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Hydrodynamics studies on macro- and micro-flow structure with effects of particle properties in a circulating fluidized bed.

机译：循环流化床中宏观和微观流动结构的流体动力学研究，以及颗粒性质的影响。

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摘要

A systematic and comprehensive hydrodynamics study was conducted in a narrow rectangular circulating fluidized bed (2-D CFB) to investigate the effects of particle properties on the characterization of macroscopic and microscopic flow behaviors. The CFB system consisted of a 7.6 m riser with a 19 mm x 114 mm cross section and a downcomer with a large storage section at the top. FCC, glassbeads and sand particles were employed to study the effect of particle density, size and sphericity. Differential pressure measurement, optical fiber probe and visualization technique were applied. Experimental results were examined focusing on the solids distribution for the different types of particles. The particle aggregation was also investigated involving the mechanisms of cluster formation and characteristics of particle aggregates.;The characteristics of microscopic flow were studied with the same types of particles as for the macroscopic flow study in the CFB riser under various operating conditions. A new digital imaging system consisting of a high-speed video camera, light source and image process programs was designed and developed to enable the high density fast flow to be visualized directly, particularly focusing on the particle aggregations. The particle aggregates were characterized by analyzing the images frame by frame and were classified into different form types. A new model was proposed to predict the form of cluster in the fully developed region. The instantaneous solids concentration data obtained by the optical fiber probe were also investigated to identify particle aggregates and characterize the cluster properties. The effects of particle properties on the characteristics of clusters, including the cluster forms, number fraction, time fraction, cluster frequency and mean existence time, were studied. A new method was proposed and realized the measurements of cluster velocity and size with the solids concentration signals detected by the optical probes. The results indicated the smaller and lighter particles have higher tendency to aggregate than the larger and heavier particles. The particle properties were also considered as factors influencing the cluster velocity and size.;This research combined the intrusive and non-intrusive measurements to study the macro- and micro-flow structure in the CFB riser. The obtained results agreed well with others derived from different measurement techniques. Furthermore, to a great extent, the studies of the two scopes are supportive for each other.;Keywords: Rectangular Circulating Fluidized Bed, Macroflow, Microflow, Particle properties, Visualization, Optical fiber probe, Solids concentration, Particle velocity, Particle aggregation, Cluster velocity, Cluster size;The macroscopic flow structure in the CFB riser was studied over a wide range of operating conditions with five types of particles. Extensive experiments were carried out using an optical fiber probe system, which can measure the solids concentration and particle velocity simultaneously. The results showed the lateral and axial profiles of solids concentration and corresponding particle velocity were influenced by the particle properties as well as operating conditions. The influences of particle density, size and sphericity on the solids concentration and particle velocity were studied in detail. It was found that the heavier particles had denser solids distribution and lower particle velocity profiles laterally and axially. The larger particle size led to a higher solids concentration and slower particle acceleration as well as a lower particle velocity along the entire riser. The particle sphericity influenced the solids distribution by increasing the solids concentration and decreasing the particle velocity with the increase of particle sphericity. The effects of riser geometry, distributor design and operating condition on the solids distribution were also studied. To achieve a good understanding of the mechanism for the particle properties to affect the flow, the slip velocity and the force balance for particles moving in gas was investigated. Correlations between the local particle velocity and solids concentration were proposed to work for each type of particles and to indicate the influence of particle properties on the solids distribution.
机译：在狭窄的矩形循环流化床（2-D CFB）中进行了系统的综合流体力学研究，以研究颗粒性质对宏观和微观流动行为表征的影响。 CFB系统由一个7.6 m的立管，一个横截面为19 mm x 114 mm的降液管和一个在顶部具有较大存储段的降液管组成。使用FCC，玻璃珠和沙粒来研究颗粒密度，尺寸和球形度的影响。应用压差测量，光纤探头和可视化技术。检查了实验结果，重点研究了不同类型颗粒的固体分布。还研究了颗粒团聚，包括团簇形成的机理和颗粒团聚体的特征。；在相同的颗粒类型下，研究了与CFB立管中各种工作条件下的宏观流研究相同类型的微观流特征。设计并开发了一种新的数字成像系统，该系统由高速摄像机，光源和图像处理程序组成，可直接可视化高密度快速流动，特别是关注颗粒聚集。通过逐帧分析图像来表征颗粒聚集体，并将其分类为不同的形式类型。提出了一个新的模型来预测完全发达地区的集群形式。还研究了由光纤探针获得的瞬时固体浓度数据，以识别颗粒聚集体并表征团簇性质。研究了颗粒性质对团簇特征的影响，包括团簇形式，数量分数，时间分数，团簇频率和平均存在时间。提出了一种新的方法，并利用光学探针检测到的固体浓度信号实现了团簇速度和团簇的测量。结果表明，较小和较轻的颗粒比较大和较重的颗粒具有更高的聚集趋势。颗粒的性质也被认为是影响团簇速度和大小的因素。本研究结合了侵入式和非侵入式测量方法，研究了CFB立管中的宏观和微观流动结构。所得结果与其他源自不同测量技术的结果非常吻合。此外，这两个范围的研究在很大程度上是相互支持的。关键词：矩形循环流化床，大流量，微流，颗粒性质，可视化，光纤探针，固体浓度，颗粒速度，颗粒聚集，聚类速度，团簇尺寸；研究了CFB立管中的宏观流动结构，研究了五种类型颗粒的广泛运行条件。使用光纤探针系统进行了广泛的实验，该系统可以同时测量固体浓度和颗粒速度。结果表明，固体浓度和相应的颗粒速度的横向和轴向分布受颗粒性质以及操作条件的影响。详细研究了颗粒密度，尺寸和球形度对固体浓度和颗粒速度的影响。发现较重的颗粒在横向和轴向上具有较稠密的固体分布和较低的颗粒速度分布。较大的颗粒尺寸导致较高的固体浓度和较慢的颗粒加速度，以及沿整个提升管的较低颗粒速度。随着颗粒球形度的增加，颗粒球形度通过增加固形物浓度和降低颗粒速度来影响固体分布。还研究了立管几何形状，分配器设计和操作条件对固体分布的影响。为了更好地理解颗粒性质影响流动的机理，研究了气体中颗粒运动的滑移速度和力平衡。提出了局部颗粒速度和固体浓度之间的相关性，以适用于每种类型的颗粒，并指出颗粒性质对固体分布的影响。

著录项

  • 作者

    Xu, Jing.;

  • 作者单位

    The University of Western Ontario (Canada).;

  • 授予单位 The University of Western Ontario (Canada).;
  • 学科 Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 317 p.
  • 总页数 317
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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