Study On Drying Characteristics Of China Fir Wood Bunch

Wood bunch drying is a vital stage in the manufacturing process of wood products from wood bunch such as parallel strand board because it directly determines production efficiency, energy consumption and quality. It is of special significance to study the drying characteristics newly developed products from fast growing wood in China today when the supply of wood product does not meet its demand.This study examines the drying characteristics of China fir wood bunch in high temperature and the functions of various factors on its drying efficiency and energy consumption. A special examination was made in the nature of moisture movement and heat transfer in the inner part of wood bunch, which results in the construction and solution of a mathematic model of their process. It contributes as a theoretical basis to the calculation of the technical parameter of and designing of solution to wood bunch drying. Major findings of this study go as the following:(1) A technique of arraying cutting as well as its device was invented, which enables the production of wood bunches with the set specification. It meets the technical demands of the production of wood-based panels and is a technical innovation of the processing of fast growing small diameter wood.(2) As the first ever practice of study method, this study explored the major drying characteristics of China fir wood bunch through large-scale experiment, which shows that, a. the technique of fast drying in high temperature applies to the process of wood bunch drying because it demands longer drying duration during the rise of temperature; b. the moisture movement in the inner part goes vertically as well as horizontally in the case of shorter wood bunch drying, both at similar speed; whereas it goes more horizontally than vertically in the case of longer wood bunch; c. the average drying rate tends to be larger when the initial moisture content is higher.(3) Also as the first ever practice of research method, the study mensurated the distribution of temperature and moisture content profiles in sealed wood of Chinese Fir whose opposite faces are subjected to constant but different temperature for a short time, the ratio of moisture content gradient to temperature (dM/dT). The results show that, the effect of heat proliferation was produced even in the function of short-term temperature gradient; at the same time, an moisture gradient was formed in he inner part of wood which was opposite to the temperature, and the ratio of dM/dT went below 0.9%/°C. The ratio of dM/dT tended to get larger and the heatproliferation tended to be more active when the wood temperature and its initial moisture content increased. Thus, wood temperature and its initial moisture content are fundamental factors in the effect of heat proliferation.(4) The driving force of free moisture and absorb moisture in wood interior under high temperature and their movement features were studied, which show that, a. the free moisture movement in high temperature drying acted as mass movement under capillary pressure or steam movement under pressure gradient. An equation of free moisture movement in high temperature drying was created accordingly, b. the diffused transfer of absorb moisture in high temperature drying acted as one under concentration gradient or steam diffused transfer under steam pressure gradient. An equation of absorb moisture movement in high temperature drying was also created, c. A general moisture diffusion coefficient was obtained through experiment, which indicates that the coefficient grows as the wood bunch diameter or its temperature increases.(5) The first ever mathematic model of heat and mass transfer in wood bunch drying under high temperature was created. Experiments showed that the equation is mostly workable in predicting average moisture content and temperature of China fir wood bunch in the process of high temperature drying. Hence, it contributes as a theoretical basis to wood bunch drying.(6) As an innovational research, this study also looked into the functions of fac...