Simultaneous Measurement of Particle Size and Particle Velocity by the Spatial Filtering Technique

The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity.     

Multidimensional Particle Size Distributions and Their Application to Nonspherical Particle Systems in Two Dimensions

Particle science and technology evolve toward ever increasing complexity with respect to the multidimensional particle properties of size, shape, surface, internal structure, and composition. In this study, the theoretical background is elaborated for multidimensional particle size distributions (PSDs) by transferring the concepts known from 1D size distributions to anisotropic particles comprising at least two different length dimensions, e.g., nanorods and platelets. After introducing 2D PSDs, the calculation of differently weighted probability density functions including their interconversion is presented. This is necessary in order to compare data resulting from different measurement techniques which probe different physical properties and thus provide differently weighted PSDs. In addition, it is shown how 1D distributions with reduced content of information can be deduced from 2D PSDs. As a proof‐of‐concept and for illustration purposes, this approach is applied to a 2D Gaussian size distribution. Furthermore, a generalized scheme is suggested which outlines the conversion of number, surface, and volume weighted densities within the 2D space. The application of these methods to the more general n‐dimensional case is straightforward.     

Inlet Efficiency Study for the TSI Aerodynamic Particle Sizer

The paper reports on the particle. sampling efficiency of the inlet system for the Aerodynamic Particle Sizer (TSI, Inc., St. Paul MN). Large particles are depleted from the sampled aerosol by two mechanisms: super-isokinetic sampling at the entrance of the inlet, and inertial impaction on the inner nozzle. A fluorometric technique was used to separately characterize these mechanisms. Numerical studies were also performed. The experimental results show that the inlet's overall efficiency drops from around 90% for 3 μm particles to less than 45% for particles larger than 10 gm. Several high efficiency inlets were developed and tested. These inlets provide higher sampling efficiencies, but reduce the instrument's sizing resolution. Measurements of 7.3 μm oleic acid particles with a high efficiency inlet showed a 5% spread in measured diameter at 50% count, while less than a 1076 spread was observed using the standard inlet. It was also found that the super-isokinetic condition reduces particle losses on the inner nozzle. The standard inlet is recommended for verifying test aerosol monodispersity. An alternative to the standard inlet is suggested for measurement of size distributions.     

Design and Performance Evaluation of Low‐Volume PM2.5 Inlet for Analyzing Chemical Composition

A new PM_2.5 inlet, based on the particle cup impactor configuration, was designed for sampling fine particles smaller than 2.5 μm in aerodynamic diameter and for operating at a flow rate of 5 l/min, as the devices, which are used to analyze the chemical composition of the particles, have good efficiency only at low‐volume flow rates. The performance of the inlet was evaluated in a test chamber, and the optimum dimensions of the particle cup impactor were determined by varying the nozzle‐to‐cup distance. Additional experiments covering flow rates between 3 and 10 l/min with particle sizes between 0.8 and 5.0 μm were carried out in the test chamber. The performance indicated that a nozzle‐to‐cup distance of 1.1 mm would yield a sharp size cutoff. The results from the tests showed that the inlet had a cutoff size of 2.55 μm in aerodynamic diameter at a flow rate of 5 l/min.     

Particle tracking velocimetry applied for fireworks

Particle tracking velocimetry (PTV) is applied for measuring the motions of luminous particles in fireworks. The objective of the study is to clarify the technical problems encountering in large-scale quantitative visualization in natural environment. The major problems are found to be uncontrolled background in nature, low pixel resolution relative to particle size, and large perspective. The ways to deal with these problems in current technological level are discussed. In the application, two cameras are located at 1.3 km from the launching point with 30-degree opening angle to implement 3-D PTV. The transient 3-D velocity distributions of around 200 m-scale diameter fireworks are obtained during the light emission from the explosion till burnout. Moreover, the evolution of the mean particle diameter that decreases continuously with the combustion is estimated with the measured velocity information by the particles equation of motion.     

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。     

冲击波作用下微米尺度金属颗粒群的动力学行为

基于平面化爆驱动飞片高压加载技术和激光测速技术,研究了冲击波加载不同粒径锡颗粒群的微喷射行为以及在空气中的减速规律.实验结果表明,锡颗粒的最快喷射速度随粒径增大而显著增大.通过对微喷射形成过程的三维光滑粒子流体动力学方法数值模拟发现,大粒径锡颗粒之间存在较大的空隙结构,冲击波与空隙结构的相互作用诱导产生高速汇聚射流,空隙结构越大对应的喷射速度也越高.此外,通过研究不同粒径颗粒在复杂流场中的减速规律,进一步深化了对微喷射破碎后的颗粒尺度状态以及混合输运特性的认识.研究结果对于预测和分析冲击波加载微米颗粒群的微喷混合特性具有一定价值.     

Particle Size Classification of Glass Particles Using Aerodynamic Jet Vectoring

An experimental demonstration of a new, non‐contact particle characterization technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows–flows that are a fraction of the jet flow rate–to sharply change the direction of a planar, particle‐laden jet. As the jet is vectored, particles present in the flow experience a resultant drag force, dependent upon their size, that balances inertia. Since this balance determines the particle's trajectory, vectoring the flow leads to a separation of particles downstream. This simple, low‐pressure‐drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices. Particles from 10–40 μm and 2.5 times the density of water have been sorted to an accuracy of 1.5 μm. Sorting of heavy particles such as these is accomplished at very low speeds, reducing the tendency of damage to the particles. Lighter particles are sorted at higher speeds. Particles from 5–40 μm and 0.6 times the density of water were sorted to an accuracy of 6.6 μm. AVPS is also shown to be capable of concentrating aerosols. Our measurements indicate that an air sample containing water‐like particles can be concentrated by a factor of 10 using AVPS.     

Fractional Penetrations for Electrostatically Charged Fibrous Filters in the Submicron Particle Size Range

Particle penetrations through commercially available, electrically charged fibrous filters have been measured. The particles were monodisperse and in charge equilibrium. Tests were conducted for several particle sizes in the range 0.02 μm ≤ x ≤ 1 μm. The face velocity was varied in the range of 2 cm/s to 30 cm/s. The penetration has a bimodal dependence on particle size. This behaviour is not found for uncharged filters. The reduction in penetration and bimodal dependence is attributed to electrical collection effects. As the face velocity is increased, the electrostatic collection effects are significantly reduced. The results agree quantitatively with a model for particle penetration through charged fibrous filters recently presented in the literature by the authors.     

Characterization of Particle Size Standard NIST 1019b with Synchrotron X‐ray Microtomography and Digital Data Extraction

We show that synchrotron x‐ray microtomography (μCT) followed by digital data extraction can be used to examine the size distribution and particle morphologies of the polydisperse (750 to 2450 μm diameter) particle size standard NIST 1019b. Our size distribution results are within errors of certified values with data collected at 19.5 μm/voxel. One of the advantages of using μCT to investigate the particles examined here is that the morphology of the glass beads can be directly examined. We use the shape metrics aspect ratio and sphericity to examine of individual standard beads morphologies as a function of spherical equivalent diameters. We find that the majority of standard beads possess near‐spherical aspect ratios and sphericities, but deviations are present at the lower end of the size range. The majority (> 98 %) of particles also possess an equant form when examined using a common measure of equidimensionality. Although the NIST 1019b standard consists of loose particles, we point out that an advantage of μCT is that coherent materials comprised of particles can be examined without disaggregation.     

Particle Shape Investigations with a light-scattering optical instrument

A light-scattering instrument that is normally used for particle size analysis was applied to obtain information about particle shape. Micro-cuboids of dimensions a × b × c in the range between 10 and 1000 μm, which can be accurately manufactured employing special technology, were used as labelled samples for the determination of 3-D features. Particle projections at different orientations due to turbulent motion were measured sequentially. The laser diffraction of cuboids rotating in a turbulent flow is described theoretically using a simplified model, i.e. rotation of a rectangle. The change in the projection areas of rotating cuboids is connected with their rotational velocity. The power spectrum density of rotational velocity of cuboids and spheres was determined and the influence of particle shape on the power spectrum density established. The frequency distribution of projection sizes was found to be suitable for particle shape estimation.     

Analysis of Single Particle Attrition during Impact Experiments†

Particle breakage can be characterised as attrition, chipping, fracture, abrasion and wear. All these types of breakage mechanisms are the effect of the damage caused to these particles. These mechanisms can be differentiated not just on the basis of magnitude and direction of the force but also by the damage caused to the particles. The damage is measured by change in the size distribution and the change in shape of the particles. In the current research, experiments were performed on the newly developed Repeated Impact Test. The unique feature of this test is that about hundred particles can be subjected simultaneously to a monitored number of impacts, without particle‐particle interactions at regulated velocities. The preliminary experiments were performed with single crystalline particles of different shapes and sizes. After fixed number of impacts, the images of the particles were taken. The volume and shape of the particles were determined by image analysis. It was observed that the rate of attrition was very high when the particles are irregular. The rate decreased as the particles became more spherical.     

Experimental Study on Particle Size Distribution and Concentration Using Transmission Fluctuation Spectrometry with the Autocorrelation Technique

Based on the statistical characteristics of the transmission fluctuations in the particle suspension, transmission fluctuation spectrometry with autocorrelation (TFS‐AC) is described theoretically, with the assumptions of geometric ray propagation and completely absorbent particles in the suspension. The experiments presented here are realized in a focused Gaussian beam with the TFS‐AC technique. The acquisition of transmission fluctuation signals is achieved by using a high‐resolution digital oscilloscope. The transition function of TFS‐AC is obtained by varying the autocorrelation time. With a modified iterative Chahine inversion algorithm, solving a linear equation retrieves information on the particle size distribution and particle concentration. Some experimental results on spherical and non‐spherical particles are presented and discussed. The experiments cover a particle size range from 1μm to 1000 μm and a particle concentration of up to 12 %.     

YAG : Ce3+发光粉的粒度与LED匹配性

研究了不同粒度的YAG : Ce³⁺发光粉对LED亮度的影响,结果显示:粒度越大,封装后LED亮度越高;造成这种结果的主要原因是发光粉颗粒的晶格完整性不同。计算了发光粉在硅胶中的沉降速度,数据说明粒度越大,沉降速度越快,也就越不利于点胶。综合以上两个方面的结果认为发光粉的颗粒不宜太粗或太细,而且分布应该尽可能的窄,10~20 μm是粒径的理想范围。     

Particle Mass Loading Effect on a Two-Phase Turbulent Downward Jet Flow

The particle mass loading effect on the flow structure of a two-phase turbulent jet flow was studied. A particle mass loading ratio ranging from 0 to 3.6 was used as the control parameter. The polystyrene solid particles used had nominal diameters of 210 and 780 μm. The flow Reynolds number, which was based on the pipe nozzle diameter and the fluid-phase centerline mean velocity, was 2 × 10⁴ in the current test. A two-color laser Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed to measure the mean velocity distributions for the particle and fluid phases, and the turbulent intensities and Reynolds stresses of the flow. The two-phase jet flow field was measured from the initial pipe exit to 90 D downstream. Another one-component He? Ne laser LDA system was also applied to obtain the energy spectra and temporal correlations of the two-phase jet flow.     

Particle Size Analysis by Transmission Fluctuation Spectrometry: Experimental Results Obtained with a Gaussian Beam and Analog Signal Processing

Transmission fluctuation spectrometry (TFS) is a method for the analysis of particle size distributions based on the statistical fluctuations of a transmission signal. Complete information on the PSD and particle concentration can be retrieved by a special transformation of the transmission signal, whereby the expectancy of the transmission square (ETS) is determined after the signal has been subjected to a procedure of spatial and temporal averaging. By varying the averaging parameters over a wide range, a spectrum of ETSs is obtained and introduced into a linear equation system, which yields the PSD. In the experimental realization presented here, variable temporal averaging is realized in the frequency domain with a series of low pass filters at different cutoff frequencies while spatial averaging inevitably occurs as the particles pass through a focused Gaussian beam of finite cross section. Experimental results on spherical particles (glass beads) and non‐spherical particles (SiC) are presented. The PSDs are resolved in 30 intervals within a particle size range from 1–1000 μm, employing a modified Chahine inversion algorithm. So far, the measurements are limited to moderate particle concentrations. Some influences affecting the measurements, especially for higher particle concentrations, are discussed in detail.     

Size and Shape Analysis of Sedimentary Grains by Automated Dynamic Image Analysis

The application of Automated Dynamic Image Analysis (ADIA) for measuring the size and shape of sedimentary grains is presented. This technique determines the size and shape of a large number of particles (typically 5,000 to 50,000 or greater) in the size range between 10 to 1,500 μm. ADIA measurements are carried out using a RapidVue particle analyzer. The size and shape of particles are obtained by analyzing digital images. Each image is composed of shapes representing two‐dimensional projections of particles. The analysis yields the area and perimeter of each particle cross‐section, which are transformed into size‐independent shape values. The analysis of such a large number of particles results in a very small statistical variation of the results, ca. 0.3% for 50,000 particles. Since operator selection of images does not enter the measurement procedure, the risk of bias caused by subjective sample selection is eliminated. The combination of ADIA with a two‐dimensional Kolmogorov‐Smirnov test, allows the identification of similarities and differences between sedimentary grains.     

Theoretical studies on particle shape classification based on simultaneous small forward angle light scattering and aerodynamic sizing

Particle shape contributes to understanding the physical and chemical processes of the atmosphere and better ascertaining the origins and chemical compositions of the particles. The particle shape can be classified by the aspect ratio,which can be estimated through the asymmetry factor measured with angularly resolved light scattering. An experimental method of obtaining the asymmetry factor based on simultaneous small forward angle light scattering and aerodynamic size measurements is described briefly. The near forward scattering intensity signals of three detectors in the azimuthal angles at 120?offset are calculated using the methods of T-matrix and discrete dipole approximation. Prolate spheroid particles with different aspect ratios are used as the shape models with the assumption that the symmetry axis is parallel to the flow axis and perpendicular to the incident light. The relations between the asymmetry factor and the optical size and aerodynamic size at various equivalent sizes, refractive indices, and mass densities are discussed in this paper. The numerically calculated results indicate that an elongated particle may be classified at diameter larger than 1.0 μm, and may not be distinguished from a sphere at diameter less than 0.5 μm. It is estimated that the lowest detected aspect ratio is around 1.5:1 in consideration of the experimental errors.     

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.     

Size Measurement of Very Small Spherical Particles by Mie Scattering Imaging (MSI)

The Mie Scattering Imaging method (MSI) gathers out‐of‐focus images of dispersed spherical particles present in a laser light sheet and extracts the individual particle diameter from these images. The general idea of the method has been around for more than a decade and a number of papers has dealt with it over recent years. Our work focuses on small particle sizes from 20 μm down to 2 μm, a range which has not been tackled so far although it is of great importance in particle systems. We present an optical set‐up with a special arrangement of camera lenses that allows to work in this range. An evaluation algorithm based on correlation of the experimental optical information with theoretical Mie scattering was found to give the most accurate results for particle sizing. Besides accuracy measurements on solid spheres the versatility of the method is demonstrated by an example of transient droplet growth between 2–7 μm.