Particle Sizing by Planar-Phase Doppler System

Conventional phase Doppler systems are useful for sizing particles in the order of microns, but sensitive to the Gaussian beam defect which can cause sizing errors. The defect can be significant when a large size is measured. In this paper, we present a new phase Doppler system using a planar optical layout which permits large particles to be measured in a forward scattering scheme without the Gaussian beam errors. The optical system design is discussed by numerical simulation based on the Mie theory.     

Characterization of Pyrogenic Powders with Conventional Particle Sizing Technique: II. Experimental Data

When the impact of an aggregate's structure on its physical properties is adequately accounted for, it is possible to use those properties for quantifying the structure. A recent paper [1] has discussed such structure‐property‐relationships for pyrogenic powders. Based on them a calculation scheme is proposed that allow the analysis of size distributions from Dynamic Light Scattering (DLS) and Optical Centrifugation Analysis (OCA) with regard to the translational hydrodynamic diameter, the diameter of gyration and the aggregation number. The scheme includes the conversion from optically weighted to number weighted distributions. The performance of this calculation scheme is tested for different grades of fumed silica, which were analyzed by two DLS and one OCA instrument. A fairly good agreement is observed with regard to medians of the distribution functions. The paper shows that differences in size distributions obtained by different measurement techniques may not only explained qualitatively but can even quantitatively traced back to distribution functions of structural aggregate parameters.     

A CONTIN-Based Approach Towards the Data Analysis of Particle Sizing Experiments by Centrifugal Photosedimentometry

In order to analyse the output data of centrifugal photosedimentation experiments using CONTIN software, a mathematical model has been derived. This model is based on Fick's second law and describes the sedimentation behaviour of monomodal particles in a centrifugal field: it predicts that the extinction at the detection point decays exponentially until the particles are sedimented past the detection point, which gives a sharp drop of the curves to the baseline. In practice, however, a more fluently decaying profile was obtained. Simulations revealed that the polydispersity of the sample was responsible for this behaviour. When centrifugal photosedimentation data for effective monomodal and bimodal samples of fairly monodispersed PMMA lattices were analysed with CONTIN, using the model proposed, accurate particle size distributions were obtained, provided that the sample cell was completely filled. This was imperative in order to minimize the deviations of the practical application as compared with the theoretical model.     

Particle Sizing Using Frequency Domain Photon Migration

The transport properties of particulate process streams and their final product quality, are directly affected by critical parameters of particle size distribution, f(x), and volume, mass, or number density of particles or dispersed phase droplets. A method is proposed for the potential on-line monitoring of particle size distribution and volume fraction in real time, using frequency-domain photon migration measurements (FDPM). Theory, experimental measurements, and results for the determination of particle size distributions for both a polystyrene latex and a titanium dioxide suspension determined using the photon migration technique are presented. The critical issues associated with the application of photon migration to particulate and dispersed phase processes are discussed, including the effects of interparticle interactions on the transport of light.     

On the Sizing Accuracy of Laser Optical Particle Counters

The performance of a narrow-angle and a wide-angle, forward scattering laser aerosol spectrometer has been studied as a function of particle size and refractive index. The results have been compared with theoretical calculations based on light scattering theory. The results indicate that for the narrow-angle instrument, the scattered-light intensity is not a monotonic function of particle size for transparent particles (a monotonic relationship is required for unambiguous particle size measurement) above 0.7 μm. The instrument is therefore limited in its useful range to size distribution measurement between 0.2 μm – its lower particle size limit – and 0.7 μm for transparent particles. In the case of the wide-angle instrument, the instrument output is a monotonic function of particle size for transparent particles, but the output is severely attenuated for light absorbing particles above 0.3 μm. The instrument, therefore, cannot be used for accurate size measurements above 0.3 μm for light absorbing particles.     

Phase-Doppler Particle Sizing with Off-Axis Angles in Alexander's Darkband

A promising optical layout for standard phase-Doppler particle sizing instruments for use in two-phase flows with extremely limited optical access is presented. When applied to turbine oil of variable temperature and therefore refractive index (1.40< n < 1.46), the layout procedure leads to several suitable off-axis configurations. From these, a backscatter angle of ? = 125° is chosen owing to several geometrical restrictions. Although this angle lies in Alexander's darkband and therefore the intensities are low, the theoretical analysis indicates that this configuration is extremely insensitive to Gaussian-beam defects, which usually aggravate backscatter applications. Monosized droplet experiments confirmed the application of the configuration and showed an acceptable accuracy of the measurements. Experiments in a bearing chamber test rig gave reliable results and for the first time allowed an insight into the flow phenomena of this highly complex technical two-phase flow.     

透过率起伏光谱分析法测粒技术

提出的透过率起伏光谱分析法是一种新的颗粒测量方法。采用一细小光束照射匀速流动的颗粒系统,通过采集透射光起伏信号,经统计处理得到透过率的平均值与起伏谱。通过求解逆问题,从透过率的起伏谱中得到颗粒粒径分布信息,再结合透过率的平均值得到颗粒的体积分数信息。给出了关于单层颗粒透过率的平均值与起伏谱的理论表达式,并推广到三维单分散和多分散的颗粒系统。对粒径在32~425μm内的稀薄颗粒系进行了部分实验测试和模拟计算,结果表明该方法可同时对颗粒粒径分布和体积分数进行有效测量。     

CONTIN算法及其在测量微凝胶颗粒粒度分布中的应用

颗粒粒径大小决定了微凝胶的相变行为,因此采用有效可靠的手段来确定胶体悬浮液中颗粒的平均粒径及粒度分布是至关重要的。CONTIN算法是分析动态光散射实验数据,获取胶体悬浮液中颗粒粒度分布的有效算法,但目前的最优正则化参数选取策略依赖于颗粒粒度分布的先验条件。为此,本文提出利用V-曲线准则获取最优正则化参数,使用CONTIN算法表征微凝胶悬浮液颗粒系的平均粒径和粒径分布信息。实验结果表明,与V-曲线正则化参数选取准则相结合,利用CONTIN算法可以有效的获取微凝胶悬浮液的颗粒粒度信息。     

高浓度超细颗粒的后向光子相关光谱测量技术研究

针对光子相关光谱颗粒粒径测量法不能在线测量高浓度超细颗粒的问题,通过分析溶液浓度对光子相关光谱测量法的影响,设计了一种后向散射光路,提出了后向光子相关光谱测量法.实验采用50 nm、100 nm以及500 nm三种标准乳胶球颗粒,在不同的浓度下分别用两种方法进行了测试.结果证明,后向光子相关光谱测量法能有效抑制多重散射的影响,适用于高浓度超细颗粒粒径的在线测量.     

用全固态激光器和一维CCD测定微粒粒径

建立了一套利用线阵CCD探测散射光强从而测定粒径的实验装置.该装置采用线阵CCD取代传统的同心环探测器,并采用一台小尺寸全固态绿光激光器取代传统的He-Ne激光器.理论上采用全Mie氏散射理论,自行编写了实验数据的计算机拟合程序,可以由实验测得的散射光强角分布反演求出粒径分布信息.对粒径分别为4.91 μm和9.88 μm的聚苯乙烯小球均取得了良好的粒径测量结果.该装置被证实可用于测定的粒径范围为0.7 μm～44.0 μm.     

Particle Sizing in a Flow Environment Using Light Scattering Patterns

This study introduces measurements of light scattering intensities individually produced from polystyrene micro‐spheres illuminated by focused Gaussian beams in a flow environment. These light scattering signatures are correlated to the particle size. The Fourier domain information of the light scattering signatures are interpreted and translated to recover the dimension of each particle. A hardware‐software interface is designed to capture, analyze and interpret the collection of various scattering light intensities. A major contribution of this study is in consolidating the implementation of the Lorenz‐Mie theory with the experimental results of collected light scatterings for the purpose of particle sizing through novel pattern analysis techniques. In so doing, a synergetic approach is considered in bringing together the hardware design with the software implementations for an integrated hardware‐software interface.     

基于单模光纤的DLS粒径测量研究

动态光散射技术是一种测量纳米颗粒粒径分布的最有效方法。为了克服高浓度样品溶液中存在的多重散射效应, 本文基于单模光纤搭建了一套DLS实验系统, 传输光纤的输出端与接收光纤的接收端都作了抛光磨平处理。在模拟复杂工业环境下, 分别用低浓度单分散、不同浓度单分散以及高浓度多分散性标准聚苯乙烯乳胶球悬浮液检测了该系统的适用性。实验结果表明, 利用该系统可快速准确的测量体积分数达40%的聚苯乙烯乳胶球悬浮液中的纳米颗粒粒径及其分布。     

Evaluation of a Particle Sizing Technique Based on Laser Sheets

The use of a laser sheet (or elliptical Gaussian beam) in meas-urement techniques is of growing interset. Some of these techniques take advantage of the wavefront curvature of such beams as in a dual-crylindrical wave system (DCW). Nevertheless, up to now, the analysis of the properties of the light scattered by spherical particles form the beam has been carried out largely by using geometrical optics or classical Lorenz-Mie theory. In this paper, the generalized Lorenz-Mie theory (GLMT) is applied to the analysis of an existing DCW measurement system. Differences between the results predicted by classical approaches and by GLMT are emphasized.     

用于光子相关光谱颗粒粒度测量的实数编码混合遗传算法

提出一种自动缩小反演范围的实数编码混合遗传算法,并用于光子相关光谱颗粒粒度测量中.该算法利用混沌遍历性质,融入模拟退火算法,具有较强的局部搜索能力.通过数值模拟,讨论在无噪声和多种噪声水平影响下单分散颗粒系的反演结果;分析90 nm聚苯乙烯标准颗粒样品的实验测量数据.结果表明,反演的粒径分布在峰值位置、峰宽度、峰对称性等方面很接近颗粒的真实分布,具有较强的抗噪声干扰能力.     

PCS颗粒测量技术中的累积分析方法研究

采用Levenberg-Marquardt法对累积分析方法中初始值的选择问题进行了分析和研究,并采用此方法对50 nm,100 nm,200 nm,300 nm,500 nm的标准聚苯乙烯乳胶颗粒的实测数据进行了拟合,通过与传统的累积分析法拟合结果对比,采用Levenberg-Marquardt法改进的累积法不但可以给出稳定的颗粒粒径,而且减小了拟合结果的误差.     

Reflection Phenomena in Particle Sizing by static and dynamic light scattering

Using a monodisperse poly(methyl methacrylate) dispersion it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influence of reflection on DLS experiments was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the SLS and DLS techniques.     

High-Resolution Phase Doppler Particle Sizing based on Hilbert transform signal processing

A new phase Doppler anemometry (PDA) signal processing method based on a Hilbert transform algorithm is introduced and analysed. By generating a 90° phase-shifted burst signal in the time domain, the envelope of the Doppler burst can be determined. In addition, this envelope is approximated by a Gaussian exponential function. The difference of the maxima of these Gaussian approximations for two related PDA bursts gives an estimate of the time difference between these time shifted signals. With the introduction of this estimation method, the restriction to the [0,360°] interval resulting from conventional signal analysis may be avoided in many cases. To investigate the dependence on SNR, burst position, burst frequency and sampling rate, results of computer simulations are presented. The feasibility of the method is demonstrated briefly by experimental results. Phase differences of more than 2000° arising from the measurement of monodisperse droplets by a conventional PDA setup could be determined.     

Sizing of Submicron Aerosol Particles by the Whisker Particle Collector Method

Samples of an alumina powder aerosol were collected on whisker particle collectors and analysed following an improved evaluation scheme which allows the empirical size distribution to be corrected for the effect of a non-uniform collection efficiency. The measurement results are given in terms of log-normal distribution functions. Some ambiguity was encountered in interpreting particle aggregates that were found on the whisker collectors. By including the results of laser light-scattering experiments in the size analysis, this ambiguity was removed. Advantages and disadvantages of the whisker collector concept compared with light-scattering methods are discussed.     

Laser Diffraction Spectroscopy: Influence of Particle Shape and a Shape Adaptation Technique

The evaluation algorithm employed in laser diffraction spectroscopy is usually based on the Fraunhofer diffraction theory for spheres. As this evaluation theory is limited to spheres only, the measurement of irregularly shaped particles results in errors in the evaluated particle size distribution. To determine the influence of the particle shape, measurements of arbitrarily shaped particles were simulated, evaluated and compared with results for spherical particles of the same projected area. The detailed investigations showed that the particle's microstructure, i.e. its surface roughness, has almost no or only a negligible effect on the measurement result. In contrast to this advantageous outcome, the particle's microstructure, i.e. its axis ratio, affects the measurement result greatly and must be taken into account in the evaluation method. Based on these results, particles were considered to be ellipsoids with specific (but negligible) surface structures and a mathematical adaptation method was developed by extending the evaluation theory from spheres to randomly in space oriented ellipsoids. Simulations and experiments with reticles verified the need for this adaptation technique and its efficiency when applied.