【作者】 谢拥群；

【导师】 张璧光； 常建民；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2003， 博士

【摘要】 对撞流干燥技术是一项具有很强干燥能力的新技术，它在粮食及化工等领域已有许多研究和一些工业应用，但它在木材加工领域的研究和应用，目前尚属空白。木材碎料的干燥是人造板生产中能耗很大的工序之一，将对撞流干燥技术应用于这一环节对于生产过程的节能降耗和提高生产效益方面将起到重要作用。因此本项目的研究既有重要的理论价值，更有实际应用的意义。 本项目首次建立了可用于木材碎料干燥的“垂直---倾斜半环组台式干燥实验装置”，并进行了木材纤维和刨花的干燥实验。分析了各种因素对干燥过程和效果的影响。实验表明：木材纤维初含水率对产品终含水率影响很小，在不同初含水率的情况下均能得到符合生产要求的纤维原料；木材刨花的初含水率对终含水率有较大的影响，当含水率高时无法一次干燥得到符合含水率的原料，必须进行第二次循环干燥。气流温度和流量对提高系统的能力有明显的增强作用，它们是干燥能力改变的重要影响因素；在带载率增加的情况下，干燥后的终含水率略有增加，系统的去水能力随着带载率的提高几乎线性地相应提高。可以适当地加大带载率以提高系统的生产能力。 本文从微观观察到制成品性能的宏观分析，研究了对撞流干燥对产品质量的影响。研究表明：对撞流干燥技术对木材碎料的干燥，在材料微观结构上没有任何损伤的现象。常规干燥和对撞流干燥的原料在相同条件下制成的产品的性能测试分析显示两者之间没有明显的差别。 实验中还进行了系统温度分布、物料沿运动方向的含水率变化情况、系统压降等测试，为系统分析和研究提供了第一手资料。研究了各种组合情况下的干燥效果，以及各对撞干燥器所起的作用。实验表明对撞流干燥器和普通气流干燥相比，其能力明显提高，它达到了相同系统参数下常规气流干燥无法达到的效果。 本文首次通过理论分析和近似实验初步研究了木材干燥过程中的热质耦合现象。修正了木材干燥相关教科书中对于热质传递关系的描述，导出了相应的关系式。文中利用电路电阻的类比分析的方法，推导了木材刨花横向导热系数。取得了经过实验修正的理论公式，计算了16种树种的导热系数，并与公开发表的实验值进行比较。最大误差为8.7％，平均误差4.8％。摘要 文中在分析了物料在对撞流干燥系统中的运动学特性、木材内部水分分布特性和传热传质特性的基础上，借鉴了当前国内外在木材碎料干燥中的最新研究成果，建立了包括对撞流干燥器在内的系统数学模型。计算和实验结果对比表明:这一系统模型基本上反映了系统干燥的全过程，可以应用于对撞流干燥系统的研究和分析，并可以用于指导此类干燥系统的设计一。更多还原

【Abstract】 Impinging stream drying technology is a new drying technology with, high drying capacity. Many studies have been made on its theory and application on food and chemical industries. However, few have been reported on its study and application in wood industry. Drying of wood particle is the most energy consuming process in whole production of wood-based panel, and impinging stream drying technology will play an important role in energy saving and benefit improvement in the process of drying wood particle. Therefore, the study of this project is of important theoretical value and practical significance.To study the applicability of impinging stream drying technology in drying wood particulate, the Vertical-inclined semi-circular Impinging Stream Drying System was built to dry wood particulate materials, and drying trials were done for wood fiber and wood particle respectively. Also effects of various factors on drying process and drying efficiency were examined. These factors include: initial moisture content, airflow temperature and flux, and load. The experience results indicate that there is little effects of the initial moisture content of wood fiber on the final moisture content, i.e., fiber meeting the required final moisture content can be obtained even if materials contain different initial moisture content. However, the initial moisture content of wood particle has greater effect on the final content, and wood particle with high initial moisture content could not reach the required final moisture content through one dryingprocess, so that more drying processes may be needed. The results also suggest that only wood particle with moisture content near fiber saturation point can reach the required final moisture content after one drying process, and ail’flow temperature and flux can improve the drying capacity significantly. With the load increasing, the final moisture content goes up slightly, and the ability of system removing moisture rises linearly with the increasing of load. Therefore, raising load is an effective way to improve system throughput.As a new high speed drying technology, the wood particulate quality through impinging stream drying system is the most concern. In the thesis, both microscopic inspection and product properties were analyzed. The results indicate that no scathes are found in microscopic structure of material dried under impinging stream drying system. F-test shows that there are no significant differences between the properties of products produced under same conditions but materials dried under different systems, i.e., impinging stream drying system and conventional drying system. Therefore, we may draw conclusion that impinging stream drying technology may be employed to effectively dry wood particulate with less energy consummation and no negative effects on product quality.Also tested were temperature distribution, changes of moisture content along the direction of material movement, pressure drops of system, drying effects of various parameter combinations. Test outcomes demonstrate that drying capacity of impinging stream drying system is considerably higher than that of conventional airflow drying system.Impinging drying of wood is a process of moisture removal with high speed and efficiency, so that moisture diffusion and movement, heat transfer from drying media tomaterial are very prompt. As a result, the coupling effect of heat and moisture might affect drying process. The thesis testified the existence of such a coupling effect theoretically and nearly experimentally, and revised the description of the heat transfer and mass diffusion in related textbooks, and educed the relationship formula about relationship of heat transfer and mass diffusion during the wood being dried. In order to examine the characteristics of heat transfer in wood particle, an analogy approach of computing resistance of electro-circuit was employed in deriving transversal heat conductivity of wood particulate. The correction coefficients for uneven material distrib更多还原