不同光学模型对颗粒测量结果的影响

通过试验得出在颗粒粒度测量中，采用Mie散射模型或Fraunhofer衍射模型对检测结果有一定的影响，从理论上对产生差异的原因进行了分析。     

现代颗粒粒度测量技术

颗粒粒度的测定已成为现代测量学的一个重要分支。介绍了筛分法、显微镜法、沉降分析法、电感应法等传统颗粒粒度测量技术的方法和原理 ,并着重介绍了光散射法、质谱法、基于布朗运动的粒度测量法等近年来发展起来的颗粒粒度测量新方法     

图像沉降法测量颗粒粒度的研究

本文提出了图像沉降法，用于快速测量颗粒的粒度分布．该法采用具有2048个元素的图像传感器，沿着沉降高度测量消光强度，消光图像可显示于屏幕上，因而可以观察和监视颗粒的沉降过程．由液体（例如水）表面至任一给定点之间的高度可用图像技术精确地测量，不必借助移动光来或沉降池等附加机械装置．对于粒度为4.5μm的SiC粉末，本法的测量时间仅为5min；为国外同类仪器测量时间的1／5.本文最后给出了一些测量结果．     

颗粒定量测量的计算机图象处理技术研究

采用计算机图象处理、人工智能技术实现了对颗粒的定量分析,阐述了颗粒定量分析技术及原理、系统组成和软件设计。测试结果表明,该法操作简便、测试速度快、重复性好。     

基于图像分析方法的颗粒粒度测量

为了满足颗粒粒度测量的要求,研究开发了基于颗粒图像的颗粒体粒度测量系统。系统由硬件和软件两部分组成。硬件系统主要由图像采集和显示设备构成,可完成颗粒图像采集、存储和显示功能。软件系统由自主开发的基于Matlab环境的颗粒图像处理与分析程序组成,可完成颗粒图像的处理、颗粒粒度分析及分析结果显示等功能。颗粒测量结果表明,该系统完全可以满足颗粒粒度测量的要求,并具有测量精度高、效率高等特点。     

激光散射法中折射率对粒度结果的影响

用激光散射法测量粒度时,要考虑引入折射率,本文讨论了它对粒度结果的影响。     

AgBr颗粒大小的UV测量及应用研究

针对生产过程中使用激光粒度仪测量AgBr颗粒粒径分布过程中测量结果经常出现偏离测量标准的问题,对激光粒度分布仪测定AgBr颗粒粒径分布过程中,颗粒的散射过程基于Mie散射理论进行了理论计算和分析。理论分析表明产生偏离测量标准的原因主要是AgBr颗粒的复折射率和AgBr颗粒晶型的影响造成的。实验室利用双注乳化技术制备了X1、X2、X3型三种不同粒径大小的AgBr立方体颗粒乳剂,并用紫外分光光度法(UV)对乳剂颗粒进行了表征。实验表明:AgBr颗粒乳剂的特征吸收峰位与颗粒大小存在一定的线性关系,这种线性关系反映了颗粒平均粒径的大小。对X3型不同批次乳剂进行了粒径分布统计和特征吸收峰位测量,粒径分布统计表明X3型乳剂颗粒体积平均径变化范围为0.620～0.690μm,相对应的特征吸收峰峰位变化范围为383～403 nm,并用线性方程表征了两者之间的关系。提供了一种测量AgBr乳剂颗粒大小的新方法,对判断问题乳剂有重要的指导意义,对常规颗粒大小的测量方法完善提供了重要的参考价值。     

颗粒形状对全散射法测量颗粒物质量浓度的影响

燃煤电厂排放颗粒物作为大气颗粒物主要来源之一受到广泛关注,实现颗粒物质量浓度的精确在线监测意义重大。激光全散射法作为一种常用的颗粒物质量浓度在线监测方法,受颗粒特性影响较大,易造成较大的测量偏差。为探究颗粒形状对全散射法测量的影响,搭建了全散射法测试台架,并采用球形二氧化硅颗粒对测试系统进行标定,标定结果显示,球形二氧化硅颗粒质量浓度与消光程度高度线性相关,相关系数R2>0.99,测量浓度与真实浓度偏差仅为1.8%。进一步采用633 nm与532 nm波长激光分别对3种非球形(棱形、不规则和片状)二氧化硅颗粒进行测试试验。测试结果显示,3种形状颗粒物的质量浓度与消光程度均高度相关,R2均高于0.99;3种形状颗粒物质量浓度的测量值与真实值偏差与颗粒形状及激光波长相关,对比发现,入射波长为633 nm时,不规则、棱形和片状颗粒的质量浓度测量值与真实值的测量偏差分别为16.1%、27.4%和36.6%;入射波长为532nm时,3种颗粒质量浓度的测量偏差分别为4.8%、11.4%和17.4%;颗粒形状一致条件下,532 nm入射波长时的测量偏差明显较小,通过波长的选择可降低颗粒形状变化造成的测量偏差。     

炭素粉末颗粒粒度的测量方法及原理

本文介绍了五种炭素粉末颗粒粒径的测量方法及各自原理。五种方法为：显微镜法、消光法、电传感法、全息照相法和激光光散射法。     

Application of Particle Measurement Technology in Process Intensification

The competitive pressure in the chemical industry makes it necessary to take measures that enable processes to be drastically improved in order to remain competitive also in the future. For the development and implementation of such process‐intensive measures, it is expedient to perform a complete analysis of the process of interest. This approach is demonstrated using a size reduction process for a particulate active substance as an example. Correlations between the dispersion characteristics and quality characteristics of the product were found using two complementary methods of particle measurement technology, ultrasonic spectroscopy and laser diffraction. These methods make it possible to analyze the efficiency of the comminution apparatuses, but also of the processes. Ultrasonic spectroscopy can be used as a measurement method for local process control.     

CFD Model of Particle Agglomeration in Spray Drying

A 3D CFD model of the agglomeration of droplets and particles in a counter-current spray-drying process was developed and verified. An original discrete phase model was elaborated, with an agglomeration module taking into account hydrodynamic segregation of particles, droplet coalescence, and droplet shrinkage for accurate calculations of mass balance of the discrete phase. The characteristic drying curves were applied to the model of particle moisture evaporation, which included the coupling of particle agglomeration with heat, mass, and momentum transfer between the discrete and continuous phases. Two agglomeration zones were observed in the tower: wet particle agglomeration in the atomization zone, and “dry agglomeration” above the air inlets, due to the intensive mixing of particle streams. A comparison of the calculated particle size distributions and experimental data obtained from particle dynamics analysis (PDA) measurements proves the accuracy of the developed methodology. The elaborated model allows the final PSD of the powder in the spray towers to be predicted.     

颗粒增强复合材料热膨胀系数预测模型的研究现状

针对颗粒增强复合材料热膨胀系数经典和新近出现的性能预测模型进行了总结,讨论了研究热膨胀系数需要考虑的基本问题,对Kerner、Turner、Wang and Kwai、Schapery、Park、Sideridis、李燕、倪新华、石连生、陈康膨胀系数预测模型的代表性体积单元的选取、基本假设和适用条件进行了归纳,并对膨胀系数的进一步的研究提出了一些看法。     

Prediction of Particle Deposition Using a Simplified Particle Model in Fully Developed Channel Flow

In this study the Eulerian particle model was modified to predict the particle deposition rate in fully developed channel flow. The modified model is less complicated and has much lower computation time. The performance of the simplified model was examined by comparing the particle deposition rate in a vertical channel with the experimental data for fully developed channel flow available in the literature. The effects of turbophoretic force, thermophoretic force, electrostatic force, gravitational force, Brownian/turbulent diffusion, and the wall roughness on the particle deposition rate were examined. The predictions of the modified particle model were in agreement with the experimental data.     

Numerical Simulation of Liquid-Solid Countercurrent Fluidization inside an Extraction Column Based on Particle Trajectory Model

The liquid–solid countercurrent fluidization process in an extraction column was numerical y simulated based on the particle trajectory model of Eulerian–Lagrangian method. The simulation approach was ...     

Particle Image Velocimetry of a Swirling Fluidized Bed at Different Blade Angles

The particle motion within a stable swirling operation regime of a fluidized bed is investigated. Particle image velocimetry was used to elaborate the hydrodynamics of multi‐sized particles fluidized at different air distributor blade angles. The experimental results revealed that the superficial velocity is the most prominent aspect affecting the hydrodynamics of a swirling fluidized bed (SFB) followed by the bed weight, particle shape, and blade inclination angle. Particles of different sizes and shapes fluidized well in the SFB which emphasizes its superiority over contemporary techniques. The slug‐wavy regime in the SFB is promising and has considerable potential, especially for diffusion‐controlled reactions and processes in the industry. The particle velocity increased with air flow rate at shallow bed height but decreased with bed weight.     

Particle shape and orientation in laser diffraction and static image analysis size distribution analysis of micrometer sized rectangular particles

Laser diffraction (LD) and static image analysis (SIA) of rectangular particles [United States Pharmacopeia, USP30-NF25, General Chapter <776>, Optical Miroscopy.] have been systematically studied. To rule out sample dispersion and particle orientation as the root cause of differences in size distribution profiles, we immobilize powder samples on a glass plate by means of a dry disperser. For a defined region of the glass plate, we measure the diffraction pattern as induced by the dispersed particles, and the 2D dimensions of the individual particles using LD and optical microscopy, respectively. We demonstrate a correlation between LD and SIA, with the scattering intensity of the individual particles as the dominant factor. In theory, the scattering intensity is related to the square of the projected area of both spherical and rectangular particles. In traditional LD the size distribution profile is dominated by the maximum projected area of the particles (A). The diffraction diameters of a rectangular particle with length L and breadth B as measured by the LD instrument approximately correspond to spheres of diameter Ø_L and Ø_B respectively. Differences in the scattering intensity between spherical and rectangular particles suggest that the contribution made to the overall LD volume probability distribution by each rectangular particle is proportional to A²/L and A²/B. Accordingly, for rectangular particles the scattering intensity weighted diffraction diameter (SIWDD) explains an overestimation of their shortest dimension and an underestimation of their longest dimension. This study analyzes various samples of particles whose length ranges from approximately 10 to 1000 μm. The correlation we demonstrate between LD and SIA can be used to improve validation of LD methods based on SIA data for a variety of pharmaceutical powders all with a different rectangular particle size and shape.     

The Presence of Adsorbed Proteins on Particles Increases Aggregated Particle Sedimentation,as Measured by a Light Scattering Technique

Protein conformational changes are often induced when bound to surfaces and can modulate colloidal stability of protein coated particles in dispersion. We evaluated bovine serum albumin (BSA) adsorbed onto polystyrene particles at room temperature. A z-axis translating laser light scattering device (ZATLLS) measured the sedimentation velocity of protein-coated particles tracking aggregation characteristics compared with non-coated ones. Sedimentation velocities of particles moving in the dispersion, and the resulting viscosity and density of the residual solution following sedimentation determined aggregate size in the dispersion using Stoke's law. Our experiments objectively show that albumin-coated polystyrene forms aggregates. Interestingly, coating particles with protein slows the sedimentation velocity which should correspond to a more dispersed system, but it leads to higher aggregate sizes due to the larger influence of proteins in solution raising solution viscosity. Protein-bound particles were observed to fall out of solution in a more controlled and steady manner compared with uncoated particles.     

A Simple Analytical Model for Reactive Particle Ignition in Explosives

A simple analytical model is developed to predict ignition of magnesium particles in nitromethane detonation products. The flow field is simplified by considering the detonation products as a perfect gas expanding in a vacuum in a planar geometry. This simplification allows the flow field to be solved analytically. A single particle is then introduced in this flow field. Its trajectory and heating history are computed. It is found that most of the particle heating occurs in the Taylor wave and in the quiescent flow region behind it, shortly after which the particle cools. By considering only these regions, thereby considerably simplifying the problem, the flow field can be solved analytically with a more realistic equation of state (such as JWL) and a spherical geometry. The model is used to compute the minimum charge diameter for particle ignition to occur. It is found that the critical charge diameter for particle ignition increases with particle size. These results are compared to experimental data and show good agreement.