板材

An aim of this study is to find the law which governs the process of the drying of wood. In drying a board of wood, if its breadth and length are extremely large , compared with the thickness, we can safely assume that the evaporation of water take place only in the direction perpendicular to the two parallel surfaces of the largest area, and can neglect the evaporation from other directions. In this case, with analogous reasoning as in the case of Fourier's theory of heat conduction, we obtain the following differential equation, (snip)(1) : where θ is water content in the wood at the depth of x from the surface, expressed as a percentage of the absolute dry weight of the wood, t is times of drying, and h is a coefficient varying with the condition of wood. We obtained the following expression as a approximate solution of (1), (snip)(2) : under the next three boundary conditions, viz. (snip)(3)(4)(5) : where K is water content in equilibrium with the given temperature and humidity condition, and θ0 is initial moisture content (when t=0). Integrating (2) with regard to x between the limits of x=0 and x=1. and deviding by 1, the average water content ? in the wood of thickness of 1 is evaluated as follows, (snip)(6) : The theory was verified by the experiments. In those experiments, fourteen pieces of Sugi (Cryptomeria japonica, Don.) and Akamatu (Pinus densiflora, S. et Z.) were dried in the thermostat for over 150 hours at a temperature of 70℃. The results of the experiments agreed fairly with the theory as shown in the figures 1-4 and tables I?IV.