消光起伏光谱的时间相关处理

消光起伏光谱法(TFS)是一种新的颗粒测量方法,可同时测量两相流中颗粒的粒径分布和体积浓度。由于在测量原理和结构上非常简单,这种方法可用来实现在线、实时测量。然而在实际测量中,消光起伏光谱法对颗粒粒径分布的分辨率还比较低且对高浓度颗粒系的测量须考虑颗粒相互作用效应。本文提出一种新的数据处理方法-消光起伏相关光谱法(TFCS),通过对消光起伏信号在不同相关时间参数下进行相关计算来得到消光起伏光谱以提高消光起伏法对颗粒粒径分布的分辨率。     

基于二阶滤波器的消光起伏谱颗粒测量结果

消光起伏频谱法是一种新的测量两相流系统中颗粒粒径分布和浓度的方法,装置简单,操作方便,适合实时、在线测量。采用二阶低通滤波器对起伏的透射率信号分析,得到消光起伏频谱实验数据,并利用改进的Chahine循环方法计算得到颗粒的粒径分布和浓度信息。重点讨论高浓度情况,包括对特征函数频率响应的修正和对其阶高修正两个方面,得到修正参量并运用到反演算法中从而得到正确的测量结果。测量结果表明,通过高浓度修正,消光起伏频谱法可以在很大的颗粒浓度动态范围得到合理的测量结果,其可测颗粒最大体积分数视颗粒的大小而定。     

利用消光起伏信号测量颗粒平均粒径

窄光束照射流动颗粒系时,透过率会产生起伏.起伏的透过率信号可用来测量颗粒平均粒径和浓度.由于在测量原理和结构上非常简单,这种方法可用来实现在线、实时测量.Gregory提出的数据处理模型要求光束直径较小而且远大于颗粒直径,本文提出一种新的模型,可在光束直径接近甚至小于颗粒直径情况下对透过率起伏信号进行处理,模拟分析和实验测试表明,该方法可得到较满意的测量结果.     

无限细光束中透射起伏时间相关频谱法高浓度效应的模拟

时间或空间相关透射起伏频谱法是近年发展起来的一种新的颗粒测量方法,它可同时测量颗粒粒径分布和浓度,并可用来进行在线、实时测量。研究表明,随着浓度增大,逐渐增强的高浓度效应会导致测量值越来越严重地偏离理论值。本文采用模拟计算方法讨论无限细光束照射下的时间相关透射起伏频谱法高浓度效应并给出部分实验验证。分析表明,无限细光束照射时的透射起伏相关频谱主要受到层结构效应的影响,颗粒交叠效应不明显,表明为随着颗粒浓度增大,转换函数(特征函数)逐渐偏离低浓度理论值并向无因次相关时间小的方向移动,阶高始终保持不变。     

基于带通滤波器的透射率起伏信号频谱特征

透射率起伏频谱测粒技术是根据透射光起伏信号的频谱特征发展起来的一种新的颗粒测量方法,可用于实时在线测量。研究基于一阶带通滤波器的透射率起伏信号的频谱特征,重点分析带通滤波器带宽因子对透射率起伏频谱及其反演结果的影响。同时还考虑了无因次光束直径对透射率频谱的影响。结果表明选择较小的带宽因子α有利于提高测量结果的颗粒粒径分辨率,但是带宽因子α过小会降低透射率起伏频谱的强度从而导致测量产生误差;反之,选择较大的带宽因子α有利于获得较强的透射率起伏频谱信号,但是带宽因子α过大会降低测量结果的颗粒粒径分辨率。     

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。     

风沙流中颗粒相浓度和粒度的瞬态同步测量

本文基于激光衍射技术提出了一种新的浓度测量的改进方法。该方法可以同时获得测量颗粒的浓度和粒径分布。基于这一测量方法,通过对大型风洞风沙两相流系统中不同风速,高度条件下颗粒浓度和粒径测量,获得了跃移颗粒的空间结构信息。结果显示,颗粒浓度随来流风速线性增加,且在近床面区域内来流风速对颗粒粒径具有选择性。     

跨微米尺度混合颗粒粒径的同步测量方法

基于多波长消光法和图像法颗粒测量原理,提出了跨微米尺度混合颗粒粒径同步测量方法,建立了亚微米-十微米尺度颗粒粒径消光光谱反演算法及十微米以上尺度颗粒粒径图像处理算法;采用分光棱镜,搭建了消光光谱与背光图像同步测量装置,利用500 nm～76.9μm粒径范围内的10种标准颗粒配成跨微米尺度混合颗粒样品并开展实验研究。结果表明:利用所提方法开展跨微米尺度混合颗粒粒径同步测量时,亚微米-十微米尺度颗粒消光光谱与十微米以上尺度颗粒背光图像的相互影响可忽略,可同步测量得到跨微米尺度混合颗粒粒径;利用消光法和图像法分别开展亚微米-十微米、十微米以上尺度颗粒粒径测量,与标准颗粒粒径相比,相对误差均小于8%,且测量重复性较好,这为跨微米尺度混合颗粒提供了一种有效的粒径测量手段。     

单光束互相关法测量高浓度纳米颗粒粒径

针对光子相关光谱法不能测量高浓度纳米颗粒粒径和双光束互相关测量法装置结构过于复杂等问题,提出了一种基于范西特-泽尼克定理的单光束互相关法。首先分析了传统双光束互相关法存在的问题,然后根据范西特-泽尼克定理建立了单光束互相关测量法的模型,设计完成了单光束互相关颗粒粒度测量装置,最后对各种浓度不同粒径的颗粒进行了测量。实验证明,单光束互相关法能有效抑制多重散射的影响,适用于测量高浓度纳米颗粒粒径。     

基于图像动态光散射的二维纳米颗粒粒度测量

提出了一种基于图像动态光散射原理测量二维纳米颗粒粒度的新方法,称为平移转动-图像动态光散射(TR-IDLS)法。采用会聚的偏振高斯光束照射样品池中处于布朗运动的二维纳米粒子,分别采集纳米粒子的水平偏振散射光信号和垂直偏振散射光信号。根据两个偏振方向上散射光光强波动的时间相关函数,计算出纳米颗粒的平移和转动扩散系数的分布,进而从扩散系数中获得颗粒的长宽比、等效直径和厚度的分布。采用该方法测量了球形标准纳米颗粒和片状云母颗粒的粒径。采用电镜获得了片状云母颗粒的形状和等效直径,并与TR-IDLS方法的实验结果进行比较,验证了TR-IDLS方法的可行性。     

Measurements on Particle Size Distribution and Concentration by Transmission Fluctuation Spectrometry with Temporal Correlation

Transmission fluctuation spectrometry with temporal correlation (TFS‐TC) is a new method for particle analysis. When a narrow light beam irradiates on a particle dispersion flow, the variation of the number of particles in the small measuring zone will cause the transmitted light to fluctuate, which includes the complete information on both particle size distribution (PSD) and particle concentration. The method may be used for real‐time, inline/online applications due to its simplicity of measuring principle and experimental setup. Until recently, the theory has been limited to low particle concentrations. In this work, an experimental study of the TFS‐TC measurement is presented for a very wide range of the particle concentrations. By introducing an empirical correction including the high concentration effects and considering the effect from rheological conditions in the inversion algorithm, the particle size distribution and particle concentration are reconstructed, resulting in the coverage of a broad range of particle size and concentration.     

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.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions Part One: Effects of the Monolayer Structure

The theory of transmission fluctuation spectrometry (TFS) was recently developed for particle size analysis in dilute flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution and particle concentration.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions. Part Three: Measurements

The theory of transmission fluctuation spectrometry (TFS) was developed for particle size analysis in flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution (PSD) and particle concentration. In the previous parts of this publication high concentration effects on TFS were investigated theoretically and by simulation. This work presents a study on TFS measurements in concentrated suspensions. By introducing an empirical correction to include the high concentration effects from both the monolayer structure and particle overlapping in the inversion algorithm, it is possible to obtain the particle size distribution and particle concentration over broad ranges of particle sizes and concentrations.     

Measurements of particle-size distribution and concentration by transmission fluctuation spectrometry with temporal correlation

A new method of transmission fluctuation spectrometry with signal correlation was recently developed for particle-size analysis, whereby both particle-size distribution and particle concentration can be measured simultaneously. The measurements were realized with temporal correlation of the transmission fluctuation signals of a focused Gaussian beam.     

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 %.     

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.