Mechanical Packing of Spherical Particles

An idealized experimental study of particle packing was made. Spherical metal shot of several discrete, narrow size ranges was efficiently packed in glass containers by mechanical vibration. Packing arrangements and the dynamic process of packing were studied visually. One-size spheres packed in an orthorhombic arrangement with a density 62.5% of theoretical density. Forming of high-density multicomponent packings was shown to require at least a sevenfold difference between sphere sizes of the individual components. A quaternary packing with a density 95.1% of theoretical density was formed from spheres with diameter ratios 1:7:38:316 and volume compositions 6.1:10.2:23.0:60.7%, respectively. Such packings could be poured from their glass containers, thus proving that effective mechanical packing is simply an efficient arrangement of spheres of prescribed sizes and proportions. The significance and utility of this work to the ceramic and other industries is discussed.     

柱型水力旋流器柱段长度的研究

针对柱型水力旋流器,以能量损失最小和最佳分离效率为目标函数,运用Fluent软件进行数值模拟,获得旋流器柱段的最佳长度以及柱段长度和溢流管插入深度的最优关系。     

Studies of the Effects of Particle Size Distribution on the Packing Efficiency of Particles

In the studies of pigment volume effects in paint films, particle packing has been shown to be very important. The effects of particle size distribution on this packing has been known but has received little quantitative consideration. In this paper we consider the packing of real and model continuous distributions of particle sizes. An extension of an algorithm for the calculation of random densest packing is given which applies to continuous distributions. Using a log-normal distribution as a model, the effect of the width of a single distribution on packing is considered. Mixtures of distributions are also considered with the calculation of packing efficiency as a function of mean size ratio and distribution widths. Maxima are shown to occur in the packing efficiency of mixtures of distributions as a function of the volume fractions of the individual distributions. The implications of these packing variations in real systems are then discussed.     

流体床内细长颗粒的浓度分布(英文)

In this study, a three-dimensional model based on RANS, slender-body theory and Newton-Euler dynamics is established to study the number concentration, one of the most important fluidization characteristics of cylindrical particles. Also, the effects of interaction between cylindrical particles are taken into account by introducing the rigid collision dynamics. To validate the model, the fluidization experiments of cylindrical particles in a cold-state fluidized bed are carried out. The number concentration characteristics of cylindrical particles are obtained from computational fluid dynamics (CFD) simulation. It is found that cylindrical particles arriving at the exit of the riser the earliest come from the near-wall regions, the horizontal transfer of so many cylindrical particles from the radial centre regions to the near-wall regions is evident. Meanwhile, there is no distinct relationship between the number concentration and inlet wind velocity.     

Packing of Quaternary Mixtures of Fibrous Particles

This paper presents an experimental investigation of packing of quaternary mixtures of fibrous particles of the same diameter but different lengths. The results indicate that the packing density is heavily dependent on the fractional solid volumes and hence the size and shape distributions involved. The packing of fibrous particles appears to be dominated by the shape effect rather than the size effect, and can be satisfactorily predicted by the modified linear packing model.     

Packing of Ternary Mixtures of Nonspherical Particles

An experimental investigation of the packing of some ternary mixtures of nonspherical particles has been conducted. The double extrapolation method is used to determine the packing density of a particle mixture in infinite space. The application of experimental design to particulate mixture problems is demonstrated. The results indicate that the similarity between the packing systems of spherical and nonspherical particles can be readily depicted in terms of specific volume variation.     

双峰分布颗粒的凝并

利用离散分区模型,对初始分布为双峰分布的气溶胶颗粒的凝并情况进行了数值计算.讨论了权重系数、双峰的几何标准偏差以及双峰间距等对无量纲化时间τc(颗粒通过凝并达到"自保持"分布所需要的时间)的影响情况.计算发现,对于不同的初始分布,其达到"自保持"分布所需的无量纲化时间τc不同.当双峰间距增加时,无量纲化时间τc也随着增加.     

宽筛分硅粉颗粒的流化特性

Fluidization characteristics of silicon particle system are studied by the pressure fluctuation method.The existence of fine particles in the system can improve fluidization. Silicon particles with a wide size distribution,preferably with some fines, behave as Group A particles according to Geldart classification, although the system belongs to Group B actually. The system is also approved to be suitable for organochlorosilane monomer production using a fluidized bed reactor. Experimental data obtained in this work are important for the design and operation of commercial fluidized bed reactors for the production of organochlorosilane monomers.     

Fluidization Characteristics of Silicon Particles with a Wide Size Distribution

Fluidization characteristics of silicon particle system are studied by the pressure fluctuation method. The existence of fine particles in the system can improve fluidization. Silicon particles with a wide size distribution, preferably with some fines, behave as Group A particles according to Geldart classification, although the system belongs to Group B actually. The system is also approved to be suitable for organochlorosilane monomer production using a fluidized bed reactor. Experimental data obtained in this work are important for the design and operation of commercial fluidized bed reactors for the production of organochlorosilane monomers.     

CFD-DEM Simulation of Superquadric Cylindrical Particles in a Spouted Bed and a Rotor Granulator

The fluidization behavior of cylindrical particles in a spouted bed was first investigated experimentally using a camera setup. The obtained average spouted bed height was used to evaluate the accuracy of different drag models in CFD-DEM simulations with the superquadric approach to model the particle shape. The drag model according to Sanjeevi et al. showed the best agreement. With this model, cylindrical particles were simulated in a rotor granulator and the particle dynamics were compared with the fluidization of volume equivalent spherical particles.     

活性组分非均匀分布催化剂颗粒性能研究的进展

活性组分非均匀分布催化剂颗粒,与均匀分布者相比,常可给出较高的活性、选择性和抗毒稳定性.截止到1986年有关这一领域的理论和实验研究文献,Doughety和Verykios已作了极好的综合评述,但除Juang和Weng外,未能论及我国其它学者的工作.本文主要对有关非均匀活性分布催化剂颗粒内部行为的文献进行综述,内容包括等温、非等温条件下单一和复杂反应网络的理论模型、实验研究,以及重点放在解析法方面的活性分布最优化.从文献的来源讲,也述评了我国学术界的工作以及直到1989年在这一领域的最新成果.文章试图对文献中见到的点速率常数和活性分布表达式加以整理,并给出一种适用于任意单一或复杂反应网络的通用理论模型方程.对Thiele模数的形式也作了一般化.     

水泥粉体颗粒的新型PH堆积模型的研究

已有的水泥粉体颗粒堆积模型有一些不足,不能完全满足水泥粉体颗粒这一特定的体系,为了实现水泥的高效应用,本文借助等径球理论在Horsfied堆积模型基础之上提出一种新的PH堆积模型.满足该模型粒度分布要求的粉体颗粒具有较高的堆积密度和较少的细颗粒含量,同时增加了3～ 32 μm部分颗粒,应用于水泥粉体颗粒体系后,水泥水化样具有较高的抗压强度和较低的孔隙率.     

Packing Structure of Particles in a Green Compact and Its Influence on Sintering Deformation

The anisotropy of the structure in a die-pressed compact was studied directly through detailed analysis by confocal scanning laser fluorescent micrographs. The use of confocal optics and an immersion liquid produced micrographs that represented the structure of a cross section at a certain depth along two directions: parallel and normal to the pressing direction. The network formed by particles in contact was analyzed by measuring the components of particle contact parallel and normal to the pressing direction in the green compact. Different values were obtained in the total components of particle contact for the horizontal and normal directions for the cross section parallel to the direction of pressing: the ratio between these values was 1.15. This suggests that there should be 15% more shrinkage in the direction parallel to pressing, at least during the initial stages of sintering when the particle geometry is preserved.     

提升管反应器中颗粒浓度径向分布的力学特性

采用空气动力学中的Kutta-Joukowski升力定理分析了提升管内颗粒的受力,得到了Kutta-Joukowski力FK-J的计算公式FK-J=ρg(vg,Z-vp,Z)(?vp,Z/?r)r.根据在大型冷模实验装置上由PV-6D型颗粒密度两用仪测量的局部固含率和颗粒速度径向分布的实验数据,计算了Kutta-Joukowski力在提升管内的分布特征,分析了颗粒循环量、表观气速、轴向位置对其径向分布的影响.结果表明,当无因次半径r/R=0时,FK-J=0,在r/R=0.85时,FK-J最大;FK-J随颗粒循环量增大而增大,表观气速对FK-J的径向分布没有显著影响;在提升管内的充分发展段FK-J的数值明显大于提升管加速区和出口约束区.由实验数据回归出了提升管内FK-J径向分布的经验关联式,计算值与理论值吻合较好.     

Charge Distribution of Incipient Flame-Generated Particles

We report the size and electrical charge distributions of incipient nanoparticles generated in atmospheric pressure hydrocarbon/air premixed flames in conditions prior to the onset of soot particles. The particle size and charge distributions are measured by Differential Mobility Analysis (DMA) and compared to theoretical charge distributions predicted for flame conditions. The results show that the charge distribution attained in flames is well predicted by Boltzmann theory for all particles, including even the smallest incipient particles with diameters in the 1–3 nm size range. In flame conditions that produce only particles smaller than 3 nm, the charge fraction of particles agrees with that predicted by Boltzmann theory near the flame temperature (1700 K). In flame conditions with ‘bimodal’ particle size distributions, the charge fraction of the smallest particles agrees with the Boltzmann prediction at maximum flame temperature, while the charge fractions of larger particles agree with Boltzmann theory at temperatures that coincide with the local temperature near the probe surface (1000–1200 K). The results of this paper show that the temperature of the Boltzmann charge fraction that best agrees with the measured charge fraction for each particle size gives the local temperature of their last coagulation event. The smaller particles, which retain their charge fraction predicted by Boltzmann at the maximum flame temperature, do not thermalize by coagulation in the cool region near the probe evidencing low probability for charge transfer as well as for coagulation.     

Diffusive Capture of Magnetic Particles by an Assemblage of Random Cylindrical Collectors

Abstract

We develop an effective medium model describing the capture of ultra-fine magnetic particles (diameter much less than 1 µm) by an assemblage of parallel magnetic cylinders, randomly distributed in static fluid. The continuity equation describing the dynamics of concentration is solved numerically to obtain the concentration in various regions around the collector. The concentration contours are generated and the saturation, accumulation, and depletion regions are indicated. The effect of varying collector packing fractions appears significantly in regions close to the outer boundary of the representative cell where the build-up features of ultra-fine particles near the collector surface are similar for packing fractions in range 5–10%.     

内置螺旋挡板流化床颗粒停留时间分布

采用脉冲示踪法在内置螺旋挡板冷态鼓泡流化床上研究了螺旋挡板、加料速率、流化风速、颗粒粒径和床料高度对颗粒在流化床内停留时间分布的影响. 结果表明,颗粒停留时间的无量纲方差从无螺旋挡板时的0.558减小到有螺旋挡板时的0.085,螺旋挡板可有效抑制颗粒返混,增大颗粒运动的平推流趋势;加料速率增大为约2倍时,停留时间减小为约50%,流动更趋向于平推流;床料高度增加,颗粒返混加剧,颗粒平均停留时间及无量纲方差均增大,颗粒运动向全混流靠近;随流化风速增大,颗粒平均停留时间变长;实验范围内,颗粒粒径对颗粒停留时间分布影响不大.     

Temperature Distribution in Fluidized Beds of Porous Particles with Liquid Injection

Liquid injection in fluidized beds is used to add reactants or to improve the heat management in the reactor. This injection will increase the complexity of reactor due to the formation of agglomerates. In this work the effect of the injection on the particle temperature distribution in a fluidized bed of porous particles is determined experimentally using particle image velocimetry and infra-red thermography. The main property of the porous particles influencing the distribution is the specific surface area. In addition, the porosity has a large effect on the defluidization of the fluidized bed.     

Effect of Agglomerate Size Distribution on Loose Packing Fraction

Discrete element modeling was used to establish the effects of size distribution on loose packing fraction during the fall of 5000 to 10 000 agglomerates. Monosized distributions exhibited slightly lower packing fraction than narrow distributions. However, broad distributions always produced the lowest packing fraction. The application of radius ratio rules had an effect opposite to that intended. Smaller fines had a disproportionately large effect on packing fraction, an effect attributed to gaslike behavior. Gravity-driven random packing in ceramic agglomerates was governed by a combination of bridge formation and kinetic agglomerate–agglomerate interactions, not by geometric constraints.     

连续进出料鼓泡流化床颗粒停留时间分布

针对双流化床气化或双床热解气化工艺中鼓泡床反应器的设计,采用脉冲法研究了Geldart B类固体颗粒在连续颗粒进料和出料的矩形流化床内的停留时间分布(RTD),考察了气速、床料高度、粒径、物料流率等操作参数对RTD的影响. 结果表明,物料流率、床料高度、粒径是影响颗粒RTD的主要因素,而气速则是次要因素. 随物料流率和粒径增加,鼓泡床内颗粒流动向平推流靠近;随床料高度增加,物料在床内的混合更加充分,颗粒流动向全混流靠近. 根据实验结果,推荐采用比理想平推流时间低9%~18%计算平均颗粒停留时间.