Determining the Influence of Sample Thickness on the High-Temperature Drying of Beech Wood (Fagus sylvatica L.)

Abstract

Drying time reduction has always been a major concern in the drying process and is achievable by increasing the temperature of the surrounding air. To optimize the quality of the resulting material, drying conditions must be enhanced to reach a balanced correlation between the drying time and quality of the dried timber. This paper analyses the hightemperature drying of wood and the optimization of this process, as well as the effect that drying temperature and thickness of beech timber specimens has on the drying process. The high-temperature drying of beech wood was carried out by means of hot air in a laboratory drier for maximum 33 hours at maximum temperatures of 130 and 150 °C. The initial moisture content of samples was approximately 70%. The resulting drying times were short in comparison to conventional warm-air drying, which is caused by the high intensity of drying during the removal of bound water. Finally, it can be concluded that the thickness of the dried specimens is a significant factor in the process of high-temperature drying of beech wood INTRODUCTIONWood is the most frequently used material for interior and exterior structures because of its natural and aesthetic aspects and its simple processing. The drying of timber at temperatures above the boiling point of water is called high-temperature drying (Hillis 1984;Aydin and Colakoglu 2005). This technique has attracted considerable attention in recent years. The high-temperature drying of wood is an environmentally friendly method that is three to five times faster than warm-air drying (Trebula and Klement 2002). Drying wood at high temperatures (130 to 150 °C) is an effective method to improve the dimensional stability and biological durability of wood (Perré and Degiovanni 1990, 1999).Based on the cited work, it is reasonable to expect that in the high temperature drying of beech the loss of moisture will be directly proportional to the drying time. When the temperature is raised above 100 °C, the drying time will be shortened, with a faster decrease of moisture content. According to Poncsák et al. (2006), the influence of temperature is more pronounced at higher moisture content. Drying times are short in comparison to conventional warm-air drying, which is attributable to the high intensity of drying during the removal of bound water (Klement and Marko 2009). Kollman (1952) reported that high-temperature drying requires 25 to 60% less energy than does normal kiln-drying. This reduction in energy is attributed primarily to better heat transfer to the PEER-REVIEWED ARTICLE bioresources.com Klement & Huráková (2016). "Beech high-T drying," BioResources 11(2), 5424-5434. 5425wood and less heat loss through the kiln walls because drying time is shortened. The high temperature has a significant influence not only on the discoloration, but also on dimensional stability and mechanical properties of wood. However, the strength and especially toughness therewith is inevitable reduced (Okuyama et al. 1990). Burmester (1975) concludes that high-tempe...

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