粉体颗粒流动性的分形维测试法

粉体颗粒粒度分布分形维能很好的表征颗粒群粒度分布.本文通过建立数字显微颗粒粒度分布分形维数值的数学模型,探讨粉体流动参数与颗粒粒度分布分形维数值间的关系,确认颗粒粒度分布分形维数值可以用于表征粉体流动性,形成了可靠和简洁的粉体流动性能测定新方法.     

宽粒度分布的细颗粒沉降

针对浆态床ＦＴ合成中液体蜡与细颗粒催化剂的分离，对与其粒径分布相似的细石英砂与水的体系的沉降分离进行了考察，用超声波浓度仪测定沉降过程中的颗粒浓度。由此得出了沉降过程的浓度场，并从沉降曲线可以看出宽粒度分布的沉降不同于相同或相近粒径的沉降，而且可得出颗粒浓度、悬浮液高度对沉降的影响情况     

NSKC—1型粒度分析仪测定水泥粒度分布及比表面积

粉体粒度的测量方法很多,常见的有筛分析法、Coulter法、激光散射法和沉降法等。目前在水泥工业中比表面的测定采用勃式透气法,而粒度分布的测定一般用筛分析及沉降天平粒度仪。筛分析只适用于粗粒度的测定,70μm以下的颗粒筛分十分困难,因而通常采用沉降天平进行水泥粒度分布的测定。     

沉降终速与颗粒粒度测定

讨论了颗粒体在静止流体中的运动规律；分析了沉降终速在测定颗粒粒径大小及其粒度分布中的应用；介绍了粉末粒度分布测试仪的操作。     

纳米Si3N4陶瓷粉体表面改性的研究

用钛酸酯偶联剂NDZ-102化学包覆纳米Si3N4陶瓷粉体,通过沉降实验、粒度测定和表面能测试等实验手段研究了改性前后粉体的溶液中稳定性、热重、粒度分布等物性.结果表明:NDZ改性纳米Si3N4粉体为化学改性,添加量为10%时,粉体在甲苯中悬浮性最好;粉体改性后粒径降低,为纳米级分布,表面能也大幅度下降.     

试论沉降法测定颗粒粒度及其分布

颗粒的粒度及其分布显著影响粉末的性质和用途，为了掌握生产中产品的质量，必须对粉末进行粒度分布的检测。详细介绍了沉降法的基本原理，实验方法、步骤和结果处理。试验和生产应用表明，粒度测定的方法多种多样，沉降法以其原理简单、易于操作而被广泛采用。     

沉降终速与颗粒粒度测定

讨论了颗粒体在静止流体中的运动规律；分析了沉降终速在测定粒粒径大小及其粒度分布中的应用；介绍了粉末粒度分布测试仪的操作。     

粉体粒度对神府煤制备高性能水煤浆的影响

神府煤内水含量高、氧碳比高,不利于湿法气化制备高性能水煤浆。选择神府同一矿区的原煤、洗煤,通过干磨湿配制浆,并对煤浆性能进行分析。结果表明,煤的可磨指数HGI与磨矿时间共同决定粉体的粒度分布,粉体粒度与煤浆的流动性及稳定性直接相关,磨矿过程应尽可能使粉体粒度偏细。粒度〉0.20 mm的粉体主要影响煤浆的稳定性,较多的大颗粒会因重力沉降作用导致煤浆性能变差;粒度〈0.076 mm的粉体主要影响煤浆的流动性,合适的质量比配能与大颗粒形成双级或多级级配。SFR、SFX制浆性能较好时粒度〈0.076 mm的粉体分别占45%、50%。     

一种分段式宽域粒度沉降分析仪的研制

0引言随着科技的发展,人们开发了多种基于不同工作原理的颗粒粒度的测量方法和测量仪器。最常见的有筛分法、沉降法、Coulter法和激光散射法等。筛分法只适用于粗粒度的测定,70μm以下的筛分就十分困难;Coulter法操作条件苛刻,只适于电解质中悬浮的粉体;激光散射法则有价格昂贵、调整困难、分辨率低和操作复杂等缺点。因而在工业上最常见的是沉降法〖1〗。上世纪80年代以来,我国相继开发了几种光透式沉降粒度分析仪,使我国沉降粒度分析水平得到了长足的发展。配合离心机的沉降粒度分析仪的测量范围通常在0.03～300μm,实际测量中设定的测量…     

粉煤灰粉体颗粒细度与分维数研究

利用分形几何学原理研究粉煤灰粉体颗粒,探讨了粉煤灰粉体粒度的分布特征,测试、计算了相应的分形维数,研究表明：（1）粉煤灰粉体颗粒粒度分布都表现出分形分布,粉体粒度分布的分维值1〈D〈3;（2）粉煤灰粉体颗粒的分维值越大,其细度比和细度模数越小,其形态系数随之增大;（3）粉煤灰粉体颗粒的分维数与需水量比的关系成曲线关系,大致在分维值2以下时,其需水量比逐渐增大;但分维值大于2以后,其需水量比逐渐下降。     

离心沉降法粒度分析──固液分离设备选型依据之一

应用离心沉降粒度分析仪进行粒度分析时，准确、合理地选择沉降介质及圆盘转速等测试条件是获得正确测试结果的关键。粒度分析结果为固液分离设备及分离介质的选型提供了依据。     

Effect of inclination on gas-fluidized beds of fine cohesive powders

Results are presented of an experimental investigation on how bed inclination affects the fluidization and sedimentation behavior of fine cohesive particles. In contrast with the expected Geldart C behavior, and due to self-agglomeration, these fine particles are uniformly fluidized by gas in a vertically oriented bed, displaying a fluid-like regime and expanding smoothly as the gas velocity is increased. When the gas flow supply to the bed is suddenly stopped, the initial sedimentation velocity of the vertically oriented bed is similar to the fluidizing gas velocity as corresponds to uniform fluidization. The main effect of inclination is to induce fluidization heterogeneity. The local gas velocity increases in the adjacent region to the upper wall at the expense of the region adjacent to the lower wall. This situation anticipates the onset of local bubbling in the region adjacent to the upper wall. Meanwhile the region adjacent to the lower wall remains in a solid-like state and does not reach the fluid-like state until values of the gas flow are applied much higher than those needed in a vertical fluidized bed. As a consequence, the expansion and fluidization uniformity of the tilted bed are hindered. If the gas supply to the inclined bed is suddenly stopped, and because of induced heterogeneity, sedimentation takes place at a decreased rate as compared with sedimentation velocity in the uniformly fluidized vertical bed.     

Modeling of sedimentation of polydisperse spherical beads with a broad size distribution

This article deals with experimental and theoretical studies of the sedimentation of polydisperse agarose beads with broad particle size distributions. A light-extinction principle was used to measure the variation of solid concentration in the suspension with time and settling distance. Different experimental conditions have been used to show the influence of solid concentration and liquid density and viscosity on the settling behavior of the beads. The sedimentation process was described mathematically by a system of conservation law using Masliyah's hindered settling function. The physical properties of the beads and the optical properties of the suspension were carefully examined to enable a reliable comparison between experimental and simulation results. The model gives good predictions under all the conditions studied, showing its soundness in formulating the hindered settling process of polydisperse particles in a suspension.     

Formation of Particle Layer Within Coated Slurry Characterized by Thickness Variation

An understanding of the conversion process from slurry to particle layer on a substrate is required for the precise control of the particle alignment and the material distribution in the coated slurry. In this work, variation of coated slurry thickness during drying was applied to evaluate drying and particle layer formation simultaneously. The slurry used consisted of micron-sized silica or poly (methyl methacrylate) particles and an aqueous solution of poly-vinyl alcohol (PVA) possessing differing degrees of hydrolysis. During the drying process, initially the thickness of the coated slurry was observed to decrease at a constant rate in the concentration stage, and subsequently it began to show large fluctuations due to the emergence of particles on the drying surface in the packing stage. In the final fixing stage, the fluctuation of film thickness was restricted because particles were immobilized by highly viscous concentrated PVA or by PVA molecule bridging. Based on the variation and fluctuation of film thickness, we introduced two characteristic dimensionless time ratios: (a) void fraction in a packed particle layer at the end of concentration stage; and (b) the time required to fix particle position after the end of the packing stage. We concluded that the dispersed state and settling velocity of the particle determines the space between particles in a loose packing layer, and we found that the distribution of polymers in a particle layer has a strong influence on the mobility of particles in a tightly packed layer.     

The influence of particle size on the flow of initially fluidised powders

When particles are allowed to move over a horizontal surface, the effect of gas flow through them is to increase the distance over which they move, termed their mobility. This has already been shown for cases when gas is continuously passed through a current of particles, but this investigation shows that this is also true when the gas flow is only initially present. Experiments were conducted on a column of fluidised particles that were released into an enclosed channel by the removal of a wall, and the distance travelled by the particles was measured. The behaviour of fine particles (group A in the Geldart classification of fluidised particles) was distinct from that of larger particles.The mobility was modified when they were mixtures of different-sized particles. In particular, when there was no gas flow, the mobility was a maximum when the proportion of fine particles was 30% and the magnitude of this effect increased with the size of the coarser component of the mixture. All the different mixtures of particles acted in a similar manner with increasing mobility for a given gas flow rate with proportion of fine particles until roughly half the mixture was composed of fine particles, and there was then no further increase.     

沉降法测定十溴联苯醚粒度分布的研究

介绍了用沉降式粒度分布测定仪对十溴联苯醚粒度分布进行测定的条件选择及试验过程。     

Simulation study of production of fine ceramic powders in a cyclone reactor

A numerical simulation study of production of fine ceramic powders in an innovative vapor-phase aerosol reactor is described. Arrangement is typical of reverse-flow cyclone equipment; no similar device is present in current scientific literature and industrial technology. The cyclone reactor has a potential technological application as it realizes process intensification by two simultaneous operating advantages: (i) curly flow reduces recirculation of as-synthesized particles towards flame region, and (ii) cyclone arrangement segregates large particles. As a result, ceramic powders with narrower particle size distribution can be produced with regard to traditional equipment. The study is based on the re-modeling of an existing industrial reactor for production of fine TiO₂ according to a cyclone configuration; particle size distributions from simulation and plant are compared.     

Effect of diffusion and convection on the flux of depositing particles near a preadsorbed particle

A steady state convective-diffusion equation is solved using a collocation method to find the concentration profile and flux of adsorbing particles near a particle adsorbed on a line. At small values of the gravity number, N_G=πd⁴ Δρg/6kT, the concentration profile and flux vary slowly near the preadsorbed particle, while they are highly non-uniform at large values of N_G. The numerical results are compared with Brownian dynamics simulation for a range of N_G values. The effect of the position of the system boundary on the collocation calculation is discussed and it is shown how the concept of flux balance may be used to improve the accuracy of the results. Finally, we develop a truncated power series that accurately fits the numerical data.     

Mechanochemical synthesis and investigations of calcium titanate powders and their acrylic dispersions

In this paper we studied calcium titanate (CaTiO₃) nanopowders obtained via a mechanochemical method assisted by microwave irradiation from calcium oxide and titanium dioxide, as well as its suspensions with addition of acrylic-poly(ethylene glycol) suspensions (SAP) obtained using microwave irradiation as a stabilizing agent. Experiments carried out using X-ray diffraction technique confirmed success of mechanochemical synthesis assisted by microwave irradiation and scanning electron microscopy images allowed to determine the structure as well as dimensions of CaTiO₃ nanopowders. Suspensions of CaTiO₃ and SAP were examined and the results showed relationships between the SAP concentration and both viscosity and stability. Both viscosity and stability are significantly increased upon addition of SAP and the dependency is nearly linear for higher SAP concentrations. Based on the results, we conclude that addition of SAP allows to successfully stabilize CaTiO₃ nanopowders and the stabilizing effect can be explained by both electrostatic and steric forces.     

A new method for the reconstruction of the particle radius distribution function from the sedimentation curve

A new method for the reconstruction of the particle radius distribution function from the sedimentation curve is proposed. This method permits us to obtain a continuous smooth distribution function. Two approaches are compared. The first approach is based on the calculation of the second derivative from the sedimentation curve. The second one is based on the solution of the original integral equation which describes a sedimentation process. Both of these approaches can be reduced to the problem of the solution of the Fredholm integral equation of the first kind. From the theory of integral equations, it is known that this problem is ill-posed. The usual methods lead to unstable solutions and we are forced to use special regularizing algorithms. In this paper, the Tikhonov regularization method is used to stabilize the solution of the integral equation. It is shown that the accuracy of both methods is higher than the accuracy of the graphical method, but the approach based on the solution of the original integral equation gives a more stable solution than that based on the derivative. The accuracy of the new method permits us to reconstruct the fine structure of the particle radius distribution function. Such an analysis cannot be carried out with the rough bar diagram obtained from the graphical method. The new method is absolutely indispensable in technology for controlling the degree of powder fineness.