FLUIDIZED BED PRESSURE DROP IN PROMOTED GAS-SOLID BEDS WITH COAXIAL ROD, DISK, AND BLADE TYPE PROMOTERS

Bed pressure drop equations have been formulated for gas-solid fluidized beds with different types of promoters using Ergun's equation (Ergun, 1952) and experimental data. Four rod promoters, seven disk promoters, along with one blade promoter were used in beds supported on five different distributors with open areas of 12.9%, 8.96%, 5.74%, 3.23%, and 1.43% of the column section. The predicted values of bed pressure drop using a modified (i.e., modified numerical constant) Burke-Plummer (Burke and Plummer, 1928) equation were compared with the corresponding experimental as well as the respective values obtained with the help of Kumar et al. (submitted) and traditional gas-solid fluidized bed equations.     

快速流化床压降之研究

本文介绍了在两个不同床径的快速流化床上,用5种固体物料所进行的床层轴向压降的实验工作。并用以前所进行的φ115快速床的压降关联式为基础,对三个不同床径的压降数据进行了多元拟线性回归,得出了一个比较好地预测压降值的经验关联式。式中包括气速、固体循环量、颗粒带出速度、固、气密度比和快速床的床径等参数。预测值和实验值的平均误差为15.7%,个别点大于±20%。     

MASS AND MOMENTUM TRANSFER WITH NON-NEWTONIAN FLUIDS IN FLUIDIZED BEDS

A new model for non-Newtonian fluid flows through fluidized beds is developed by extending the Richardson-Zaki concept. In the proposed model, the existing correlations for an isolated single sphere are simply extended to those for a fluidized bed by incorporating a voidage function. The model is found to be in a good agreement with other correlations for flows of a non-Newtonian fluid through multi-particle systems. The model is also applied to interpret mass transfer in fluidized beds.     

MASS AND MOMENTUM TRANSFER WITH NON-NEWTONIAN FLUIDS IN FLUIDIZED BEDS

A new model for non-Newtonian fluid flows through fluidized beds is developed by extending the Richardson-Zaki concept. In the proposed model, the existing correlations for an isolated single sphere are simply extended to those for a fluidized bed by incorporating a voidage function. The model is found to be in a good agreement with other correlations for flows of a non-Newtonian fluid through multi-particle systems. The model is also applied to interpret mass transfer in fluidized beds.     

CHARACTERIZATION OF AXIAL NONUNIFORMITY IN FLUIDIZED BED BY THE AMPLITUDE OF LOCAL PRESSURE DROP FLUCTUATIONS

The amplitude of local pressure drop fluctuations was used to characterize the axial stability of a freely bubbling fluidized bed. The experiments were carried out in a bed of 0.318 m dia at normal and elevated temperatures. It was found that the transition between a freely bubbling zone, consisting of small bubbles distributed uniformly across the bed, and a zone of incipient slugging occurs if bubble to bed diameter ratio is about 0.15. The amplitude of local pressure drop fluctuations was found to be a linear function of gas velocity in a broad range of temperatures if measured in the freely bubbling zone     

MODELING OF THE PRESSURE DROP AND FLOW FIELD IN A ROTATING FLUIDIZED BED

Rotating fluidized beds (RFB) have found applications as dust filters, dryers, particle coaters, and granulators, and recently as catalytic reactors for the clean up of diesel exhaust. However, successful design and operation of an RFB requires an in-depth understanding of the fundamentals of the fluid dynamics involved. In this study, mechanistic models have been developed to account for the pressure drop relationship with respect to rotating speed, flow rate, properties of the granular particles, and fluidization conditions in the RFB. The models show that the total pressure drop across the bed is quadratically dependent on the rotating speed as well as the flow rate. These quadratic relationships have also been validated experimentally. The pressure drop relationship has further been validated through a full flow field numerical simulation of flow through a rotating bed with a slotted cylindrical distributor but without granular particles in the bed. Using our analytical model together with experimental results from three different types of distributors, a slotted cylinder with a thin metal screen, a perforated cylinder with a thin metal screen, and a sintered metal cylinder, three semi-empirical quadratic equations are obtained to predict the pressure drop across these distributors. A comparison of the distributor pressure drop with that across the fluidized bed (granules only) shows that the pressure drop across the distributor is appreciable and cannot be neglected in RFB applications. The higher the rotating speed, the more significant the pressure drop across the distributor.     

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．     

THE EFFECT OF SURFACE ROUGHNESS ON PRESSURE DROP IN A PACKED BED

Particle surface roughness is shown to have a significant effect on the pressure drop in a packed bed of adsorbent particles. The packed bed friction factor is determined using three spherical adsorbents of differing degree of surface roughness in the Reynolds number range 1-62. The results were successfully correlated using a correlation of the Ergun type. It is shown that surface roughness significantly increases the friction factor.     

TRANSITION OF FLOW REGIME IN FLUIDIZED BEDS WITH SLANTING BLADE BAFFLES

A flow model is proposed to investigate the transition of flow regime from bubbling to turbulent fluidization postulating that the flow in the emulsion phase follows the Richardson-Zaki equation.

Void fraction of the whole bed ε_f and the mean velocity of bubbles U_b were measured in fluidized beds of 0.3 and 0.5 m ID, in which slanting blade baffles were positioned. Mo-catalyst, silica gel, sand and glass beads with size between 135-443 μm were fluidized by air.

Void fraction of the emulsion phase ε _e was calculated on the basis of the above model. Correlating ε _e with superficial gas velocity U_ƒ, we found that ε _e was very close to ε _mƒ in the bubbling regime and that e, increased with increasing U_ƒ in the turbulent regime.

Calculated values of the volume fraction of bubble phase δ were correlated with U_ƒ, from which apparent transition point from bubbling to turbulent regime was estimated. Combining information obtained, transition of flow regime in the above type of fluidized beds is discussed     

PRESSURE DROP IN FLOW OF A NEARLY CRITICAL FLUID THROUGH PACKED BEDS OF SPHERES

The flow of nearly critical carbon dioxide through packed beds of glass beads and steel spheres has been investigated. Experiments have been carried out in the intermediate range of sphere Reynolds number. Results show that around the critical point effects of fluid compressibility are negligible, and, therefore, that the friction factor can be expressed as a function of Reynolds number only. Carman [1] and Dolejs and Lecjaks [2] equations show good agreement with the experimental data.     

滴流床式固定化植物细胞反应器中的压降和持液量

滴流床式固定化植物细胞反应器中的压降和持液量袁丽红，周名立，欧阳平凯（南京化工学院应用化学系，南京２１０００９）关键词：滴流床反应器，固定化植物细胞，压降，持液量１前言植物细胞的固定化通常采用海藻胶进行包埋，然后源源不断地提供其营养成分并通入空气，以...     

气固流化床中侧向射流穿透深度的研究

本文以小米和两种硅胶为物料，在314×25mm的二维射流流化床中，用摄像法研究侧向射流穿透深度，并得到了关联式，误差小于25％．当射流倾角变化范围不大、并忽略射流位置的影响时，可以得到简化公式，误差小于40％使用基于对流体模型的计算机程序进行模拟，分析了射流产生的机理，研究了射流气速、直径、倾角和位置对射流穿透深度的影响．模拟值和实验值较吻合．     

高压下滴流床反应器压降和液含率的预测

采用Ａｌ－Ｄａｈｈａｎ的滴流床高压数据，确定了Ｈｏｌｕｂ详细模型中速率滑移因子ｆｖ和剪切滑移因子ｆｓ的关联式，并将简单模型和详细模型的预测与实验结果进行了比较．结果表明：在高压下详细模型的预测效果明显优于简单模型，且与实验值的偏差较小，使得Ｈｏｌｕｂ的基础模型的预测能力大大增强．     

一种气,固流化床料位检测的新方法

料位高度是气、固流化床内重要的基本参数之一。虽然有压降法、测温法、电容法和回波法等可用于料位的测量,但是这些方法作为工业应用都不能令人满意。本文根据流化床内部特性提出了利用流化床内压力波动信号和料面附近的平均压力降测量流化床料位高度的新方法。实验表明,这种方法原理简单,测量精度高。不仅能测量流化床内料位的平均高度。而且还能得到料位的瞬时高度和波动范围;且测量结果不受流化床的几何尺寸、床内物料的特性及流化状态等因素的影响,从而为工业流化床提供了一种料位在线测量的新方法。     

气固流化床压力脉动信号的混沌特征分析

对气固流化床内压力脉动时间序列进行分析,研究了流化床内的混沌特性,分别利用李雅普诺夫指数、相对分散度、分形维数和混沌度来定量描述稳定性、复杂性,自由度和系统状态数,证明四个混沌特征参数的相关性是好的,得到了混沌特性随着气速和床层高度的变化趋势,并且提出气泡行为是流化床内产生混沌运动的重要原因。     

气固流化床中的信息传输

引　言压力脉动信号用于气固两相流检测已经有相当长的时间 ,一般认为压力脉动信号包含了流化床内的许多动态信息 ,是颗粒特性、床的几何特性、气泡运动特性等多种因素的综合反映 .如何有效地从中提取隐含信息也一直是一个广受关注的问题 .在这方面国内外的研究者已经做过不少工作 ,包括早期研究压力脉动信号的均值、方差、功率谱、相关函数等 ,以及后来基于信号的非平稳特性的小波、Ｗｉｇｎｅ -Ｖｉｌｌｅ谱等 ,得到了一些有用的信息 .近年来 ,随着非线性科学的发展 ,有的研究者提出流化床具有显著的混沌特性 ,Ｄａｗ等在 1 990年第 1次发…     

气体的温度和压力及颗粒形状对固定床压降的影响

本文在Ａ－Ｓ方程的基础上推导出气体流经固定床时的压降表达式。     

A SIMPLE METHOD FOR STUDYING THE KINETICS OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR

A methodology for studying the kinetics of gas-solid reactions in a fluidized bed reactor is presented. This procedure is based on the analysis of the response of the system (flue gases) when batches of solids of different weight are added to the reactor. The method has been applied to the study of limestone particle calcination. The calcination rate constants obtained are in good agreement with those found in the literature. The method offers the advantage of simplicity and avoids the use of model assumptions or empirical correlations.     

低、高压滴流床中压降和持液量计算的统一关系式

基于对滴流床中气液两相流动特征尺度的分析,提出以修正的相摩擦系数对相Reynolds数进行关联,获取低、高压滴流床中压降和持液量计算的统一关联式的方法.对于滴流床中单相不饱和流（液体流动,气体静止）情形,以及低压和高压滴流床中两相流、高气液作用情形,收集了文献报道的不同大小颗粒、不同物系的大量实验数据,以相摩擦系数对相Reynolds数进行关联,得到新的压降和持液量计算式,其物理意义明确,计算精度得以提高.     

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。