| Summary: | 碩士 === 國立臺北科技大學 === 冷凍與低溫科技研究所 === 92 === This paper studied drying and dehydration of timber. The four drying methods included heat drying, vacuum drying, microwave heating drying, and vacuum microwave heating drying. The drying speed, the stress and strain of the timber after drying were compared. The experiments found that heat drying required the longest drying time; using the method to dry to 12% water content required 8-10 hours. The drying time required for microwave heating drying was 72 times shorter than heat drying; using the method to dry to 12% water content required 7-12 minutes. The drying time required for vacuum microwave heating drying was shorter than microwave drying; using the method to dry to 12% water content required 5-9 minutes. The reason was that in a vacuum environment, the water molecules inside the timber had outward movement trend. Thus, the drying speed of microwave heating was 1.2 times faster in atmospheric environment. Of those four methods, vacuum drying required the longest time. After 30 minutes of drying, the water content was 83%. The result was unsatisfactory. In stress tests, when the water content was 12% under heat drying method, the stress bearable to the timber was better than that of microwave and vacuum microwave heating methods. The reason was that when the timber was heated microwave, the temperature rise started from the inside. When the water content of the inside of the timber reduced to a specific level, ignition may occur and led to damage to the internal structure, and the bearable stress would reduce significantly. Therefore, attention should be paid to the power of microwave and the heating time length when using microwave heating method.
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