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基于双峰速度分布的动理学理论及其在双颗粒混合物与气固流态化中的应用
梅一枫
学位类型硕士
导师王维 ; 陈延佩
2016-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词气固流态化 颗粒动理学理论 介尺度结构 能量非均分 双峰分布
摘要

气固流态化系统是典型的非线性非平衡系统,其中存在以团聚物为代表的非均匀结构。非均匀结构对系统内气体和颗粒的流动有显著的影响,对它的准确描述因而是建模成功的关键。基于传统颗粒流动理学理论的双流体模型没有包含非均匀结构,而由于颗粒团聚物的存在,可以将非均匀结构简化为稀密两相结构处理。假设稀相和密相的颗粒各自具有不同的颗粒温度和平均速度,则固相总速度分布形成的双峰分布能够很好地反映气固流化床能量非均分、非麦克斯韦速度分布的特征。基于这个双峰速度分布,从研究微观颗粒运动的波尔兹曼方程出发,论文推导了新的动理学理论,并进一步得到了考虑非均匀结构的多流体模型。第二章首先推导了混合双颗粒的动理学理论。对混合双颗粒系统,本章推导了应力应变关系等传递系数的表达式。结果显示新的动理学理论得到碰撞频率和应力应变关系比之前的结果更符合系统的物理特性。第三章包含了混合双颗粒动理学理论的两个应用和验证:第一个是预测混合颗粒简单剪切流中两种颗粒的温度,我们的理论预测结果与DEM模拟的结果一致;第二个是在边壁振动的颗粒系统中预测颗粒的自由程。通过将颗粒分为沿正方向和负方向运动的两族颗粒,本文的预测结果与DEM模拟的结果一致。上述结果皆比传统动理学理论结果更优。第四章中,混合颗粒的动理学理论被应用于气固流态化系统,形成了一个新的双流体模型初步方案。第五章对本文进行了总结,并对未来流态化模拟及动理学的研究进行了展望。

其他摘要

Gas-solid fluidized systems are typical nonlinear non-equilibrium systems. Inside such systems, particles aggregate and form meso-scale structures such as non-uniform clusters. The meso-scale structures have significant effects on the momentum transfer of gas and particles. Accurate description of these non-uniform structures is hence very important to successful mathematical modeling of fluidization. However, the two-fluid model based on traditional kinetic theory of granular flow does not take into account the non-uniform structures present in gas-solid fluidized systems. Moreover, based on the clustering behavior of particles, it is reasonable to simplify the non-uniform structure into a dilute-dense two-phase description. By assuming that particles in the dilute and dense phases have different granular temperatures and mean velocities, the solid phase as a whole will exhibit a bimodal velocity distribution which well reflects the non-Maxwllian and energy nonequipartition features of gas-solid fluidization. Based on the bimodal distribution, a new kinetic theory is derived and further employed to build a structure-based multi-fluid model.In Chapter 2, we developed the kinetic theory of binary granular mixture, which can be viewed as a generalization of gas-solid fluidized system with dilute-dense structure if the exchange between the dilute and dense phases can be well considered. Transport terms like the stress-strain relationship are derived for binary granular mixture. The results show that the collision frequency and stress-strain relationship derived from the new kinetic theory are in better accordance with the characteristic of binary granular mixture than previous results.Chapter 3 presents two applications of the kinetic theory of binary granular mixture. The first application is the calculation of granular temperature of mixed particles in a simple shear flow. The result of numerical computing is consistent with the results of molecular dynamics or DEM simulation. The second application is the prediction of the free path of particles in the context of a vibro-fluidized granular system. We divide the particles into two species, one consisting of particles moving towards positive x-direction and the other towards negative x-direction. The results developed in Chapter 2 are used to predict the free path of particles. The results agree well with the DEM simulation of the vibro-fluidization system. In Chapter 4, we propose a psedo-fluid model based on kinetic theory of binary mixture. Particles in the dilute and dense phases are regarded as two different particle species. The kinetic theory of binary mixture with addition of exchange terms is used subsequently to determine the transport coefficients. At last, Chapter 5 summarize the thesis and gives prospects for study of fluidization modeling and kinetic theory in the future. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/22867
专题研究所(批量导入)
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梅一枫. 基于双峰速度分布的动理学理论及其在双颗粒混合物与气固流态化中的应用[D]. 北京. 中国科学院研究生院,2016.
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