颗粒流体系统中聚团的形成过程与结构特征研究

发布时间：2018-01-01 23:24

本文关键词：颗粒流体系统中聚团的形成过程与结构特征研究　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年硕士论文　论文类型：学位论文

【摘要】：颗粒流体系统是一个具有时空多尺度结构的复杂系统,其中颗粒聚团是一种常见的非均匀结构。聚团的特性对于流化床等各类反应器的正常运行具有重要影响。目前对于聚团的研究大多针对尺寸和浓度分布等宏观统计性质,而对其形成过程与结构特征的研究非常有限。本论文利用离散颗粒模型(DPM)模拟了含有数百万个粘附性颗粒的液固体系,提出了一种适用于DPM模拟结果分析的聚团识别和量化方法。这种方法可以充分发挥DPM模拟能够精确量化任意时刻每一个颗粒的速度和位置的优势,从聚团的尺寸、形状、稳定性角度表征其结构特征;通过跟踪颗粒进入或离开聚团的状态量化聚团生长和破碎的过程,并从颗粒受力的角度探究其机理。在论文第一章的文献综述的基础上,第二章分析并确定了本论文中DPM的具体设置、模拟对应的实验装置及主要参数,进而在实验和模拟中均观察到了聚团现象。在实验可观测的反应器中心区域,颗粒平均速度与体积分数与模拟吻合良好。第三章提出了聚团的识别与量化方法,并以此探究了反应器厚度、进料状态、粘附力强度对模拟结果的影响,从尺寸、形状、稳定性三个角度考察了聚团的结构特征。研究表明,聚团内颗粒数可以有效表征聚团的尺寸,而聚团内颗粒的平均配位数及配位数分布可以表征聚团的形状,配位颗粒表面间的平均距离及颗粒在聚团内的平均停留时间可以表征其稳定性。第四章提出了量化聚团生长与破碎的方法,并以此分析模拟结果表明:这些过程存在渐进或突变两种方式,并以前者为主;而粘附力、曳力、碰撞力的非均匀分布能显著影响聚团的净变化率、尺寸和形状。第五章总结了全文工作并展望了今后的研究方向。
[Abstract]:Granular fluid system is a complex system with space-time and multi-scale structure. Particle agglomeration is a common nonuniform structure, and the characteristics of agglomeration have an important effect on the normal operation of various reactors such as fluidized bed. At present, most of the studies on clusters focus on macro systems such as size and concentration distribution. Calculated nature. However, the formation process and structural characteristics are very limited. In this paper, a discrete particle model (DPMM) is used to simulate a liquid-solid system containing millions of adherent particles. A cluster recognition and quantization method suitable for the analysis of DPM simulation results is proposed. This method can give full play to the advantages of DPM simulation which can accurately quantify the velocity and position of each particle at any time. The structure of the cluster is characterized by its size, shape and stability. By tracking the state of particles entering or leaving the cluster, quantifying the process of cluster growth and fragmentation, and exploring its mechanism from the point of view of the force of particles, based on the literature review in the first chapter of the paper. The second chapter analyzes and determines the specific setting of DPM in this paper, simulates the corresponding experimental device and main parameters. The particle average velocity and volume fraction agree well with the simulation in the center of the reactor. In the third chapter, the recognition and quantification methods of the cluster are proposed. The effects of reactor thickness, feed state and adhesion strength on the simulation results were investigated. The structure characteristics of the clusters were investigated from three aspects: size, shape and stability. The number of particles in the cluster can effectively characterize the size of the cluster, while the average coordination number and the distribution of the coordination number of the particles in the cluster can characterize the shape of the cluster. The average distance between the surface of the coordination particles and the average residence time of the particles in the cluster can be used to characterize the stability of the coordination particles. In Chapter 4th, a method of quantifying the growth and fragmentation of the clusters is proposed. The simulation results show that there are two modes of evolution or mutation in these processes, and the former is the main one. However, the non-uniform distribution of adhesion force, drag force and collision force can significantly affect the net change rate, size and shape of the cluster. Chapter 5th summarizes the full text and looks forward to the future research direction.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ021.1

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