engleski

Impact of various conventional drying conditions on drying rate and on moisture content gradient during early stage of beechwood drying

An appropriate moisture transport and a control of moisture distribution are needed from the early beginning of drying process, especially at drying of high dense and less permeable hardwoods. For determination of suitable process conditions at drying of European beechwood (Fagus sylvatica L.) the unidirectional drying kinetics, with an emphasis of free water removal was researched. We used radially oriented sapwood specimens, having thickness from 6 mm to 24 mm (ΔL = 6 mm). Series of conventional drying processes were carried out in the laboratory tunnel drier at constant climate (T = 30 °C) RH = 85%) and with varying air velocity (v) from 0.6 m/s to 7.6 m/s. During the drying, moisture content (MC), MC gradient and moisture flow were gravimetrically determined at successive time intervals. Drying rate generally increased with rising of air velocity and decreased with increasing thickness of wood. Relatively constant drying rate was present at the initial stage of drying of thin specimens (≤ 12 mm) in a short time interval, when low air velocity was used (≤ 2.5 m/s). Increasing of the air velocity (> 2.5 m/s) lead to early irreversible reduction of initial moisture flow and transition to the period of significantly falling drying rate, where the internal mass resistance predominated and caused high initial moisture content gradient. The diffusion barrier was induced at too fast free water removal which controlled further drying rate and significantly prolonged the drying process in continuation.

conventional kiln drying; drying rate; beechwood

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