板材の乾燥について : 内部温度の上昇経過と水分々布

その他

Under the constant drying condition (dry bulb temp. 60℃, Wet-bulb temp. 35℃, relative humidity 20%) we made experiments on the drying of board (especially the elevating process of temperatures in both the surface and inner part of it and the moisture distribution in board during drying). Test pieces used here are flatsawn-disk (diameter : 5.0cm, thickness : 1.0cm) of Hinoki- (Chamaecyparis obtusa S. et Z.) and Hiba-wood (Thujopsis dolablata S. et Z). They were coated with urea-formaldehyde resin to prevent the drying from the sides of them and then soaked in water until saturated (initial moisture content : Hinoki-wood 201-204-208%. Hiba-wood 210-215-223%).
Results obtained are as follows;
1) The drying process (moisture content u : drying time Z), relationships between log. u and Z, and between evaporating velocity (w) and moisture content u are shown in Fig. 1. Fig. 2 and Fig. 3 respectively. From these figures we can obviously recognize two stage of drying i. e. first and second stage of falling rate of drying.
2) As the result of Fig. 2, the drying velocity (du/dz) of board in falling rate of drying was given by the following formula;
du/dz = -k (u-u_eq)
Coefficients k of Hinoki-and Hiba-wood are 0.144 and 0.223 respectively.
3) Moisture diffusivity K (in the diffusion equation eu/ez = K(e^2u)/(ex^2)) 注） of Hinoki-and Hiba-wood are 0.01314 and 0.02346, and diffusion coefficients
(λ = ((r_0)/(100))(((e/(ez))(∫udx))/((du)/(dx)))) 注）are 0.414×10^<-4> and 0.907×10^<-4> respectively (Table 1 and Table 2)
4) The moisture distribution in board during drying seems to be indicated by
sine-curve [u = u_eq + 4/π(u_0-u_eq)・e^<-(π/a)^2 k・z>・sin((πx)/a)].
5) The elevating process of the temperatures in the surface and inner part of board and moisture distribution in board during drying are shown in Fig. 5 and Fig. 6. We can recognize three periods concerning elevating process of temperature (i. e. heating period at first stage of drying, second stage of heating period and heating period at late stage of drying)
6) Relationship between evaporating velocity and temperature-elevating are shown in Fig. 7 and Fig. 8.
注）：この式の e は　天地逆。