【作者】 王迎慧；

【导师】 归柯庭；

【作者基本信息】 东南大学 ， 工程热物理， 2005， 博士

【摘要】 磁流化床利用外加磁场调节、控制床内的气固两相流动，可以实现鼓泡流化到稳定流化的转变，在磁稳流化状态下，流化床具有无气体短路、气固接触好、床层压降小、流通截面大等优点，弥补了常规流化床的不足，有望在环境保护、分离吸附、生物与化学反应等工业领域得到广泛地应用。深入、系统地研究磁流化床的气固两相流动的特征对指导磁流化床的工程设计、运行，促进磁流化床的应用推广有着十分重要的意义。本文首先从理论上建立了磁流化床气固两相流动的动力学模型。磁流化床中的气固两相流属于有磁场力作用的稠密气固两相流，故本文着重从解决磁流化床中气固两相之间的耦合作用出发，基于双流体模型，结合颗粒运动的动力学理论，构建出描述磁流化床气固两相流动特性的控制方程。它不但有效地解决了固相颗粒的湍动以及颗粒间的碰撞、摩擦等因素对气固两相流动的影响，而且考虑了气固两相之间湍动能的相互作用，更好地反映出气固两相的湍动对各自流场分布的影响。应用计算流体软件FLUENT对磁流化床气固两相流动进行数值模拟。数值计算主要考察磁场强度对气固两相流动的影响，本文通过对无磁场、弱磁场、适度磁场的两种粒径的颗粒分别在三种气体表观流速比的工况下的气固两相流动进行数值计算，得到反映其流动特征的固相体积浓度分布、床层压降分布。同时，将数值计算结果与实验研究获得的数据进行比对，证明了本文所建立的模型的适用性以及数值模拟预测结果的可靠性与准确性。为充分地掌握磁流化床气固两相流动的机理，在数值模拟的同时，本文还对磁流化床的流化特性进行了实验研究。实验中采用数字式差压传感器对床层压降及波动进行了测定，并以此确定出磁流化床颗粒流化的最小鼓泡流化速度，进而得到各工况条件下磁稳操作区域的范围。在实验研究的基础上，结合实验数据，对无量纲数Re、Ar、Er进行回归分析，得出确定磁稳区域的实验关联式。根据关联式可方便地给出磁稳流化床具体的运行参数，这对磁稳流化床的应用研究有着积极意义。研究磁流化床气固两相流动特征的目的就是为磁流化床的应用研究提供理论依据。本文在已有研究的基础上，面向工程应用，设计出具有一定实用价值的磁稳流化床除尘装置。设计中就装置的关键部件，如床体结构、布风板、磁场发生器、滤料再生系统等给出了优化设计方案，并对所设计的除尘装置的除尘性能进行了实验验证，分析得出了磁稳流化床除尘装置连续、高效运行的基本条件。更多还原

【Abstract】 It is convenient to achieve stable fluidization instead of bubbling fluidization by utilizing magnetically fluidized bed because of its advantage of controlling and adjusting. Furthermore, in magnetically stabilized fluidized bed, not only it can greatly improve the contact between gas and solid as result of no gas bypassing and particles’ backmixing, but also can it be with less pressure drop and higher gas velocity in the bed. And it will be widely come into use in many industrial fields, such as environmental protection, separation technology, biological or chemical reaction, and so on. Therefore, it is of great significance to study further and systematically on the characteristics of the gas-solid two phase flow in magnetically fluidized bed, and all results can also be used in the engineering design and operation.In this paper, a dynamic model of the gas-solid two phase flow in magnetically fluidized bed is established first. Because the gas-solid two phase flow in magnetically fluidized bed belongs to dense-phase flow with the influence of the magnetic force, the intercoupling between the two phase should be considered more carefully and completely. On the basis of two-fluid model, combining the kinetic theory of granular flow, the differential equations of describing the gas-solid two phase flow in magnetically fluidized bed are obtained. On one hand, it can effectively solve the interaction because of the particles’ turbulent flow, such as collision, friction and so on, on the other hand, considering the interaction of turbulent kinetic energy among the particles, the dissipation energy is introduced into the transportation equation of particles, and it can reflect the effect of the turbulence between the two phase well.Numerical simulation of the gas-solid two phase flow in magnetically fluidized bed is carried out, using FLUENT, a kind of software of computational fluid dynamics. It focuses on investigating the influence on the two phase flow due to varying magnetic field intensity. In the paper, no magnetic field, weak intensity and moderate intensity are computed for two kinds of particle with different diameters and three different ratios between gas superficial velocity （U_g） and initial bubbling velocity (U_mf) , and some results showing the characteristics of the gas-solid two phase flow in magnetically fluidized bed are obtained, including the distribution of the solid phase, pressure drop of the bed. Compared with the experimental data, it demonstrates that the results of the numerical simulation based on the dynamic model coincide with the experimental data well.In order to understand the mechanism of the gas-solid two phase flow in magnetically fluidized bed further, an experimental research to reveal the characteristics of magnetically fluidized bed is also carried out. In the experiments, the bed pressure drop and its fluctuation are measured by using digital sensor of pressure. And the minimum bubbling velocity is determined on the basis of the bed pressure drop and its fluctuation. To be further, the stable zones on different operational conditions in magnetically stabilized fluidized bed are obtained. Finally, on the basis of all experimental research, a relationship calculating the stable zone using three dimensionless factors, Re, Ar and Er is put forward, and it is more convenient to provide the operational parameters in practice. Consequently it is very helpful to promote the application of magnetically stabilized fluidized bed.All study on the characteristics of the gas-solid two phase flow in magnetically fluidized bed is to develop the application of magnetically fluidized bed better. On the basis of the study discussed above, a facility removing the dust in gas stream is designed for industrial application. The key components, for instance, bed structure, air distributor, magnetic field generator, and particles-regenerating system are designed in detail in the paper. Then the facility’s performance of collecting dust is verified by the experiment, and in the meantime, the operational parameters for high efficiency of the facility are also concluded.更多还原