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.     

Intercomparison of Inversion Algorithms for Particle‐Sizing Using Mie Scattering

The applicability of different inversion algorithms to retrieve a size distribution of particles in air from light scattering is examined. The investigation is focused on an optical measurement setup with an elliptical mirror as the main optical element. In order to evaluate the capabilities of the individual inversion methods, light scattering by spherical particles is simulated in the size ranges of 0.1 – 10 μm and 0.05 – 1 μm. The distribution of the particle diameters is modeled with three different parametric functions, i.e., RRSB, logarithmic‐normal and a more specific distribution from an ultrasonic nebulizer. Different kinds of noise, e.g., additive and/or multiplicative, are applied in different levels to the simulated scattering measurement to include real physical measurement conditions. The convergence properties of the scattering simulation are investigated with respect to the number of size classes, and thus, information concerning the size resolution required to simulate a measurement for a given particle size distribution is obtained. Further parameters of interest are the minimum angular resolution of the measurements, the number of size classes of the retrieved particle size distribution and the measured polarization of the scattered 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.     

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.     

组织模型偏振后向散射差分光谱的测量

建立了一套用于测量生物组织模型偏振后向散射差分光谱的实验系统。在系统中,线偏振光入射到样品表面,检偏器和光谱仪配合记录后向散射光中的平行和垂直分量,随后计算出差分光谱。采用了平均直径分别为5.0μm、9.0μm的两种聚乙烯小球悬浮液进行实验,结果与蒙特卡罗模拟进行对照,验证了实验系统的正确性。初步研究了粒子尺寸分布变化对差分光谱的影响,结果表明,偏振散射差分光谱能敏感地反映粒子尺寸分布的变化,在大小粒子的混合液中,大粒子浓度一定程度的增加,光谱仍保留小粒子的振荡趋势,但差分光强减小。该方法对于早期癌症检测具有潜在应用意义。     

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.     

可见-红外波段光全散射法颗粒粒径测量范围的研究

在光全散射法颗粒粒径测量中,采用独立模式算法在可见-红外波段对粒径测量范围进行了深入的研究。通过对多种R-R分布函数反演结果进行分析,比较,以确定光全散射法颗粒粒径测量范围。同时在消光系数计算中,采用修正的消光系数代替原始的消光系数,以便得到更准确的粒径测量范围。仿真计算结果表明,在可见-红外光谱区,相对折射率m=1.235时的粒径测量范围为0.05～18 μm。在此区域内测量粒径分布,反演结果与真值基本吻合。随着颗粒相对折射率、波长范围的变化,粒径测量范围也随之发生改变。采用限制最小二乘算法能够最大限度地克服随机噪声对测量结果的影响,使测量的精度和可靠性明显提高。对测量的消光值加入±1%随机噪声时,颗粒粒径分布的反演均能得到满意的结果。     

真实加工表面后向散射特性分析及表面参数反演

无合作目标激光绝对测距中,远距离、真实表面的后向散射特性机理不明朗,严重影响测距结果,是制约测距技术发展的重要瓶颈。以立铣、平铣、平磨等三种典型实际机械加工方式下的粗糙表面为研究对象,测量了在1 550 nm红外激光照射下形成的后向散射场,探究了不同加工方式下特殊后向散射场形成的原因,深入分析了表面纹理、入射方位角、入射角度、粗糙度对后向散射场分布的影响。实验结果分析表明,加工制造表面的后向散射光谱形态分布受加工方式的影响很大,且相互入射几何关系和粗糙度对每种加工方式下的实际粗糙表面均有规律性影响。为了能够获取足够的后向散射能量,对表面参数的识别反演显得十分重要。进一步构建了一种加工表面多维参数反演模型,采用另外一种加工方式(刨床)的样块数据进行验证,加工方式能够被准确区分,入射方位角和粗糙度反演的相对误差分别达到1.21%和1.03%,反演精度较高。经实验验证,通过表面参数的反演极大拓宽了无合作目标激光绝对测距的范围,有效降低了表面纹理、入射方位角、粗糙度等对测距范围的影响。这一研究结果还对具有纹理特征加工表面的后向散射光谱的研究和在其他领域的应用均具有一定的参考价值。     

Light scattering properties of sea-salt aerosol particles inferred from modeling studies and ground-based measurements

Direct climate radiative forcing depends on the aerosol optical depth τ, the single scattering albedo ?, and the up-scatter fraction β; these quantities are functions of the refractive index of the particles, their size relative to the incident wavelength, and their shape. Sea-salt aerosols crystallize into cubic shapes or in agglomerates of cubic particles under low relative humidity conditions. The present study investigates the effects of the shape of dried sea-salt particles on the detection of light scattering from the particles. Ground-based measurements of scattering and backscattering coefficients have been performed with an integrating nephelometer instrument for a wavelength . The measurements are compared to two models: the Mie theory assuming a spherical shape for the particles and the Discrete Dipole Approximation (DDA) model for the hypothesis of cubic shape of the sea-salt aerosols. The comparison is made accurately by taking into account the actual range of the scattering angles measured by the nephelometer in both models that is from 7° to 170° for the scattering coefficient and from 90° to 170° for the backscattering coefficient. Modeled scattering and backscattering coefficients increase for nonspherical particles compared to spherical shape of particles with diameter larger than about 1 μm. However, the comparison of the modeling results with the measurements gives best agreement for particles diameter less than about 1 μm. The size distribution of the particles is measured with two instruments with different size bins: an electrical low-pressure impactor (ELPI) and an aerodynamic particle sizer (APS). It is found that the size of the bins of the instruments to determine the number concentration of the particles in accordance with their diameter is critical in the comparison of measurements with modeling.     

Variations in Grain Size Analysis with a Time‐of‐Transition Laser Sizer (Galai CIS‐50) using a Gravitational Flow System

This study deals with grain size analysis with a Laser Sizer Galai CIS‐50. This device utilizes the time‐of‐transition method and is equipped with a module for measurements in the range 0.5 to 150 μm along with a gravitational flow system. Experiments were conducted using natural marine sediments. The aim was to determine possible explanations for discrepancies in the measured results that occurred between different operators of the Galai CIS‐50. These discrepancies may be due to differences in the technique of inserting a sub‐sample into the measurement system. Furthermore, the influence of the sample concentration and the flow velocity in the device's liquid flow cell is considered, since these factors can act as potential sources of inaccuracies and errors in the experimental setup. Strong variations in the results occurred, which were mainly due to problems in the detection of particles >20 μm. In the range>20 μm gaps appeared in the registration of the size distribution. An improvement in reproducibility was achieved by using a pipette instead of a beaker for the insertion step. Nevertheless, the standard deviation for mean grain sizes of natural marine sediments obtained with the Galai CIS‐50 is still about 20%.     

A Method for Increasing the Sensitivity of Phase Doppler Interferometry to seed particles in liquid spray flows

A method has been developed to increase the sensitivity of phase Doppler interferometry-based particle sizing systems to small particles in the presence of a spray containing large and small droplets; an important consideration when using seed particles to track the gas-phase velocity in multi-phase flows. The method, applicable to PDPA systems configured to operate in first and higher order refraction mode, involves doping the sprayed liquid with a dye that is strongly absorbing at the incident laser wavelengths. This results in greatly diminished scattered intensity from larger droplets, thus allowing the photomultiplier gain to be set to a level sufficient to easily detect small particles without saturation. Tests conducted indicate that, at a collection angle of 30° and droplet absorptivity of γ = 0.014/μm, the PDPA can accurately size absorbing droplets up to approximately 200 μm. This upper limit can be extended by changing selection angle. Tests performed with an actual spray demonstrated that the method allowed detection of 1 μm to 235 μm droplets; more than four times the instrument's usual range of 50: 1. A data correction scheme to determine the effective probe volume radius for each particle size class has been developed for absorbing particles, as standard correction schemes derived for non-absorbing droplets excessively weigh distributions toward smaller particles.     

The Measurement of Particles Suspended in a stirred vessel using microphotography and digital image analysis

A novel technique to determine the size of particles suspended in a stirred vessel is investigated. The method uses microphotography to obtain a still image of the particles in situ. The equivalent circular diameter of the particles is obtained from the photographs using digital image analysis. The particles used for the test were certified particle size standards of a very small tolerance in diameter deviation. The size comparison was determined as a percent error between the measured particle diameter (equivalent circular diameter) and the diameter established by the particle manufacturer. To determine the limiting ranges of particle size and concentrations, spherical particles in a size range of approximately 1 to 10.0 μm (microns) in diameter were employed in the test. Concentrations varied from 0.00005% to 0.1% (mass basis). For each particle size, an aqueous solution of the particles was prepared at the desired concentration and placed in a stirred vessel. Photographs of the solutions were made at 25.5x, 40x, 60x and 80x magnification. For all sizes of particles, the entire range of concentration was examined. The results indicate a minimum size resolution of approximately 3μm, in a corresponding concentration range of 0.0001% to 0.05%. Similar limits on concentration were found for the larger diameter particles, although a true upper limit for the largest particle sizes was not established. The functional concentration range appears to shift towards higher mass concentrations with increasing particle size. For 2.92 μm diameter particles, the error in size measurement was found to be below 10% for a concentration range of 0.0005% to 0.05%. Additionally, a relationship between turbidity and the error was seen at low particle concentration levels where decreasing levels of turbidity generated increasing levels of error.     

沙丘粗糙面的二次极化电磁散射

研究了新月形沙丘粗糙面的二次极化电磁散射. 结合射线追踪理论, 由一次散射面元的反射场照射到二次散射面元, 采用基尔霍夫近似推导了二次散射面元的二次极化散射场. 计算结果表明二次极化散射结果在特定的角度和类型范围内有显著影响. 在电磁波射向背风坡时可以发现其同极化散射截面在入射角较大时大于其他入射方向的结果, 入射角在休止角附近时的交叉极化散射截面出现峰值, 以及前后狭长沙丘之间的二次极化散射特别突出. 本文结果可用于反演分析沙漠地区的风场信息. 关键词： 新月形沙丘 二次极化散射 射线追踪 休止角     

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.     

Study on the Relationship between Particle Size and Near Infrared Diffuse Reflectance Spectroscopic Data

Since the particle size distribution is a critical parameter of pharmaceutical excipients used for tablet manufacturing by direct compression, the mean particle size of sieved sorbitol powder was studied by near‐infrared diffuse reflectance spectroscopy (NIRDRS). The aim of this study was to investigate the effect of the particle size (reciprocally proportional to the bulk density) on the reflectance spectrum. The effects of the particle characteristics on the spectral changes were described on the basis of the Kubelka‐Munk theory taking the scattering into consideration. A smaller particle size fraction was associated with a lower spectral value, and at the characteristic wavelength of 1584 nm a linear relationship was established for the particle size range from 125 to 670 μm. The diffuse reflectance measurement was sensitive to the particle characteristics, which offers a fast, non‐destructive alternative test method that can be applied after detailed calibration.     

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 %.     

基于组合拟合法的冰晶粒子的光散射计算

利用组合拟合法计算了冰晶粒子的单次散射特性。给出了消光效率因子、单次散射反照度及非对称因子的拟合公式,利用拟合公式对有效粒子尺度为20μm和120μm的六种冰晶粒子的消光效率因子、单次散射反照度及非对称因子进行了计算。结果表明,粒子的消光效率因子、单次散射反照率和非对称因子随着入射波长的增加有着较大的起伏,后两者随着波长的增加而变化趋势基本一致;对于单次散射反照率来说,在可见光波段,反照率非常接近于1;在短波段,粒子的非对称因子变化较小,并且随着波长的增加,非对称因子会逐渐增大。     

Transient Response of Particle Distribution in a Chamber to Transient Particle Injection

We inject a large number of newly created nano‐particle aggregates into a chamber for the purpose of removing harmful contents in an indoor environment. This study is to experimentally and numerically investigate transient response of particle distributions to particle injections. A room‐sized chamber of 4 m × 2.1 m × 2.4 m is connected to a specially designed particle‐injection system, with two Optical Particle Counters used to simultaneously measure particle‐number densities with the size range from 0.3 μm to 10 μm at the inlet and in the chamber. A velocity probe measures the flow that is up to 1 m/s. An Euler‐type particulate‐phase‐transport model is developed and validated by comparing with experimental data. The study shows that the transient behavior of particle distributions is determined by many factors, including particle size, particle settling speed, sampling location, and velocity distribution. Particle number densities decrease in time more quickly for large particles than for small particles, and locations farther downstream in the chamber correlate more weakly with the inlet injection.     

Effects of nondiffusive wave propagation upon coherent backscattering by turbid media

The nondiffusive contribution to the coherent backscattering intensity is calculated for the media with relatively large particles (size a is greater than wavelength λ). The results are in good agreement with the experimental data at the wings of the angular spectrum of the coherent backscattering. The shape of the backscattering peak is analyzed for strongly absorbing media. The correlation function of the intensity fluctuations is calculated for the scattering by Brownian particles at relatively large time shifts.