大颗粒作用下微细粉流态化干燥研究

为了克服湿微细粉易于结团形成“细粉群”、不易流化和干燥的缺点，在微细粉中加入惰性大颗粒物料，由于大颗粒的“搅动”作用，使细粉分散，可提高流化质量，从而提高微细粉的流化干燥热效率．在实验基础上进行了物料衡算和热量衡算，并进行连续干燥热效率的计算．该方法为微细粉的流化干燥提供一条新的途径．     

污泥颗粒与河砂混合流化特性的实验研究

在内径f105 mm、高800 mm的冷态流化床实验装置上进行了污泥颗粒与河砂混合流化特性的实验研究,获得了污泥颗粒水分、污泥颗粒与河砂的质量比对混合物料的流化特性的影响规律. 实验结果表明,污泥颗粒的水分、污泥颗粒与河砂的质量比会影响混合物料的最小流化速度,也影响污泥颗粒与河砂混合的均匀程度. 污泥颗粒的质量比越大,混合物料的最小流化速度越大;污泥颗粒的水分含量越高,混合物料的最小流化速度也越大;污泥颗粒与河砂的质量比越接近1:1,越容易实现充分混合. 在对实验数据进行分析处理的基础上,提出了污泥颗粒与河砂混合物料的最小流化速度经验方程,为流化床污泥颗粒干燥工艺提供基础数据和设计依据.     

PVC类废塑料在冷态流化床中流化行为的研究

在Φ50 mm×800 mm圆柱体的冷态流化床反应器中,对PVC类废塑料、石英砂及其混合物的流化特性进行了研究。研究了PVC颗粒粒径与混合物料中PVC质量分数对混合物料的流化特性的影响规律,得到指导热态实验的关键参数。实验结果表明,PVC颗粒粒径与混合物料中PVC质量分数会影响混合物料的最小流化速度,也影响PVC颗粒与石英砂混合的均匀度。混合物料中PVC的质量分数越小,其最小流化速度就越小,混合物料也越容易实现充分混合;PVC颗粒为Geldart B类颗粒,但由于形状不规则,黏性力大,塌落特性明显,流化性能较差,显示出C类颗粒的流化特性,同时实际的最小流化速度要大于理论最小流化速度。PVC与石英砂混合物料冷态流化行为的研究结果为热态流化床降解PVC颗粒提供了基础数据和实践依据。     

粘附性颗粒添加组份流态化实验

以不同粒径的ＳｉＣ为物料,考察了表观气速和添加颗粒对其流化性能的影响．实验表明,平均粒径大于１０μｍ的ＳｉＣ物料,可通过增大表观气速使其流化;而小于５μｍ的ＳｉＣ５和ＳｉＣ２物料,不能使用增大表观气速的方法使其流化．添加颗粒能使ＳｉＣ５很好流化,利用流态化聚团准数Ａｅｆ可计算颗粒的最佳添加量ｘｍ．     

生物质焦与煤焦混合物的共流化实验研究

生物质与煤流化床共气化,其混合物料的流化实际上是两者焦的共流化,对其共流化行为特性的研究是共气化工艺过程的基础.实验考察了三种粒径的煤焦分别与两种粒径的玉米芯焦和甘蔗渣焦在不同混合比例下的共流化特性.结果表明,煤焦的加入可以明显改善生物质焦的流化效果,煤焦与生物质焦粒径和密度的差异以及表观气速均影响着混合物的混合分离程度.在实验中,对煤焦与玉米芯焦的混合物,煤焦的粒径普遍小于玉米芯焦的粒径,混合物的最小流化速度随煤焦的质量分数增大而减小,反之,呈现分离状态的物料,其最小流化速度随煤焦的质量分数增加而增加.     

碳纤维复合材料回收装置中物料停留时间研究

为保证所回收的碳纤维能及时有效地被排出,用EPE泡沫为示踪物料,在建立热氧裂解法回收碳纤维的装置上,用实验法测定了卧式流化床反应器的流化曲线。经分析流化曲线得出临界流化速度和带出速度并经公式计算确定了临界流化速度和带出速度,考察不同形状物料及混合物料在主反应器内的停留时间。结果表明,流化床内临界流化速度为0.15m/s,颗粒带出速度为0.24m/s;物料形状对其在床内停留时间影响较大;单一形状物料在流化床内停留时间由长到短依次为圆柱体、长方体和球体;球体物料最易排出;混合物料在床内停留时间由长到短依次为球体与圆柱体混合物料、长方体与球体混合物料和长方体与圆柱体混合物料;长方体与圆柱体混合物易排出;为使回收碳纤维尽快排出流化床,可采用长方体和圆柱体混合物料或单一的球形物料进行热试验研究。     

超细粉在导向管喷动床中的流化行为

以料径5μm的CaCO3超细粉为物料，对其在半圆形导向管喷动床中的流化行为进行研究，考察床层压降特性及喷嘴直径、导喷距及导向管直径对起始流化行为的影响。     

离心流化床初始流化状态的研究(Ⅱ)实验研究

对离心流化床初始流化状态进行了实验研究。结果表明,下行程床层压降流速曲线的规律一致,流化时床层压降趋于稳定;上行程曲线受床体结构、物料装填方式和运行状况的影响很大。实验测定初始流化速度应采用下行程曲线。可视性实验证实了离心流化床逐层初始流化,已流化部分的床层物料充分混合。     

纳米TiO2颗粒在声场流化床中的流化特性

以原生纳米级TiO2颗粒为物料，在内径为130mm的声场流化床中，考察声压、频率对纳米颗粒的流化特性的影响。结果表明，适当的低频强声波的引入能很好的抑制沟流，消除节涌，大大降低了流化床中纳米颗粒聚团的尺寸，使之在低气速下实现稳定流化，从而显著改善纳米颗粒的流化质量。     

单组分颗粒振动流化床的流体力学研究（1）——起始流化时床层压降

国内外振动流化床流体力学的研究由于实验条件的限制，其结果尚存在着分歧，在此情况下，本文在内径为１４８ｍｍ的振动流化床下，研究Ｇｅｌｄａｒ‘ｓＡ，Ｂ，Ｃ类物料起始流化时的床层压降，分别研究了颗粒物性与振动特性对床压降的影响，并且根据上述因素的影响，关联了起始流化时床层压降的计算式，并与画外学者的关联式进行了比较。     

细颗粒的团聚流态化及其判定

本文在考查了不同细颗粒的流态化过程及物料的气动特性与粘附力关系的基础上，提出了当量流态化的概念；实验发现聚团密度的减小是改善细颗粒流化性能的一种有效途径；根据气动情况下不同的成团结果，把细颗粒的聚团流态化分成了三类：沟流；似A类聚团流态化；似B／D类聚团流态化；同时，结合实验结果，给出了不同细颗粒聚团流态化类型的定量判据     

EFFECT OF VARIABLE ACOUSTIC FIELD AND FREQUENCY ON GAS-SOLID SUSPENSION OF FINE POWDER: A REVIEW

Suspensions of fine particles in either Newtonian or non-Newtonian fluids are often encountered in the physical, engineering, and biological sciences. For example, the manufacture of particle-laden products such as reinforced composites, paints, paper, slurries, and cements involves the processing of particle suspensions. Fine particles become difficult to suspend due to interparticle attraction forces like ver der Waals, capillary, and cohesive forces, which are responsible for converting fine particles into aggregates. These aggregates prevent the particles from being suspended uniformly, hence external forces are essential to break these aggregates. External forces include magnetic fields, electrical fields, acoustic fields, and mechanical vibration, which are useful to break aggregates and suspend particle uniformly. This process is termed homogeneous fluidization. This article presents a comprehensive review of sound-assisted fluidized beds for group C, A, and B and binary materials. Furthermore, this review covers the effect of acoustic field intensity and frequency on minimum fluidization velocity and on bubbling.     

C类物料磁场流态化(Ⅰ)──机理研究

本文系统地研究了磁场改善C类物料流化质量的机理，并在此基础上推导出气泡大小与磁场强度等操作条件之间的数学模型；本研究还对铁磁性物质在流化床内发生凝聚的现象进行了分析，得到能预报铁磁性物质发生凝聚的无因次数．     

FLUIDIZATION UNDER EXTERNAL FORCES (Ⅰ) MAGNETIZED FLUIDIZATION

Fluidization under the action of external forces has recently received much attention at home and abroad.Funda-mental study in this novel field has led to the creation of new techniques and equipment in chemical and biochemical pro-cesses,such as reactors for catalytic and pseudo liquid-solid reactions as well as contaetors for gas-liquid-solid systems.In conventional fluidization,solid particles acquire fluidity under the action of a gas or liquid passing at a sufficientvelocity.Under the action of external forces,fluidization can take place at fluid velocities higher than that for particleelutriation or lower than that for incipient fluidization under normal conditions.These external forces can often help toavoid bubbling or suppress backmixing,thus improving mass and heat transfer.Studies on fluidization under various ex-ternal force fields,such as magnetic,oscillating,centrifugal,and ultrasonic,will be reported in a series of papers.     

粘性SiC颗粒聚团流态化特性

对不同粒径的°SiC粘性颗粒的流态化实验表明,颗粒粒径对流化性能有较大影响,颗粒粒径越小,颗粒间粘附力越大,其流化性能越差;提出了粘性颗粒自然聚团数Ae_n和流态化聚团数Ae_f,用来表征颗粒的流化性能;指出了应开展粘性颗粒聚团流态化的研究。     

Improvement of the Fluidizability of Cohesive Powders through Mixing with Small Proportions of Group A Particles

The gas fluidization behaviour of fine cohesive powders, classified as Geldart group C, is known to be characterized by cracks and channels leading to severe non‐homogeneities in the bed. Geldart group A particles, on the other hand, are known to show more homogeneous and regular fluidization behaviour. This paper studies the effects of the addition of small proportions of group A on the fluidization behaviour of a group C powder. Differential pressure fluctuations data at a sampling frequency of 200 Hz were recorded for two cases. In the first case, the bed contained only group C powder while in the second case small amounts of group A particles were added to the existing group C powder. Visual/image observations coupled with time series analysis showed that the addition of small proportions of group A particles substantially improved the fluidization behaviour of the bed even at low superficial gas velocities, leading to a more uniform fluidization. Evaluation of mean and standard deviations has shown the advantage of mixing the two powders as it allowed larger pressure fluctuations and smaller standard deviations. Power spectra, on the other hand, showed that unlike group C, for which fluctuations were small in magnitude and broadband in structure, the mixture showed stronger periodic behaviour as result of the attenuation of the small and rapid fluctuations caused by the flow of gas in the cracks and channels. Advanced methods such as the principal component analysis of the embedded trajectories allowed a quantitative comparison between the fluidization behaviour of the two systems.     

Interpretation of Geldart's type A,B, C and D powders by taking into account interparticle cohesion forces

By taking into account interparticle cohesion forces, one can derive limiting conditions which result in a classification of powders which is equivalent to the definition given by Geldart [1].Separation of powder type A from powder type C follows from the condition that free particle motion is suppressed by the dominance of cohesion forces in the case of powder type C.Separation of powder group B from powder group A is defined by the unimportance of cohesion forces on fluidization behavior in the case of powders of type B.Separation of powder group D from powder group B is defined by the fact that for minimum fluidization of powders of type D the dynamic pressure of the fluidizing agent exceeds a distinct value depending on particle size and density difference.     

A numerical study of fluidization behavior of Geldart A particles using a discrete particle model

This paper reports on a numerical study of fluidization behavior of Geldart A particles by use of a 2D soft-sphere discrete particle model (DPM). Some typical features, including the homogeneous expansion, gross particle circulation in the absence of bubbles, and fast bubbles, can be clearly displayed if the interparticle van der Waals forces are relatively weak. An anisotropy of the velocity fluctuation of particles is found in both the homogeneous fluidization regime and the bubbling regime. The homogeneous fluidization is shown to represent a transition phase resulting from the competition of three kinds of basic interactions: the fluid-particle interaction, the particle-particle collisions (and particle-wall collisions) and the interparticle van der Waals forces. In the bubbling regime, however, the effect of the interparticle van der Waals forces vanishes and the fluid-particle interaction becomes the dominant factor determining the fluidization behavior of Geldart A particles. This is also evidenced by the comparisons of the particulate pressure with other theoretical and experimental results.     

Onset of an innovative gasless fluidized bed—comparative study on the fluidization of fine powders in a rotating drum and a traditional fluidized bed

Geldart group C powders were found to be fluidized in rotating drums without requiring any external fluidizing gas. As a result, a rotating drum was proposed as a new gasless fluidized bed in contrast to a traditional fluidized bed, leading to a considerable amount of energy savings. In addition, the fluidization qualities of a series of Geldart group C powders were found to be further improved with the assistance of drum rotation because of the shearing movement among particles that eliminates channeling and cracks and possibly also breaks agglomerates. There is potential for the new gasless fluidized bed to replace some traditional fluidized beds where the fluidizing gas is not used as a reactant.In the gasless fluidized bed, a boundary layer of compacted powder adjacent to the drum wall was observed. The powder in this layer is carried up to the freeboard and then falls back to the powder bed, forming a powder circulation in the drum. The circulating powder leads to a circulation of internal gas in the drum, which essentially acts as fluidizing gas to realize the fluidization of Geldart C powders in the drum. In contrast to the fluidization of Geldart C powders, Geldart groups B and D powders show cascading and cataracting motions instead in the rotating drum due to their requirement of higher fluidization gas velocities. Geldart group A powders experience a transition of powder behavior between Geldart group B–D powders and C powders.     

Fluidization characteristics of fine particles

A new voidage function is defined based on the Blake–Kozeny equation. This voidage function gives better correlations than those heretofore used in describing minimum fluidization characteristics. Due to the inter-particle cohesive forces, the channelling and bubbling often exist in the fluidization of fine particles. In consideration of the channelling effect, a correlation of the fluidization friction factor is proposed. It is also shown in experiments that the channelling in fine particle systems is reduced when coarser particles are added.