, and which increases as presteaming temperature increased
Summary
25.4 mm thick oak lumbers were kiln dried after steamed at 100 °C 80 °C and 60 °C dry-bulb temperature and 0 °C wet-bulb depression for 4 hours in order to determine effect of presteaming on the drying rate and drying deformation of the lumbers. The permeability during drying and the crystallinity after drying inside the. Surface layers of lumbers were measured in order to ascertain moisture transverse moving mechanism during drying in this study. Presteaming delayed the drying time by at least 19 percent because the fewer and smaller moisture transverse pathways inside the surface layers of presteamed lumbers decrease the moving rates of the bound water within the cell walls and the water vapor in the lumens from the inner part to the surface layers of presteamed lumbers during the middle and last stage of drying, owing to reduced distance between the microfibrils and increased crystallinity. Presteaming significantly increased the crooks and bows of the lumbers because of the larger compressive stresses after stresses reversed
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