Study on Moisture Movement in Wood with X-ray CT scanner.

用X射线CT扫描仪对干燥过程中水分分布进行无损检测。在本研究的第一阶段，研究了从CT扫描仪直接获得的总CT数中区分仅属于水分的CT数的方法，以及提高用硅橡胶袋包裹样品测量水分的准确度的方法。在干燥过程中，应用该方法对厚1/4锯材(厚度6 cm)在干燥过程中的水分分布进行了检测，测量了厚度方向上水分分布的变化。该样品可能具有水分运动的均质特性。同时，假定扩散系数随含水率的变化而连续变化。在此基础上，根据扩散系数与含水率的关系，反算出样品表面的含水率。用有限差分法求解Fick第二定律时，表面含水率在高含水率范围内应取6%左右的高值，在低含水率范围内应取高于平衡含水率的3~4%。以含水率为驱动力描述水分运动，扩散系数随含水率变化基本恒定。

Moisture distribution in drying were non-destructively detected with X-ray CT scanner. In the first stage of this research, methods were investigated to distinguish CT number attributed the moisture only from total CT number obtained directly with CT scanner and to improve the accuracy of moisture measurment using silicon rubber bags surrounding the sample. Moisture contents on internal cross section could be non-destructively measured in the finest of 1% below 40% range.In the second stage, applying the method to detect the moisture distribution of Douglas-fir thick quarter sawn lumber (6 cm thickness) in drying, change of moisture distribution in thickness direction was measured. The sample had probbably a homogeneous property for moisture movement. Also, it was assumed that the diffusion coefficient was continuously changing with moisture content. On this assumption, moisture contents on the surface of sample were reversely calculated from the relationship between diffusion coefficient and moisture content. Moisture content on the surface should be set the higher value of about 6% in high moisture content range and the higher value of 3-4% in low range than equilibrium moisture contents, in solving the Fick's 2nd law with the finite difference method. Describing moisture movement with moisture content as driving force, the diffusion coefficient was almost constant with moisture content change.