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。     

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。     

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.     

基于多重散射的卷云辐射传输特性

采用空间离散化,并利用散射矩阵方法计算了卷云在3．72tim和6．85tim波长上的辐射传输特性,研究了卷云的冰晶粒子形状、组分和光学厚度等因素对卷云的辐射传榆特性的影响。仿真结果表明,随着平均冰晶尺度的增加,卷云的反射函数会逐渐减小;对于不同形状,但具有相同最大粒子尺寸的粒子组成的卷云,反射函数也会有所不同;随着光学厚度的增加,卷云的反射函数会逐渐增大,直至饱和,而透射函数逐渐减小;随着太阳天顶角的增大,卷云的反射函数逐渐增大。透射函数逐渐减小。     

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.     

Transmission Fluctuation Spectrometry with Spatial Correlation

Transmission fluctuation spectrometry (TFS) is being developed as a new method of particle size analysis. In the early approaches, the particle suspension was illuminated by one beam with finite beam diameter and the transmission signals underwent a process with variable spatial and/or temporal averaging and a subsequent nonlinear operation. The transmission fluctuations were obtained as a spectrum which included the information on particle size distribution and particle concentration. A new approach presented here employs two narrow parallel beams. While changing the beam separation, the transmission fluctuations of these two beams are expressed in terms of the expectancy of the transmission product (ETP). The analytical expression of the ETP through a monolayer is derived and the ETP of a 3‐dimensional suspension is formulated based on the layer model. The deviation between the transition functions of 3‐dimensional suspensions and monolayers is found to be affected by effects from particle overlapping and monolayer structure.     

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 %.     

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。     

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。     

自悬浮定向流技术中铜纳米微粒的粒度控制研究

 采用自悬浮定向流技术制备了金属铜纳米微粒，根据TEM的行貌像对样品平均粒度进行标定，并结合样品制备的条件对制备工艺进行了研究。结果表明，自悬浮定向流技术可以方便地制备出不同粒度的金属铜纳米微粒，微粒平均粒径随熔球温度的降低而减小，随冷却气体流速的增大而减小；在1 200℃下微粒平均粒径随惰性气体压强的增大而减小，而在1 300℃时惰性气体压强对微粒平均粒径的影响不再具有规律性。     

消光起伏自相关频谱法颗粒测量技术

消光起伏相关频谱法(TFCS)是一种新的颗粒测量方法。采用一束窄光束照射两相流系统,照射区中颗粒浓度的起伏所导致的透射光起伏信号中包含了颗粒的粒径和浓度信息,对光束的透过率信号作相关处理得到消光起伏相关频谱,可用来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。本文介绍消光起伏自相关频谱的测量原理,并给出部分实测结果。     

Characterization of energy barrier and particle size distribution of lyophilized ferrofluids by magnetic relaxation measurements

The magnetic properties of a ferrofluid are strongly influenced by its particle size distribution. We analyzed a ferrofluid with an unknown particle size distribution as well as fractionated samples of the original material. The ferrofluid in our investigations consists of a mixture of maghemite and magnetite. We investigated these different samples using temperature-dependent magnetorelaxometry method. The evaluation of the Néel relaxation signal allows us a direct determination of the energy barrier distribution, which is one of the most important parameters of such systems of magnetic nanoparticles. The calculated particle volumes were compared with particle sizes determined by transmission electron microscopy.     

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.     

Multi-lognormal soot particle size distribution for time-resolved laser induced incandescence in diesel engines

In-cylinder and exhaust soot particle size measurements were carried out using time-resolved laser induced incandescence and electrical mobility spectrometer techniques in a single cylinder optical diesel engine and multi-cylinder high-speed diesel engine. The temporal decay of the laser induced incandescence signal from a polydisperse nanoparticle ensemble of soot during transient diesel combustion is shown to be described by both a single-lognormal distribution as well as multi-lognormal size distribution. However, a multi-lognormal particle size distribution is introduced in the existing model for a comprehensive characterisation and realistic reconstruction of the size distribution. Detailed theoretical analysis of multi-lognormal size distribution along with its application to the experimentally measured soot particle size is validated in this work. These results were also qualitatively compared and independently verified by the experimental results obtained by the electrical mobility spectrometer and published transmission electron microscopy data. These findings reveal that the in-cylinder and the exhaust soot particle size distributions in engines are better represented by a multi-lognormal size distribution.     

The Fundamentals of Particle Size Analysis by Transmission Fluctuation Spectrometry. Part 1: A Theory of Temporal Transmission Fluctuations in Dilute Suspensions

The extinction of radiation in suspensions is traditionally described by the Bouger-Lambert-Beer law (BLBL). Based on a quasi-continuum approach, the BLBL does not account for the discrete nature of particles or their spatial extension and arrangement. If an extinction measurement is made with a high spatial and temporal resolution, the transmitted intensity signal shows significant fluctuations. The strength of fluctuation is related to the physical properties of the suspension and the process of spatial and temporal averaging. Exploiting this connection, it is possible to calculate the particle size distribution and the particle concentration from transmission measurements. This part of the series of papers provides a method for the temporal decomposition of the transmission's power spectrum, which permits the information on the particle size and concentration to be extracted from the seemingly irregular fluctuation of the transmission signal.     

颗粒系的可见消光光谱分析及最佳波长的选择

在光全散射法颗粒粒径测量中,被测颗粒系的消光光谱包含有颗粒粒径、折射率等信息。对常用的单峰及双峰R-R分布的可见消光光谱进行模拟,分析了可见消光光谱随粒径和相对折射率变化的规律。选取二阶微分可见消光光谱不连续点对应的波长作为测量波长,并将可见光边界波长同时作为测量波长,在非独立模式下,采用遗传优化算法反演粒径分布。仿真计算与实验验证结果表明,通过消光光谱分析,可以预先确定被测颗粒系的分布状况,缩小优化算法中反演参数的搜索范围。结合最佳波长选择方法,使测量的精度和可靠性明显提高。对测量光谱加入1%随机噪声时,单峰及多峰分布粒径反演均能得到满意的结果。     

Scattering and Transmission by a Monolayer of Spheres: A Study on the Monolayer Structure

The angular distribution of scattered light and the transmission of radiation through a monolayer of monodisperse spherical particles at variable particle concentration are studied. The scattering of light by a single particle is calculated with the classical Lorentz‐Mie theory. For a monolayer of mono‐dispersed spherical particles, if the monolayer density is less than 0.5 and the particle size parameter is larger than 5, effects from multiple scattering and dependent scattering can be excluded so that only steric interactions are considered. It is found that the scattering pattern, especially in the forward and backward directions, and the transmission are strongly dependent on the monolayer density.     

电爆炸制备纳米铜粉及物相研究

采用电爆炸法制造纳米金属颗粒。分析了铜丝在电爆炸过程中的物态变化,即从固态、液态、气态到离子态;同时理论研究了纳米铜粉粒径大小及分布、成分组成与爆炸时的能量、铜丝的直径和铜丝长度的关系;定义了粒径均匀度,通过粒径平均大小和粒径均匀度比较,分析了纳米粒径的大小分布情况;通过X射线衍射仪(XRD),透射电子显微镜(TEM)对电爆炸制造出的纳米铜颗粒做了测定与定量分析。结果表明:铜粉的主要成分由氧化铜、氧化亚铜及单晶铜组成,各成分所占比例与爆炸缸内的真空度相关。纳米金属微粒的粒径平均值、粒径均匀度与铜丝长度、直径、充电电压、放电时间等因素相关。     

A Rapid Method for Growth of Metal Nanoparticles on Nanowire Substrates

The production of nickel and platinum nanoparticles on silica nanowire substrates using plasma-enhanced chemical vapor deposition has been investigated. Determination of particle size and particle size distribution was done using transmission electron microscopy (TEM). Ni nanoparticle diameters were found to be between 2 and 6 nm, with particle size increasing as the substrate temperature increased from 573 to 873 K. The size of Ni nanoparticles was found to be dependent on the chamber pressure during growth. The results indicate a competition between pressure-related diffusion within the vapor and dissociation of the precursor. Pt nanoparticle diameters were consistently found to be 2.5–3.0 nm at all deposition conditions. Insufficient thermal energy within the studied range results in a minimal contribution from surface diffusion, the primary mechanism for nanoparticle growth.     

基于粒子谱分布的无线紫外光通信散射传输特性研究

在非直视无线紫外光通信中,利用大气中的粒子对紫外光进行散射作用来传递信息,非直视紫外光通信在近距离隐蔽通信中有广阔的应用前景.雾霾粒子属于气溶胶范畴,由空气中的灰尘、硫化物、有机碳氢化合物等粒子组成.雾霾粒子的尺度、浓度、形状等因素均会对无线紫外光散射通信的传输特性产生较大的影响.首先,基于蒙特卡罗方法建立了非直视紫外...