Development of a Method for the Measurement of Particle Size and Velocity based on Projection onto a Variable Frequency Grating

Irregular particles down to approximately 3.8 μm have been sized by imaging them onto a variable frequency grating using laser illumination. Velocity can also be determined. The method was successful for certain particle types that were rough or irregular, partly absorbing or translucent. It was not successful for transparent spheres that display glare spots in the image, or other particles that produce localised regions of high brightness.     

基于线阵CCD空间滤波效应的航空相机像移速度测量方法

基于空间滤波测速原理,提出了利用线阵CCD空间滤波效应进行航空相机像移速度测量的新方法。对线阵CCD输出图像进行隔行采样,模拟了多狭缝的空间滤波特性,实现了对航空相机像移速度的光学非接触测量。通过研究空间滤波器的功率谱密度函数,对影响线阵CCD空间滤波特性的关键因素进行了特性分析,并在实验上验证了利用线阵CCD推扫图像模拟多狭缝空间滤波器测量像移速度的可行性。结果表明,对于5～53.2 mm/s范围内的像移速度,测量误差导致的像移量误差不大于1/3 pixel,能够满足航空相机像移补偿精度的要求。     

Bubble Velocity and Size Measurement with a Four‐Point Optical Fiber Probe

The possibility to measure the velocity and size of individual bubbles in a high‐void fraction bubbly flow is investigated by using a four‐point optical fiber probe. The air bubbles have an initial spherical equivalent diameter ranging from 4 to 10 mm and the void fraction is up to 0.3. Firstly, single bubble experiments show that intrusiveness effects, i.e. bubble deformations due to the probe, are negligible provided that the bubble approaches the probe at the axis of the central fiber. A selection criterion is utilized for multiple bubble experiments. A good compromise can be found between the required accuracy, the duration of the measurements and the number of validated bubbles required for reliable statistical averaging. In an air‐water high‐void fraction vertical bubbly pipe flow, the void fraction obtained with the instrument is found to be in good agreement with both local single‐fiber probe measurements, and with the volume average void fraction obtained from pressure gradient measurements. The area average volumetric gas flow rate, based on the bubble velocity and void fraction as measured with the four‐point probe, agree with the measured gas flow rate. Also, the liquid velocity is measured by means of a laser‐Doppler anemometer, to investigate the slip velocity. The results show that reliable and interesting measurements can be obtained by using a four‐point optical fiber probe in high void fraction flows.     

Simultaneous Measurement of Droplet Size and Three-Components of Velocity in Spray

The combination of the optical diagnostics and image processing technique has produced various methods of practical measurement in engineering. The measurement of size and velocity of droplets in fuel spray is one typical example. In general, the spray is a complicated and three-dimensional two-phase flow; therefore multi-dimensional field measurement of the spray field is indispensable. In the present paper, a technique of simultaneous measurement of droplet size and three-components of velocity is proposed and applied to spray issuing from the swirl nozzle as a practical application. The focused image of glare points is captured by a stereoscopic arrangement, and droplet size and the three-components of velocity are evaluated from the doublet image. Fundamental optical arrangements to capture the image of the glare points with a stereo view are established, and the feasibility and the accuracy of the technique are confirmed. © 2004 The Optical Society of Japan     

固体激光器热透镜焦距的自适应补偿

It is suggested an improved method for measuring the velocity distribution of cold atoms, using FM technique to derive the signal from the recoil-induced resonance. The method is capable to measure velocity distribution of atoms cooled below the Doppler limit of laser cooling in a compact space with high S/N ratio.     

Locally Resolving Measurements of PSD,Particle Concentration and Particle Velocity by Means of TFS with Dual Beams

Transmission fluctuation spectrometry with spatial correlation (TFS‐SC) is based on transmitting two beams of radiation through a flowing suspension, whereby the distance of the beam centers is varied. Thus, the spatial correlation of the transmission fluctuations of the two beams is determined as a function of the beam distance. By numerical modeling, the transition functions of the correlation are found as a function of beam distance, beam diameters, particle diameter and beam intersection angle. Experimentally determined spatial correlation spectra can be inverted to obtain the particle concentration and particle size distribution by using the theoretical transition functions for mono‐sized particles. In addition, time correlations can be used to extract information on particle velocity. Some experimental results obtained by TFS‐SC are presented and discussed. This method appears promising for application in the local resolving of measurements of PSD, particle concentration and particle velocity in two‐phase flows, both in the laboratory and in process control.     

乙醇喷雾场粒子尺寸和速度的数字全息测量

利用连续波激光器和高速CCD,采用数字同轴全息系统,记录了乙醇喷雾粒子场全息图.对粒子场再现像进行聚焦像合成,自适应滤波、二值化、Roberts边缘提取,Hough变换和亚像素精度计算,得到粒子的直径和位置信息.利用两次曝光记录的两个序列全息图得到粒子位移,进而求得粒子的运动速度,给出了实验结果.研究结果表明,该实验系统可用于内燃机喷雾场测量,且具有光路系统简单、成本低等特点.     

A Novel Device for Single Particle Light Scattering Size Analysis and Concentration Measurement at High Pressures and Temperatures

Based on the findings of previous work, a novel instrument was developed for the size analysis and concentration measurement of particles dispersed in gases at high temperatures (600 °C) and pressures (16 bar). The main motivation for the construction of this device was a measurement requirement at the conditions of a pressurized pulverized coal combustion (PPCC) test installation in Dorsten, Germany. The development of a high efficiency (> 50 %), coal based, combined cycle process, and specifically, the development of efficient gas cleaning technology for gas combustion under demanding conditions (1400 °C and 16 bar) was the main target. A suitable measurement technique was required for the determination of particle size and concentration downstream of the gas cleaning equipment, which is able to operate close to the given conditions. The performance of the novel device was tested in several measurement series with various monodisperse aerosols at ambient conditions as well as in high pressure, high temperature situations with very satisfactory results, i.e., the lower detection limit (50 % counting efficiency at ca. 0.3 μm) and resolution of the novel device are comparable to state of the art instruments (of the same principle) intended for room temperature operation.     

Estimating Average Particle Size by Focused Beam Reflectance Measurement (FBRM)

The Lasentec focused beam reflectance measurement (FBRM) probe provides in situ particle characterisation over a wide range of suspension concentrations. This is a significant advantage over conventional instruments that require sampling and dilution. However, FBRM gives a chord distribution, rather than a conventional diameter distribution. Both theoretical and empirical methods for converting from chord to diameter data are available, but the empirical method was found to be more successful.     

Analysis of Particle Size Distribution by Particle Tracking

Particle tracking is performed using a combination of dark field or fluorescence video microscopy with automatic image analysis. The optical detection together with the image analysis software allows for the time resolved localization of individual particles with diameters between 100 and 1000 nm. Observation of their Brownian motion over a set of time intervals leads to the determination of their mean square displacements under the given room temperature and viscosity. Hereby, the radii of a set of particles visible within a given optical frame are derived simultaneously. Rapid data analysis leads to reliable particle size histograms. The applicability of this method is demonstrated on polystyrene latices and PMMA nanospheres with radii between 51 nm and 202 nm.     

A Double Gaussian Beam Method for the Determination of Particle Size,Direction and Velocity

This paper describes a technique aimed at measuring particle size by light scattering from gaussian laser beams. The uncertainties in illumination due to the beam shape are avoided by determination of the direction and velocity. The method, which we arbitrarily called the Two Beam System (TBS), uses a simple birefringent prism to separate the incident laser beam into two orthogonally polarised overlapping parallel beams. The relative delay and amplitudes of the intensities scattered out of the orthogonal polarisations are indicative of the particle direction and velocity. Having obtained the direction of travel of the particle, its size is then obtained from the scattered intensity using Mie theory.     

窗函数对光学空间滤波效果的影响分析

为改善光学空间滤波的效果,分析说明了低通滤波器窗函数对光学空间滤波效果的影响。提出了相同通频区域下选择窗函数的两个要求即更窄的频谱主瓣宽度和更小的旁瓣高度,并运用MATLAB模拟了基于4f系统的光学空间滤波。结果表明,窗函数频谱主瓣宽度直接影响滤波结果的轮廓可见度,频谱旁瓣直接影响着频域截断带来的吉布斯波纹的大小。为如何选择滤波器透过率分布提供了理论参考。     

Measurement of Solid-gas Two-phase Flow using Optical Fiber Sensor

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On‐line Determination of Particle Size Distributions in Flowing Dispersions

Emulsions are of great importance to industry. They are involved in many engineering operations, including chemical reactions, extraction, emulsification and suspension polymerization, etc. However, an important problem for these processes is how to control the size distribution of the dispersed phase. Indeed, off‐line analysis of the emulsion may generate uncertainties due to sampling and dilution of the product, which are likely to change the dispersion state and physico‐chemical properties. In this work, an on‐line optical method is proposed to characterize dispersed media in real flowing conditions. This method is based on the time‐analysis of back‐scattered light fluctuations. The present paper deals with the development of this method and its application to dispersions of alumina in water. The results obtained with the on‐line optical method are compared with those acquired by classical laser light scattering and microscopy.     

激光尘埃粒子计数器微型光学传感器的研究

研制成功便携式激光尘埃粒子计数器的核心部件———微型光学传感器。该传感器采用直角散射光收集形式,以高功率半导体激光器作为光源,同时采用高性能的PIN型光电二极管作为光电探测器。散射光收集系统为单一大数值孔径的球面反射镜,其对粒子散射光的收集角范围从20°到160°。粒子散射光信号是脉冲信号,其频谱成份主要在高频段,所以在PIN型光电二极管后用一个带通式前置放大器来消除外界的低频噪声,根据米氏散射理论计算了该光学传感器的光散射响应特性,并用聚苯乙烯标准粒子实测了该光学传感器的性能。结果表明,该系统具有高的信噪比、计数效率和尺寸分辨本领。     

用双周期光纤光栅实现温度和应变的同时测量

介绍了光纤光栅传感器的一般原理，分析了长周期光纤光栅和Bragg光纤光栅的应变和温度响应机理。结果表明，长周期光纤光栅和Bragg光纤光栅的温度和应变灵敏度不仅与纤芯参数和光栅周期有关，还依赖于包层参数。在同一根光纤上先后写入长周期光纤光栅、Bragg光纤光栅，利用长周期光纤光栅和Bragg光纤光栅基模与包层模耦合时温度和应变灵敏度的不同，实现应变和温度的同时测量。     

A Displacement and Velocity Measurement Technique Using Millimeter-Wave Sensor

In this paper, a millimeter-wave sensor is presented for measurement of displacement and velocity. By using monolithic microwave integrated circuits and digital quadrature sampling signal-processing scheme, the sensor operating at 60 GHz is implemented. Polynomial curve-fitting technique is used for the error correction. Digital quadrature mixer is also configured as a phase-detecting processor, which enables low Doppler frequency to be measured with high resolution. Measured displacement results indicate resolution and maximum error of 10 μm and 30 μm, respectively, and measured speed is as low as 30 mm/s, corresponding to 6.6 Hz in Doppler frequency, with an estimated velocity resolution of 3.3 mm/s. To the best of our knowledge, the attained resolution and maximum error are the best reported results.     

激光干涉测速技术在内弹道弹丸速度测量中的应用研究

 利用任意反射面激光干涉测速（VISAR）系统以及全光纤位移干涉仪（FDI）,测量了线膛炮弹丸速度,获得了线膛炮弹丸在0~491 μs内从零加速到140 m/s的速度历史,弹丸运动了20.7 mm,出炮口时的弹丸速度为817 m/s。实验结果表明,影响激光干涉测速技术在内弹道测量中应用的主要因素是炮口烟。研究结果对于深入探索激光干涉测速技术在内弹道测量中的应用有重要的参考意义。     

利用双周期光纤光栅实现应变和温度同时测量

提出了一种新颖双周期光纤光栅传感器。在同一段氢载光纤上先后写入长周期光纤光栅、短周期布拉格光纤光栅 ,利用长周期光栅和布拉格光栅对应变和温度敏感性的差异 ,可实现应变和温度的同时测量。实验中采用这种灵敏结构的双周期光栅 ,在 0～ 170 0 με和 2 0℃～ 12 0℃范围内 ,测量精度可达到± 16 με和± 0 8℃。     

海水盐度和温度实时检测的新型光纤传感器研究

提出了一种新颖的用于海水温度和盐度同时实时探测的光纤传感器系统。分别利用半导体材料吸收光谱的临界极限值随温度变化发生移动而导致出射光强改变的特性和待测液体盐度变化引起传输光折射角改变导致接收端光线偏移的性质，通过反射式的结构设计和线阵排列的接收光纤信号传输至海面以上，并由CCD实现对光强峰值信号及其偏移量的采集。传感器由一直角棱镜、本征GaAs单晶体薄片、装有参考液和待测液的水槽、接收光纤阵列等部分组成。理论分析和仿真结果验证了传感器设计的可行性。