【作者】 李延军；

【导师】 张璧光； 张齐生；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2005， 博士

【摘要】 木束的干燥是积成材人造板及其它以木束为原料的各种产品生产中的一个重要环节,它关系到生产的效益、能耗和产品质量。在目前我国木材供需矛盾日益突出的今天,研究速生材新产品原料木束的干燥特性,对提高木束干燥效益,降低成本具有重要意义。 本文较系统全面地研究了杉木木束在高温干燥过程中的干燥特性,分析了各因素对干燥效益和能耗的影响,尤其是研究了木束内部水分迁移和热量传导过程的规律,建立并求解了传热传质的数学模型,为确定木束干燥生产的工艺参数及控制方案提供了理论依据。本研究主要成果与创新点如下: 1、研制了适于杉木小径材的梳解设备与梳解工艺,使杉木小径材梳解后可获得特定规格尺寸且尺寸分布具有规律性的单根状木束条,能满足人造板生产工艺要求,是速生小径材高效加工利用的新工艺、新技术。 2、首次通过大量的试验和理论分析,较系统深入地研究了杉木木束高温干燥的基本特性。研究表明:①在木束的高温干燥中,升温阶段占据的干燥时间较长。木束的干燥宜采用高温快速干燥。②在短木束试件高温干燥时,其内部的水分的移动是在纵向和圆周方向同时进行的,并且移动的速度大致相当;而细长木束试件水分移动主要是以圆周方向为主的,随着试件的长度增加,圆周方向的水分移动对干燥速度的贡献率将逐渐占主导地位。③木束初含水率越高,则平均干燥速率越大。 3、首次通过试验测定了封闭杉木木材试件在短期温度梯度作用下,木材内部温度场和含水率场的分布,含水率梯度与温度梯度比值(dM/dT)的大小及其影响因素。研究表明:木材即使在短期温度梯度的作用下也会出现热扩散效应,在木材内部形成与温度梯度相反的含水率梯度场,dM/dT的比值在0.9%/℃以下;随着木材温度和初含水率的增加,木材中的dM/dT越大,热扩散效应越明显;随着作用时间的延长,木材中的dM/dT增加。其中温度和含水率是影响热扩散效应的最主要因素。 4、分析了高温干燥条件下木束内部自由水和吸着水的驱动力及其移动特性。研究表明:①高温干燥中自由水的移动为毛细管压力下液体的团块迁移和在压力梯度下的水蒸汽迁移,建立了高温干燥过程中自由水迁移量计算方程。②高温干燥中吸着水的扩散移动为浓度梯度引起吸着水的扩散和在水蒸汽压力梯度下的水蒸汽扩散迁移,更多还原

【Abstract】 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更多还原