三相循环流化床中气泡上升速度的实验研究

开发了一种新型的光纤探头多相流气泡测试系统,可用于气－液两相和气－液－固三相体系中气泡参数的测定。应用此系统研究了三相循环流环化床中不同径同位置气泡的上升速度分布,气泡上升速度均值的径向布以及操作条件对这现任中分布的影响。     

液-固流化床中单个变形气泡的上升速度

以气泡在上升运动过程中的受力分析为基础,建立了描述单个变形气泡在液－固流化床中上升速度的理论模。应用该模型分别对球形和球帽形气泡在液－固流化床中的上升速度进行了计算,并将计算民在不同的床内压力,温度与颗粒相体积分数下气泡上升速度的实验测量数据进行了比较。     

用摄影—图像分析法对三相流化床中气泡行为的研究

本文利用35mm 普通摄影机拍摄了300×20×2000mm 的二维床中多气泡的运动行为,并用图像分析仪对摄影胶片进行了分析处理,得到了各个气泡大小、运动速度及所处座标位置。并对大量气泡运动特性进行了统计研究。结果表明采用这一方法能够准确地定量描述流化床中气泡群运动的整体特性,为深入研究、描述气泡的运动规律打下了基础。     

底隙设置挡板内循环流化床水力特性分析

针对流化床反应器中多相流体混合碰撞的复杂性、突变性的问题,以底隙设置十字形挡板反应器的水力特性改变为研究对象,采用电导法测定反应器内液体循环速度和混合时间等动力学数据及其变化,分析新型内构件的强化作用原理。研究结果发现,两相条件下,十字形挡板的设置使反应器的升流区及降流区的液体循环速度分别提高9.5%±1.0%和11.8%±1.0%,低流速时,液相混合时间变长,高流速时,混合时间反而短缩,变化范围在±5%,计算的摩擦阻力系数由4.13降低为2.75,证明了流体在反应器底部碰撞能量消耗的下降。通过全环路能量衡算得到液体循环速度模型计算参数的实验关联式,应用于三相条件,计算值与实验值误差在8%以内。表明在急剧湍流内循环流化床底部设置挡板所实现的流态有序、矢量归一的目标能有效改善反应器中流体的水力特性而使流体稳定,并进一步实现稳态运行条件下的节能。     

多层百页窗式挡板三相流化床中液相混合行为

采用脉冲应答技术测定了矩形气液固三相流化床反应器中液相混合时间和下降速度。考察了挡板结构、气液流量、固体浓度对床层液相混合行为的影响。实验结果表明，在床中设置挡板构件，对液体混合时间与液体下降速度的影响不明显。     

多层百页窗式挡板对三相流化床中液相混合行为的影响

在矩形气液固三相流化床反应器中,采用脉冲应答技术测定了液相混合时间、液体下降速度及液体混合现象。考察了挡板结构对床层液体混合行为的影响。采用多釜串联模型表征液体混合程度。结果表明,在床中设置挡板构件,对床下段液体混合时间、液体下降速度以及液体混合程度的影响不太明显。     

基于图像处理的气固流化床中气泡行为的分析

以数字图像处理为基础,实现对流化床中气泡的成长、聚合和分裂行为的分析.利用高速摄像机拍摄气固两相流的气泡运动图像,从中选取气泡上升、聚舍和分裂三种典型图像序列.经过图像处理后,分别对其进行气泡识别和参数的获取.然后根据获取的数据,首先分析了气泡上升过程中面积、形心、等效直径等参数的变化趋势和变化规律,接着对聚合中的聚合...     

多孔挡板导流筒型流化床内构件研究

筒型内件可以改善气固流化床中气体和固体颗粒的接触，本文对此系统的流体力学特性进行了研究，从而得出数学模型．用此模型模拟鼓泡流化床得到良好结果．     

升温条件下多孔介质内气泡的生长和聚并行为

设计了两种横向和纵向喉道宽度比值(w_h∶w_z)分别为1.48∶1和1∶1的各向异性和各向同性多孔介质微流体芯片,以CO₂为气体,二甲基硅油为液体,采用可视化实验,系统地研究了升温条件下多孔介质结构对气泡生长和聚并规律的影响。结果表明,温度升高引起的传质生长是气泡突破喉道的动力。单个气泡在多孔介质内生长方向的选择依赖于喉道的门阙压力,气泡倾向于突破门阙压力小的喉道。随着温度的升高,气泡侵入和突破喉道速度加快。在各向异性多孔介质中,气泡倾向于在横向生长时与其他气泡发生聚并,而在各向同性多孔介质中,气泡更易发生纵向聚并。当多个气泡存在于各向异性多孔介质内时,气泡的初始分布会显著影响气泡间的生长和聚并过程;在各向同性多孔介质内时,影响则较小。各向异性多孔介质在实际工程应用过程中更易实现气泡流型调控。     

BUBBLE MOTION IN A THREE-PHASE LIQUID FLUIDIZED BED

This paper presents results for the rise velocities of air bubbles in liquids and liquid-solid fluidized beds. The bubble sizes ranged from approximately 0.03 to 0.45 cm radius. Tap water and distilled water were used as the fluidizing liquids. The solid phase consisted of low density alginate gel beads of mean radius 0.04 cm. The gel beads were translucent which permitted observation of bubbles inside the bed even at large solids volume fractions. Experiments were conducted for solids volume fractions ranging from 15% to 52% and in clear liquids. The goal of the experiments was to determine rise velocities of bubbles and to develop and evaluate correlations of bubble rise velocity based on bubble size, solids volume fraction and liquid properties. It was determined that, for moderate solids fractions (ranging from 28% to 45% solids), a semi-empirical correlation that treated the fluidized bed as a pure liquid with a higher viscosity than the liquid phase could be used to represent the data. The Thomas effective viscosity model was used to predict the viscosity. Provided that one restricts attention to a water fluidized bed, a second empirical correlation can be used to represent the data over a broader range of solids fractions.     

INVESTIGATIONS OF THE BUBBLE PHASE BEHAVIOR IN A HIGH TEMPERATURE FLUIDIZED BED REACTOR WITH COALCOMBUSTION

The properties of bubbles in a bench-scale fluidized bed reactor, 30 cm in diameter, during coal combustion were determined by means of a newly developed cooled bubble probe and a data processing system at temperatures up to 850°C and fluidization indexes up to 10 in axial and radial positions in the bed. The fluidization index above 4 and the temperature have only slight effect on the bubble properties. Their variation along the height above the gas distributor is dominant.

Oxygen and Co₂-concentration profiles were measured in the bed and in the freeboard, and the o₂-profiles were calculated by means of measured bubble data and bubble models. A comparison of measured and calculated o₂-profiles indicates that the mass transfer rates between the emulsion and bubble phases are larger than the ones calculated by the models.     

双射流流化床空隙率的分布

在 ３００ ｍｉｎ×５０ ｍｉｎ×２６００ ｍｍ的二维射流床中,采用内径为 １１ ｍｍ的对称双射流管,研究了等速射流条件下射流管间距、喷口射流气速、静床高度对床层空隙率分布的影响,发现射流管间距、喷口射流气速是双射流产生射流区合并的主要原因;并得到了具体实验条件下空隙率分布的数据．同时研究了双射流管不等速射流条件下空隙率分布的规律．     

三相循环流化床中气泡大小及其分布的实验研究

用光纤探头技术对三相循环流化床中的气泡大小及其分布进行了系统研究 ,实验测定了操作条件对气泡大小及其分布的影响规律 .实验结果表明 ,三相循环流化床中气泡的大小分布可用对数正态分布表征 ,在实验条件下气泡平均直径在床中心区域较小且沿半径方向由中心向边壁逐渐增大 ,并随表观气速的增大而减小 ,随固含率的增大而增大 ,表观液速对气泡平均直径的影响较小     

RAINING OF PARTICLES FROM AN EMULSION-GAS INTERFACE IN A FLUIDIZED BED

This paper deals with the raining of particles from an interface between a dense fluidized phase and a gas phase with the fluidized phase uppermost. Such interfaces occur at the upper surfaces of gas bubbles and slugs in fluidized beds. Particle rain in these cases would enhance contact between gas and particles within the bubbles and slugs.

The rise velocities of single square-nosed slugs injected in incipiently fluidized beds of different diameters were measured. Relatively small columns of internal diameters of 0.0125, 0.019 and 0.0254 m were employed in the experiments; In such beds, square-nosed slugs are formed which span the entire cross-section of the beds and rise entirely due to raining of particles from their top surfaces. Since the upper surface of such slugs is flat, their motion can be analyzed using the one-dimensional hydrodynamic theory. Glass ballotini and sand of different sizes were used as bed particles. Comparison of theory and experiment has enabled the determination of the dimensionless gradient diffusivity characterizing the motion of particles induced by a gradient in the void fraction. The results confirm the scaling proposed by Batchelor (1988). The use of the calculated gradient diffusivity in the criterion for stability of a gas fluidized bed predicts the systems under consideration to be always unstable.     

快速流化床内颗粒速度的关联

颗粒速度是快速流化床内重要的流体力学参数,直接测定是困难的,一般都是通过测定其他参数,来计算颗粒的速度。本研究在内径6.6cm 和9.7cm,高3m 的快速流化床内测定颗粒的轴向滞留量分布及压头损失,分析床层内颗粒速度及其影响因素,对三种不同颗粒进行测定,将实验数据进行关联,得出颗粒速度的关联式:适用范围:气体流速:1.4～6.0m/s颗粒循环速度:30～130kg/m~2·s颗粒终端速度:0.133～0.880m/s将实验值与计算的结果比较,基本一致。故可认为该式在实验范围内,可用于推算快速流化床内的颗粒速度。     

FCC细颗粒湍流流化床流体力学性能研究

ＦＣＣ细颗粒湍流流化床流体力学性能研究李俊，张蕴璧，闫遂宁（西安石油学院，西安７１００６１）（西北大学）（洛阳石化公司）关键词：流化床，湍流，气泡，空隙率１前言湍流流化床有着广泛的工业背景。湍流流化床反应器存在着物质空间分布的不均匀现象，这种分布对湍...     

测定气固多孔挡板流化床级间固相返混速率的新方法——光电法

本文提出了测量多孔挡板流化床中级间固相返混速率的光电方法。该方法可用于分别测量通过床中各个挡板的固相返混速率,并可对通过同一挡板不同区域的固相返混速率进行分别测量。本文对该方法的可靠性进行了验证。     

喷液流化床中传热特性

引言流化床反应器由于其特有的众多优点,尤其是传热效果好、床层温度均匀,而在工业上得到广泛的应用．然而随着工业的发展,生产能力的提高,对流化床的换热能力提出了更高的要求．于是出现了许多强化流化床传热的方法,例如乙烯氧氯化反应中的内置换热管法;乙炔制醋酸乙烯中的外加夹套法;催化裂化反应中的粒子循环法．在80年代初期出现了一种流化床带液操作的新方法,它在气相法聚乙烯生产中的应用（其操作工艺被简称为冷凝工艺）具有远大的前景．该工艺是在一般的气相法聚乙烯流化床反应工艺的基础上,在流程中添加易挥发的液体,使反…