FAE爆炸抛撒后云雾液滴尺寸的测量

用光学方法测量悬浮于气相或液相介质中的微小颗粒特性已被广泛地采用。R．A．Dobbins于1963年用简单的方法来单独测定喷雾颗粒平均直径。20世纪70年代采用激光器和自动数据处理系统。液体轴对称抛撒是非定常过程，即在固定位置观察到的液体颗粒尺寸随时间的变化而变化。光线通过含有微粒的介质时会发生光的散射现象，Dobbins根据颗粒散射原理，把满足上限分布函数(ULDF）且直径为几十到几百微米的颗粒散射作为衍射散射处理。     

沙尘天气下大气能见度对激光光强的影响

基于米氏理论,分别研究了不同波长的激光信号在沙尘天气中发生单次散射和多次散射时光强与能见度间的变化关系.推导出发生单次散射时光强与能见度间的解析表达式,同时采用蒙特卡洛方法分析了发生多次散射时光强与能见度间的关系,并与单次散射时的结果进行对比.结果表明:在激光信号波长固定时,接收光强会随着沙尘能见度的增大而增加,并趋于稳定值;在能见度固定时,接收光强会随着激光信号波长的增大而减小;随着传输距离的增加,多次散射的影响会越来越明显.     

沙尘天气下激光信号的传输特性

以小角度近似为条件,利用逐级递归的方法推导了激光信号在沙尘天气下的辐射传输方程,得到了多次散射下的光强分布函数,以及波长和不对称因子对光强的影响。同时,通过比较不同散射相位函数及沙尘粒子的散射特性,采用了修正的TTHG(Two Term Henyey-Greenstein)散射相位函数,更加全面地反映了沙粒散射后光强的变化规律。研究结果表明,随着光学厚度的增加,散射光强呈现出先增大后减小的趋势,且多次散射的比重相比于单次散射而言逐渐增大。当散射次数超过3次以上时,接收光强的变化可以忽略不计。相对于Mie理论下的结果而言,采用小角度近似理论,从辐射传输的角度分析沙粒的散射特性误差更小,实现了准确描述沙尘天气下激光信号传输特性的目的。     

光全散射法测量微粒尺寸分布的研究

本文从光全散射法的基本原理出发,提出了测量微粒尺寸分布的独立道模式光全散射测量法和非独立模式光全散射测量法,解决了以往光全散射法只能测量微粒的平均直径,不能给出尺寸分布,并且测量范围小,测量结果有多值性的缺陷,独立模式光全散射测量法还能用于测量多峰分布微粒的尺寸分布,数值计算和实验研究表明用本文方法,测量结果准确,可靠。     

液滴撞击加热壁面传热实验研究

本文采用高速摄像仪对水滴和乙醇液滴撞击加热壁面后的蒸发过程进行了实验观测, 分析了液滴撞击加热壁面后的蒸发特性参数. 实验中, 两种液体初始温度均为20 ℃, 不锈钢壁面初始温度范围为68-126℃. 水滴初始直径为2.07 mm, 撞击壁面时Weber 数为2-44; 乙醇液滴初始直径为1.64 mm, Weber数为3-88. 结果表明, 液滴受到重力、表面张力及流动性的影响, 在蒸发过程的大部分时间内, 水滴高度持续降低而接触直径几乎不变; 蒸发后期, 液滴发生回缩, 水滴的接触直径、高度和接触角出现振荡现象. 乙醇液滴的接触角随时间的增加呈现先减小随后保持不变的趋势, 而接触直径和高度则持续减小, 直到液滴完全蒸发. 液滴蒸发总时长与液体物性和壁面温度有关, 随壁面温度的升高而减小, 与液滴撞击壁面时的Weber 数无关. 同时, 随着壁面温度的升高, 液滴显热部分占总换热量的比重增大, 显热部分能量不可忽略, 本文实验条件下得到水滴的平均热流密度为0.014-0.110 W·mm^-2.     

气泡雾化喷嘴喷雾平均直径在下游流场中的分布

文利用激光衍射粒度仪对气泡雾化喷嘴下游流场进行了实验研究,主要分析了雾化颗粒直径随径向和轴向距离变化的趋势．由于喷嘴出口处气液两相流型和颗粒自身重量的影响,液雾颗粒沿径向呈现非轴对称分布;而液雾颗粒直径随着轴向距离的增加呈现先减小、后增大的趋势,颗粒直径的减小是大量气泡爆炸的结果,而后的增加则是由于颗粒之间的相互粘结造成的。     

弱散射屏的像面散斑自相关函数特性的实验研究

在对随机弱散射屏进行表面参数的原子力显微镜测量和建立了门积分取样平均的随机光强自相关函数测量系统的基础上,对弱散射屏在严格像面和离焦像面上产生的散斑自相关函数进行了测量。发现在严格像面上,散斑平均颗粒的大小随表面粗糙度增加而减小,且光强自相关函数次极大的相关间隔宽度随粗糙度增加而减小;而次极大的超伏随粗糙度的增大而增大;在离焦像面上,离焦量的增加使光强的自相关函数下降变得平滑,并使极小值点和次极大点变得不明显或者消失。     

基于一阶彩虹区域高斯光散射的液滴测量

为实现雾化过程中局域内单液滴的测量,采用德拜级数展开研究了高斯光照射下球形液滴一阶彩虹区域的散射光强分布,以及高斯光束腰大小对光强分布峰值角度的影响.根据德拜级数展开计算的散射光强分布反演液滴的折射率和粒径,证明了根据高斯光的彩虹散射反演液滴信息的可行性.基于广义洛伦兹-米氏理论计算一阶彩虹区域的总光强分布,根据总光强分布反演液滴折射率和粒径,讨论了高斯光束位置对反演液滴信息的影响.对于半径在200~1 000μm区间的液滴,高斯光束位于中心入射时,反演折射率的误差小于2.38×10-4,粒径的相对误差在-3.31%~3.31%之间.与采用平行光彩虹技术相比,采用高斯光束为入射光可以得到较高的光能聚集区,较好地定义测量区大小,既可以有效避免多个液滴同时出现在测量区的情况、减小颗粒之间复散射的影响,又可以提高信号强度.     

水平管油水分散流液滴粒径及其分布规律研究

油水两相分散流是油水混输管道常见的流型之一,液滴是油水分散流的主要特征,液滴在油水两相管路中受到湍流惯性力、剪切力、界面张力、黏性力等多种力的作用而发生聚结和破裂,从而形成不同的液滴粒径及其分布。本研究采用高速摄像和显微照相两种方法研究了水平管中油水分散流的液滴粒径随混合流量、温度和含油率等参数的变化规律,并利用三种概率分布函数研究了液滴粒径的分布特性。研究结果表明:分散相液滴的Sauter平均直径随混合流量的增加而逐渐减小、随温度升高而逐渐增大、随含油率的增大而增大;液滴粒径的分布规律与Log-Normal和Frechet概率分布函数符合较好。     

涡旋光束形成的散斑场光强和相位的分布特性

通过对不同拓扑荷的涡旋光束经随机表面散射后在衍射区形成的横向和纵向光强分布的模拟,发现散斑颗粒的横向和纵向的平均尺寸比用高斯光束照明随机表面产生的散斑颗粒平均尺寸小很多,并且随着涡旋光束拓扑荷和光斑半径的增大而减小,同时散斑场相位涡旋的密度随着涡旋光束拓扑荷和光斑半径的增大而增大。利用这种方法可以方便地选择不同拓扑荷和光斑半径的涡旋光束照射随机表面,得到合适的散斑颗粒来捕获更小的微粒。这种结果还可以用来降低散斑噪声。     

Structure of Liquid‐Sheet Sprays

Spray characteristics and their spatial distribution have been investigated experimentally for sprays generated by the breakup of thin liquid sheets in co‐flowing air streams. The spray characteristics such as droplet mean and fluctuation velocity and Sauter mean diameter have been measured by using phase Doppler anemometry under various liquid and air flow conditions at the nozzle exit. The results show that at a given spray cross section the droplet axial mean velocity has a maximum value at the spray center, and decreases towards the edge of the spray; whereas the Sauter mean diameter has a minimum value at the center and increases monotonically towards the spray periphery. Data analysis indicates that sufficiently downstream of the nozzle exit the droplet mean velocity attains a jet‐like self‐similar distribution in the transverse direction, and such universal distribution is also observed for the turbulent fluctuation velocity and turbulent intensity, although it is achieved further downstream compared to the mean velocity profile. The Sauter mean diameter at the spray center has a complex variation in the downstream direction due to secondary atomization at high air velocity near the nozzle exit and droplet entrainment, migration and possible coalescence farther downstream.     

燃油粒度对两相PDE爆震波速的影响

两相爆震燃烧的研究近来取得了较大的进步,但是仍有很多问题需要解决,诸如燃油的喷射、雾化和蒸发,燃油和氧化剂的混合,两相可爆混合物的短距离起爆等等．本文利用激光喷雾粒度分析仪分别就直射喷嘴与气动喷嘴研究了汽油的雾化情况,随着汽油流量的增加,两种喷嘴的雾化变化趋势相反．结合汽油、空气PDE模型机多循环爆震试验,发现汽油的粒度对模型机的爆震波速有较大的影响,粒度减小,波速增大,同时波速具有循环效应．     

Dynamic Light Scattering Measurement of Nanometer Particles in Liquids

Dynamic light scattering (DLS) techniques for studying sizes and shapes of nanoparticles in liquids are reviewed. In photon correlation spectroscopy (PCS), the time fluctuations in the intensity of light scattered by the particle dispersion are monitored. For dilute dispersions of spherical nanoparticles, the decay rate of the time autocorrelation function of these intensity fluctuations is used to directly measure the particle translational diffusion coefficient, which is in turn related to the particle hydrodynamic radius. For a spherical particle, the hydrodynamic radius is essentially the same as the geometric particle radius (including any possible solvation layers). PCS is one of the most commonly used methods for measuring radii of submicron size particles in liquid dispersions. Depolarized Fabry-Perot interferometry (FPI) is a less common dynamic light scattering technique that is applicable to optically anisotropic nanoparticles. In FPI the frequency broadening of laser light scattered by the particles is analyzed. This broadening is proportional to the particle rotational diffusion coefficient, which is in turn related to the particle dimensions. The translational diffusion coefficient measured by PCS and the rotational diffusion coefficient measured by depolarized FPI may be combined to obtain the dimensions of non-spherical particles. DLS studies of liquid dispersions of nanometer-sized oligonucleotides in a water-based buffer are used as examples.     

Calculation method for particle mean diameter and particle size distribution function under dependent model algorithm

In total light scattering particle sizing technique, the relationship among Sauter mean diameter D32, mean extinction efficiency Q, and particle size distribution function is studied in order to inverse the mean diameter and particle size distribution simply. We propose a method which utilizes the mean extinction efficiency ratio at only two selected wavelengths to solve D32 and then to inverse the particle size distribution associated with (Q) and D32. Numerical simulation results show that the particle size distribution is inversed accurately with this method, and the number of wavelengths used is reduced to the greatest extent in the measurement range. The calculation method has the advantages of simplicity and rapidness.     

液滴微粒直径分布的激光散射法测量

本文利用氦氖激光器为光源在自行设计的光散射实验装置上对球形微粒群进行了粒径平均直径及直径分布的理论研究和测量.实验结果表明,本实验装置具有测量精度高、适用范围广和测量粒径范围宽等特点.     

Particle Breakup in Shock Waves Studies by single Particle Light Scattering

The breakup of suspended, agglomerated submicron particles was studied by exposing the aerosol to weak shock waves of varying strength under conditions 400 ms^?1?v?880 ms^?1. A newly developed laser light-scattering diagnostic employing a top hat laser profile was used to size the particles passing through a very small scattering volume. By Comparing the optically measured particle size in front of and behind shock waves, the breakup of agglomerated particles could be clearly identified. The experiments indicate that the aerodynamic forces behind an incident shock overcome the particle binding force resulting in disintegration of the submicron agglomerates. The results are presented in form of a modified Weber number.     

用全固态激光器和一维CCD测定微粒粒径

建立了一套利用线阵CCD探测散射光强从而测定粒径的实验装置.该装置采用线阵CCD取代传统的同心环探测器,并采用一台小尺寸全固态绿光激光器取代传统的He-Ne激光器.理论上采用全Mie氏散射理论,自行编写了实验数据的计算机拟合程序,可以由实验测得的散射光强角分布反演求出粒径分布信息.对粒径分别为4.91 μm和9.88 μm的聚苯乙烯小球均取得了良好的粒径测量结果.该装置被证实可用于测定的粒径范围为0.7 μm～44.0 μm.     

超声速气流中液体横向射流雾化过程数值模拟

为了更加深入了解超燃冲压发动机燃烧室中的燃料雾化机理,对来流Mach数为1.94的超声速气流中液体横向射流的雾化过程进行了数值模拟研究.计算采用Euler-Lagrange方法,液滴二次破碎模型采用K-H/R-T模型.计算结果表明:考虑液滴二次破碎时,采用雾化锥模型获得的射流穿透深度以及液滴速度分布与实验结果符合得很好...     

光源的偏振态对动态光散射颗粒测量结果的影响

研究了在动态光散射纳米颗粒测量中,光源的偏振态对测量结果的影响。采用了粒径为100nm、体积浓度为0.5%的标准颗粒作为样品,使He-Ne激光通过起偏器得到0°～180°方向的偏振光,测量了散射光强、偏振度和粒径测量值的变化,计算了相应的粒径均值偏差和标准差,并将这一结果与无偏振He-Ne激光入射进行了比较。结果表明,当入射光为线偏振光时,偏振方向垂直于散射面时测量效果最好;另一方面,由于颗粒系散射迭加造成的散射光偏振度降低,使线偏振光源与无偏振光源产生的散射光偏振度无明显差别,证明在测量中可以使用无偏振He-Ne激光代替。     

Determination of particle size in multiphase blends by different methods

Different methods for characterizing the morphology of multiphase blends were applied to a blend of thermoplastic polyurethane with 20 wt% polypropylene as the dispersed phase. Optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and light scattering were compared. The microscopy methods were evaluated with respect to their suitability for quantitative image analysis for determination of the particle size distribution. Comparison of the particle size distributions revealed that the dependence of the measured particle size on the method of preparation and technique was not very pronounced. The main difference resulted from cutting the particles outside their maximum diameter. The measured particle sizes determined with methods that analyze the whole particles, such as SEM on separated particles and laser light scattering, are larger than those measured on cut specimens. The factor 4/π valid in monodisperse systems for the ratio between the real particle size and that measured on sections was found also to be applicable to this polydisperse blend system. Although light micros-copy requires the least preparation efforts, it is a reliable method for this blend system.