纳米级SiO2颗粒流化床的塌落行为

在直径为 35mm的小型流化床中考察了纳米级SiO₂ 颗粒 (商品牌号R972 )的床层塌落行为 .该种经过表面改性的颗粒可以通过自团聚形成稳定、均匀的聚团散式流化 .实验证明 ,这种颗粒的床层塌落行为明显不同于普通的GeldartA类与C类颗粒 ,其塌落过程可分为恒速沉降阶段和减速压实阶段 .通过对塌落速率的分析 ,提出了聚团散式流化的床层塌落机制     

粘附性颗粒流态化研究进展

主要阐述了粘附性颗粒流态化特性（初始流化速度、床膨胀、塌落）及聚团流化过程,提出了粘附性颗粒流态化的机理是聚团流化．并对近年来国内外在预测聚团大小、床层结构模型、改善粘附性颗粒流化性能方面的研究进展进行了总结．     

C类颗粒添加纳米细粉后的流态化行为研究

为了研究纳米添加剂对细粉颗粒流化行为的影响,实验选用全床压降、最小流化速度、床层膨胀率、床层塌落曲线等表征细粉颗粒的流化特征。在直径为5.08 cm的小型流化床中研究了纳米添加剂SiO_2 (商品牌号R972)对细玻璃珠颗粒(Geldart A和C类颗粒)流化行为的影响。结果表明加入纳米添加剂后,C类颗粒的流动性得到明显的改善。与GeldartA类颗粒相比,经过表面改性的C类颗粒全床和浓相膨胀率更高,意味着更好的气固接触模式;在相同表观气速下,C类颗粒的流化更均匀,散式化程度更高。以上的发现对于C类颗粒的工业应用具有重要意义。     

超细颗粒表面改性后床层塌落行为研究

在直径为56mm的磁流化床中采用小粒径SiO2颗粒对微米级淀粉颗粒进行包裹，在鼓泡流化床中考察包裹后淀粉颗粒的床层塌落行为。实验表明，包裹后淀粉颗粒的床层塌落行为不同于未包裹的淀粉颗粒和Geldart A类颗粒。包裹后淀粉颗粒间粘性力减小，床层滞气能力降低，床层塌落高度增加，揭示磁流化床包裹实验中客体颗粒SiO2存在合适添加比例．证明表面改性是改善超细颗粒流化行为的有效手段。     

原生纳米级颗粒的聚团散式流态化

在内径为 35mm的小型玻璃流化床中考察了平均原生粒径为 16nm的SiO₂ 颗粒的流化行为 .实验发现 :当操作气速远远超过原生纳米颗粒的最小流化气速时 ,这种超细颗粒可以通过自团聚实现稳定、均匀的散式流化 ,并可获得比GeldartA类颗粒更高的床层膨胀比和更宽的散式操作区 .由于原生纳米级SiO₂ 颗粒在流化时形成的团聚物具有较大的粒径和很小的密度 ,使得该气固体系的流化行为与液固体系有许多相似之处 ,该过程对于研究气固流态化的散式化具有重要意义     

锥形流化床内碳纳米管的膨胀特性研究

流化床是碳纳米管宏量制备的一个关键设备,本文对100 mm管径无分布器式锥形流化床内的碳纳米管进行了床层膨胀研究的实验。通过对两种碳纳米管流化特性的观测分析,结果发现:对于垂直阵列管,存在分部流化的特性,对于聚团管,存在小颗粒迁移流化的特性。对初始床层高度为150,170,190 mm的流化床内的碳纳米管进行研究,在不同初始床层高度的情况下,不同种类的碳纳米管的膨胀行为和压力信号存在明显的差异,实验表明,在相同流速下,随着初始床层的增加,床层压降增加、初始流化风量和完全流化风量增加,膨胀率降低。     

一个基于双流体理论预测三维流化床内流动特性的数学模型(Ⅰ)气固体系散式或鼓泡流态化特性

将考虑拟平衡状态下颗粒与流体相互作用的附加力添加到基于双流体理论动量方程的数学模型中,用于Geldart A类物料散式流态化和B类物料鼓泡/床层塌落特性的三维数值模拟。该模型主要特点是将表征颗粒离散属性的特征长度视为颗粒直径的同一数量级且只需曳力系数一个关联式来封闭控制方程。在商业软件CFX4.4平台上,通过增加用户自定义子程序模拟了长0.2 m、宽0.2 m和高0.5 m流化床内瞬态流动特性。为了检验数学模型的实用性和数值模拟的可靠性,首先考察了两种A类物料在表观气速为u_mf和1.5u_mf下的散式流态化特性,结果展示出床层均匀膨胀的固有属性。随后,考察了扰动对A类物料在网格尺度上的局部空隙率和固体速度分布以及在设备尺度上床层压降的影响,探索了B类物料在网格尺度上鼓泡和床层塌落以及在设备尺度上鼓泡过程中床层压降和塌落过程中平均床层高度和相界面标准偏差的动态特性。上述模拟结果与经典的Geldart理论、前人的实验或模拟结果相吻合,说明该模型可以用来预报三维气固流化床内A类物料散式流态化和B类物料鼓泡及塌落的时空特性。     

纳米SiO2在添加磁性大颗粒磁场流化床中的流态化

研究了纳米SiO2在添加磁性大颗粒磁场流化床中的流化性能,实验中通过测量其床层膨胀曲线、床层压降曲线以及塌落曲线表明:磁性大颗粒在交变磁场下的振动作用可以破碎流化床中纳米SiO2的大聚团.使床层压降和床层膨胀明显增大,流化质量获得显著提高.实验同时考察了磁场强度、磁性颗粒的添加量以及不同的静床高度等参数对流化性能的影响.获得了最佳工艺操作条件.     

超细粉流化机理和团聚现象的探讨

在直径60mm的流化床中，以SiO2和TiO2超细粉为原料，考察了粉体物性、粉体填充状态和空气湿度等因素对超细粉流化行为和聚团性质的影响，结果表明：超细粉的流态化经历了活塞流、过渡区和聚团流化3个阶段；聚团的流化行为与大颗粒相似；初始填充状态对超细粉流化行为和聚团大小有重要影响，松填充有利于减小聚团尺寸和减少颗粒夹带，提高流化质量；并结合粉体层受力分析，对超细粉的流化机理和团聚现象进行了探讨。     

喷动─流化床流动特性的试验研究

分析了两种窄筛分Ｄ类颗粒在不同喷动－流化操作条件下的床层行为特征及床层总气流阻力，研究了平底型三维喷动－流化床内的气体流动模式，从而导出在固定床阶段床层总气流阻力的表达式，得出喷动－流化操作具有优越性的结论。     

大颗粒流态化特性的实验研究

通过对大颗粒流化曲线及床层高度的测试对大颗粒流化床的流化过程进行了研究。结果显示,大颗粒的流态化过程是一个渐进的过程,整个流化过程可以分为:床层高度恒定、颗粒位置调整、表面颗粒运动、节涌波动和完全流化5个阶段。由于颗粒自身特性的影响,导致大颗粒流化过程中的各个特征速度(如起始鼓泡流化速度和完全流化速度)产生了有别于小颗粒流化床的特性。     

Experimental profiles of lateral mixing of feed particles in a three‐dimensional fluidized bed

Solids mixing data of high quality is one of the most crucial steps for quantitative studies, but it is a difficult task to obtain in a fluidized bed especially with a 3D configuration. Therefore a novel sampling technique is developed with bed collapse method, for measuring lateral mixing of feed particles in a 3D fluidized bed. The sampling tool is designed using a “bottom‐to‐top sampling” idea. Its development, configuration and measurement repetition are discussed in detail. The effects of mixing time, fluidizing gas velocity, and particle size of bed material on the tracer distribution are investigated. A quantitative comparison of lateral dispersion coefficient shows that our results agree fairly well with measurements and predictions of correlations for lab‐scale fluidized systems in previous studies. The presented 2D profiles of the lateral mixing can be used to validate fundamental solids mixing models or verifying convenient measurement techniques. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

气-固微型流化床压降特性及最小流化速度的实验研究

在内径3～20 mm的4个气-固微型流化床中,分别考察了A类和B类两种类型颗粒的流化特性,同时研究了床几何结构、操作条件、物相性质等各因素对其最小流化速度的影响.结果 表明,气-固微型流化床中的床层压降特性与颗粒类型密切相关,不同的流动状态下两种类型颗粒的流动特性存在显著地差异.在固定床阶段,与B类颗粒相比,A类颗粒与...     

Stability analysis of perforated plate type single stage suspension fluidized bed without downcomer

The stability of operation of a perforated plate type suspension bed without downcomer was analyzed experimentally and numerically. The effects of the feed rate, the gas flowrate and the opening ratio and hole diameter of the perforated plates on the operating stability of the fluidized bed were examined. A full three-dimensional discrete particle simulation method proposed by Tsuji [1993] was performed to study the formation of a stable suspension fluidized bed. The course and behavior of particles that formed a dense and stable fluidized bed are discussed. Both the experimental and simulation results of this study show that the process of forming a suspension bed can be categorized into (i) an induced stage, (ii) a growing stage, and (iii) a stable stage. The velocity of gas through the orifice directly controls the formation of the bed while the solid flow rate over a considerable range maintains a balanced hold-up in the suspension bed system without downcomers. The existence of a multiplicity of steady states corresponding to different gas flow rates, for the same feed rate and perforated plate type, was observed. Results show that the design of the plate, the particle feed rate and the gas velocity distribution through the hole affect the stability of the fluidized bed. The simulated results agree qualitatively well with experimental observations.     

纳米二氧化硅的流态化行为及卧式流化床多釜串联模型

采用大型立式流化床,考察了气相法制备的纳米SiO2颗粒的流态化行为,研究了不同进料量下床层压降与气速的关系,得到了纳米SiO2体系的膨胀和塌落曲线. 利用多釜串联模型,研究了卧式流化床内挡板数目、物料流量等因素对纳米SiO2的停留时间分布密度和分布方差的影响. 结果表明,等间距设置2块挡板时,物料流动已明显偏向平推流,多釜串联模型参数N接近4. 在实验研究的基础上,设计了大型卧式流化床结构参数,脱酸后产品SiO2颗粒的pH值可达4.0以上,能满足工业生产需要.     

流态化气相沉积中FeSi5Cr5.5/SiO2核壳结构的演化过程

以正硅酸乙酯为SiO2绝缘介质前驱体,FeSi5Cr5.5合金球形粉末为基体,研究了流态化气相沉积中FeSi5Cr5.5/SiO2核壳结构的形成时间及演化过程。利用X射线衍射仪、场发射扫描电镜和X射线光电子能谱仪对不同沉积时间下制备粉末样品的显微特征进行了分析,利用振动样品磁强计和四探针电阻率测试仪表征了粉末样品在室温下的磁滞回线和电阻率。结果表明,在流态化气相沉积过程中,从原料FeSi5Cr5.5合金粉末到完全转换成FeSi5Cr5.5/SiO2核壳结构粉末至少需要30 min,且转换过程符合三维岛状形核生长模型。在FeSi5Cr5.5/SiO2核壳结构中分别存在5种氧元素结构和4种硅元素结构,形成FeSi5Cr5.5/SiO2核壳结构后粉末电阻率提高了3~4个数量级,但饱和磁感应强度降低了约9.6%。     

A new model for ejected particle velocity from erupting bubbles in 2-D fluidized beds

A new model is proposed for obtaining the velocity profile of the particle ejected from the bubble dome in a freely bubbling 2-D fluidized bed. Its basis is the supposition that the initial velocity of the ejected particles, with a direction perpendicular to the dome contour, depends on bubble velocity and bubble growth velocity. This model differs from those previously appearing in the literature in that it is valid not only for vertical-ascent circular bubbles.Experiments were carried out in a freely bubbling 2-D fluidized bed using a high-speed video camera to measure the velocity profile. Upon comparing these results with the proposed model, it was established that, excepting some isolated cases, the model properly predicts the magnitude and direction of the maximum particle ejection velocity and the velocity profile.Using the work of Shen et al. (2004. Digital image analysis of hydrodynamics two-dimensional bubbling fluidized beds. Chemical Engineering Science 59, 2607-2617), we obtain two general equations for the bubble velocity and the bubble growth velocity in a 2-D fluidized bed. These expressions, together with the proposed model, can be used to calculate the initial velocity of the ejected particles.     

Factors Affecting Stable Operation of Counter‐current Multistage Fluidized Bed of Solid‐liquid System — Dimensions of Downspout

For the effective use of an ion exchange resin, a counter‐current multistage fluidized bed has been developed. An appropriate design of the downspout, which works to let particles flow down to next stage, is essential to obtain a stable resin flow. From an experimental study on the particle holdup and pressure drop in the multistage fluidized bed, a method to determine the downspout size has been developed. The relation between the liquid velocity within the downspout and the superficial liquid velocity has been derived from considering the pressure balance between the part of the fluidized bed and that of the downspout.