论文总字数：35493字

摘 要

纳米颗粒具有独特的光学、磁学、电学和热力学等特殊的物理化学性质，广泛应用于许多有前景的工业。气固流态化技术能规模化地对纳米颗粒进行混合、输送及制备处理，显著提高纳米粉体处理效率及传热和传质速率。但纳米颗粒间存在较强的粘附力易形成聚团，导致其流化特征与常规颗粒不同。

本文对来自两个供应商，编号分别为VK细粒和DK细粒的物料进行流化实验研究。实验分为两阶段，第一阶段是探究VK细粒（原生粒径为30nm）在不同振动工况下其流化特性的变化规律；第二阶段为探究不同原生粒径的DK细粒和VK细粒的物性参数与流化特征的关系以及有振动（20Hz、1mm）、无振动下的流化效果。

实验第一阶段：VK-SiO₂纳米颗粒在传统流化床中随着气速增大其流化行为分为比例段、屈服段、鼓泡流化段、湍动流化段和飞溅段。VK-Al₂O₃流化效果较差，稳定流化时表现为鼓泡流态化，无湍动流化段；两种颗粒的流化在施加振动辅助后都可以抑制沟流并减少底部大颗粒聚团的聚积，大幅度降低临界流化速度。不同振动工况下，流化有不同程度的改善效果。VK-Al₂O₃在低振幅下（A=0.5mm），振频的增加对流化效果的改善作用不大，VK-SiO₂在振频大于20Hz，振幅大于1.5mm时，增加振幅无法进一步加强改善流化效果。本实验中，VK-SiO₂的最佳振动工况为f=30Hz，A=1mm。而VK-Al₂O₃因实验局限未测出其最佳工况。VK-SiO₂流化时，增加振动强度导致床层压缩，膨胀比降低。而对于VK-Al₂O₃，增加振动强度可以加强底部大聚团破碎作用，提高膨胀比。

实验第二阶段：即使同类型颗粒，不同供应商的物料所表现的流化特性不同。对于不同原生粒径的VK细粒和DK细粒，分别对比其物性参数和流化特征发现：DK颗粒随原生粒径的增大，安息角变小，HR值（振实密度与堆积密度之比）变大，颗粒的流化效果变好；VK颗粒随粒径的增大，安息角变大，HR值变小，颗粒的流化效果变差；不同原生粒径的VK和DK细粒在有（20Hz、1mm）振动、无振动工况下流化实验对比发现：振动均能改善流化效果，但随着粒径的增大，振动能对颗粒流化的改善幅度明显减小。

1. 关键词:纳米颗粒，流化特征，物性参数，振动流化床

Abstract

Nanoparticles have special physical and chemical properties such as optics, magnetism, electricity and thermodynamics and are widely used in many promising industries. The gas-solid fluidization technology can be used for mixing, transportation and preparing nano-particles in a large scale, which can significantly improve the efficiency, heat transfer and mass transfer rate of nanoparticles. However, the strong adhesion force between nanoparticles is easy to form agglomerates, which results in different fluidization characteristics from conventional particles.

The particles from two suppliers which name VK and DK respectively in this paper. The experiment is divided into two stages. The first stage is to explore the fluidization characteristics of VK particles (primary particle size is 30nm) under different vibration conditions. The second stage is to explore the relationship between the physical parameters of DK fine particles and VK fine particles with different initial particle sizes, and the fluidization characteristics.

The first stage of the experiment: The VK-SiO₂ particles flow with the superficial gas velocity increases, the proportion is divided into segments, yield, bubbling, turbulent flow zone and splash period of five stages in the traditional fluidized bed. VK-Al₂O₃ fluidization effect is poor, and the steady flow keep bubbling fluidization and no turbulent flow. In the vibration fluidization experiment, the accumulation of agglomerates in the bottom of the bed can be reduced, the throttling and gully flow can be restrained, and the critical fluidization velocity can be greatly reduced. The fluidization of particles can be improved to different degrees with different vibration conditions. The increase of vibration frequency has little effect on the improvement of VK-Al₂O₃ fluidization effect at low amplitude (A=0.5mm), and the increase of amplitude cannot further enhance the VK-SiO₂ fluidization effect when the vibration frequency is greater than 20Hz and amplitude is greater than 1.5mm. In this experiment, the optimal vibration condition of VK-SiO₂ is f=30Hz,A=1mm. However, VK-Al₂O₃ was not detected due to experimental limitations. During VK-SiO₂ fluidization, the bed layer will be ampressed and reduce the expansion ratio when the vibration strength increase. In contrast, when VK-Al₂O₃ is fluidized, the increase in vibration strength can enhance the role of large agglomerates at the bottom of the bad and incerase the expansion ratio.

The second stage of the experiment: Even with the same type of particles, different suppliers have different fluidization characteristics.. The experimental results show that the fluidization effect of the DK particles gets better, the rest Angle becomes smaller and the HR value becomes larger with the increase of the primary particle size. However, the experimental results of VK particles are contrary to DK particles. The vibration fluidization (20Hz, 1mm) experiments of VK and DK particles with different primary size showed that the effect of vibration on particle fluidization decreased obviously with the increase of particle primary size.

KEY WORDS: nanoparticles, fluidization characteristics, vibrating fluidized bed, physical parameters

目 录

摘 要 I

Abstract II

目 录 III

第一章 绪论 1

1.1课题研究背景 1

1.2粉体的分类 1

1.3粉体的流动性传统表征方法及其影响因素 3

1.3.1安息角法 3

1.3.2 Hausner指数法 3

1.3.3 粉体流动特性影响因素 4

1.4 纳米颗粒的流化性质 4

1.4.1 颗粒间的粘附力 4

1.4.2 颗粒流态化的表征 5

1.4.3 颗粒流态化质量的预估判据 5

1.5 振动场对纳米颗粒流态化的改善作用 6

1.6 选题意义和研究内容 7

1.7 本章小结 7

第二章 实验与方法 8

2.1实验物料 8

2.2实验研究方法 10

2.2.1物料物性参数测试方法 10

2.2.2物料在振动流化床中流化特性测试方法 11

2.3 本章小结 12

第三章 振动对纳米颗粒流态化影响 13

3.1无振动下纳米颗粒流化特征的对比分析 13

3.2 不同振动参数纳米颗粒流化特征比较分析 16

3.2.1 振动流化床的工作机理 16

3.2.2 振幅对纳米颗粒流化特征的影响 16

3.2.3 振频对纳米颗粒流化特征的影响 20

3.3 本章小结 22

第四章 不同物料的物性参数与流化特征 24

4.1 不同粒径纳米颗粒物性参数与流化特征 24

4.1.1 DK颗粒的物性参数与流化特征 24

4.1.2 VK颗粒的物性参数与流化特征 27

4.2 不同原生粒径纳米颗粒振动流化特征差异 28

4.2.1 不同粒径下DK颗粒振动流化特征差异 28

4.2.2 不同粒径下VK颗粒振动流化特征差异 29

4.3 本章小结 30

第五章 总结与展望 31

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