【作者】 曹石林；

【导师】 谢拥群； 陈礼辉；

【作者基本信息】 福建农林大学 ， 木材科学与技术， 2003， 硕士

【摘要】 对撞流干燥是一种目前国内外正在研究开发的新型干燥方法。它利用相向气流对撞所形成的高度湍流以及湿物料颗粒在对撞区内的快速非稳态运动来显著增强传热传质过程，使湿物料在极短时间内完成干燥。因而，对撞流干燥具有快速、高强度干燥的特点，并能很好地保持产品的品质。但迄今为止，对于对撞流干燥系统的流动与干燥特性的研究在国内外仅有个别学者涉及，而把对撞流干燥技术引入到刨花等林产品的干燥更是一个全新的课题。因此，开展刨花对撞流干燥的实验研究具有重要的学术意义和实用价值。 在本文中，为了探求刨花对撞流干燥的干燥特性、对刨花品质的影响及其动力学规律，进行了以下三个方面的研究： 首先，在不同气流温度、湿度、流量及不同刨花初含水率、载带率条件下进行刨花对撞流干燥实验。研究结果表明，随着气流温度的升高、气流湿度的下降、气流流量的增加、刨花初含水率的提高及载带率的减小，刨花对撞流干燥的强度也随着提高。特别地，气流质量流量的增加和载带率的减小能显著地提高干燥强度，而相比之下，气流湿度、气流温度影响并不显著。 其次，把刨花用传统气流干燥和对撞流干燥二种干燥方式干燥后分别压制成刨花板，然后检测刨花板的力学性能，并对不同干燥方式干燥而成的刨花进行数码显微切片观察。研究结果表明，对撞流干燥对刨花的外部形态和内部纤维结构都没有造成破坏。 最后，测量了气流速度、刨花速度、刨花与气流间的相对速度、刨花在半环内的停留时间及刨花在半环内沿径向和周向的速度分布，并在实验基础上进行了刨花对撞流干燥的动力学分析。研究结果表明：由于受到离心力的作用，使刨花在环形管道内靠外壁面的一侧局部浓度增大，导致刨花制动，速度减小，从而气流与刨花之间的相对速度增大，传热传质速率提高；刨花速度在沿运动方向的变化是，在半环内起始加速段迅速增大，随后增大趋于平缓，最后达到最大；随着气流速度的增大和载带率的减小，刨花颗粒在半环内的振荡次数增加，停留时间延长。 总之，对撞流干燥技术是一种优良的刨花干燥方式，具有良好的应用前景。本文试图通过以上的研究为刨花、纤维、纸浆等林产品的对撞流干燥工艺参数的制定和干燥装置的工程设计提供理论和实验依据，并为进一福建农林大学硕士研究生学位论文论文题目:木材刨花对撞流干燥的实验研究步实现刨花等林产品对撞流干燥的工业化生产奠定基础。更多还原

【Abstract】 Impinging stream drying (ISD) is a new drying method that is being studied presently. It can significantly improve the heat and mass-transfer process by the deep turbulence made by the impinging of the opposite streams and the rapid and unstable movement of wet particles and finish drying process of wet materials in a very short time, so, ISD bears the characteristics of drying rapidly and in a high-intensity and maintaining the quality of materials. But so far, the flow and drying characteristics of ISD still have been studied by only a few researchers. Moreover, it is a completely new field that wood particles are dried by ISD. Therefore, experimental study on impinging stream drying of wood particles bears important academic significance and practical value.In this article, the following three researches are accomplished to discover the drying characteristics, influence on the quality of wood particles and kinetic rules of ISD:First, experimental study on the influence of air temperature, velocity, initial moisture content of wood particles and mass flow rates ratio on the process of ISD has been performed. The test results show that the performance of ISD will improve with the increase of air temperature, mass flow of air and initial moisture content of wood particles and the decrease of air humidity and mass flow rates ratio. In particular, the increase of air temperature and the decrease of mass flow rates ratio can improve the performance of ISD remarkably. The influence of air temperature and humidity isn’t remarkable in comparison.Next, the performances of particle-board made of wood particles dried through the two different methods: the traditional air drying and the ISD, are measured, and the fibrous structure of wood particles is observed by digital microscope. The results indicate that the exterior shape and the interior fibrous structure of wood particles aren’t broken after dried by ISD.Finally, the air velocity, the velocity of the wood particle, the relative velocity between the air and the wood particle, the wood particle’s residencetime and the variations of the particle’s velocity along radial and circle are measured. The ISD of wood particles is analyzed on dynamics. The results indicate: the concentration of wood particle near the outside wall of the annular pipe increase under the effect of centrifugal force. It slows the particle down, thus increases the relative velocity between the air and the wood particle, which causes the speed of heat and mass-transfer increase. The velocity of the wood particle increases rapidly at the moment of acceleration, then goes up steadily, reaches the maximum at last. The surge time of the wood particle increases and the residence of the one prolongs in the semi-circle with the increase of air velocity and the decrease of mass flow rates ratio.In a word, ISD is a good method of drying particle and bears a wonderful prospect. The article tries to provide the academic and experimental basis for establishment of technological parameters, design of the equipment and industrialization of ISD of wood particle, fibre and pulp etc forestry products.更多还原