显微粒子图像测速技术——微流场可视化测速技术及应用综述

目前,随着微流动器件的应用领域更加广泛,包括化学、生命科学、芯片实验室及微加工制造(Micro electro mechanicalsystems,MEMS)等相关领域,流体在微流动器件内部的流动行为成为重要的研究内容。微尺度、低雷诺数流动的表面力作用相对增强,微尺度流动行为与宏观尺度有显著不同,目前许多复杂的微尺度流动现象还无法给出合理的解释。显微粒子图像测速技术(Micro-scale particle image velocimetry,Micro-PIV)是一种整场、瞬态、定量的微流场可视化技术,目前已达到相当高的分辨率(0.1μm),成为一种重要的微流动研究手段,引起广泛的研究关注。综述Micro-PIV技术在基本理论、关键技术、三维测速等方面的最新研究进展,并重点介绍Micro-PIV技术在近壁面流动、电渗流、微混合、生物流体、微液滴与气泡等研究中的应用进展,最后对此项技术的发展做展望。     

粒子图像测速(PIV)技术的发展

在流场显示测量技术中，粒子图像测速(PIV)技术占有相当重要的地位，本文重点介绍了PIV的测试原理及应用要求，并以TSI公司开发的PIV系统为例对DPIV系统的构成作了概括，同时指出了PIV技术的未来发展方向。     

显微粒子图像测速计算方法

粒子图像计算方法是显微粒子图像测速技术中重要的研究内容,图像计算精度是决定流体测速结果不确定度的重要因素.在分析单幅双曝光自相关算法和单幅单曝光互相关算法的基础上,将统计互相关算法和平均算法相结合,提出平均统计互相关算法.在不同诊断窗口大小下对粒子图像的计算结果显示,统计互相关算法的精度高于其他两种相关算法.分析了诊断窗口大小对计算精度的影响,给出计算参数的选择方法,并给出利用平均统计互相关算法计算微沟道中粒子图像的结果.     

微流体芯片中流体温度软测试技术研究

在微流体芯片的众多应用研究领域中,如微反应器、PCR扩增、微流体驱动和控制等,微流体芯片中的流体温度和热量控制是一个非常关键的因素,为此国内外学者在微流体芯片温度测试和热控制方面进行了大量的研究.不管采用何种加热方式,加热板或者是芯片本身,都不能代表微流体芯片中流体本身的温度.本文提出一种微流体芯片中流体温度软测试技术,核心是利用比较容易测量的辅助变量(流体周围的芯片温度)来推断不可测的流体温度变量.通过构造辅助变量与流体温度变量数学映射关系,实现对流体温度的在线估计.根据微流体芯片中微流体传热机理分析,建立了微流体温度软测试数学模型,并用模拟试验验证了模型的正确性.     

微流体机械全流场数字粒子图像测速技术

提出了一种针对MEMS技术制造的微流体机械全流场数字粒子图像测速技术,通过添加荧光显微装置,改进照明光源以及示踪粒子的选型等解决微观检测的关键问题。针对微流体特征尺度小、精度要求高的特点,讨论了基于互相关原理的速度矢量识别算法。并就微流体检测中引起主要误差的示踪粒子布朗运动效应提出了全体平均图像处理方法。     

微纳米力学测试系统的研制

采用闭环控制微纳压电位移驱动器为核心加载装置,以压电式微力传感器作为测量装置,集成显微光学数字视频监测系统,并编写完整的测量、控制与标定算法软件,研制量程0.1m N-500m N的全自动微纳米力学测试系统。该系统具有被测样品与实验探针的自动定位、可编程自动加载与显微实时监测与记录功能,能够满足小至微米级样品的实验要求,填补现有微纳测试仪器因量程过小或功能不足等问题所导致的空白,预期可应用于微纳机电、微纳米材料、生物医学工程等领域。     

微通道换热器试验测试系统研究

搭建了一套测试微通道性能参数的循环换热试验系统,介绍了组成该系统的微通道换热器、模拟芯片、微型泵、恒温装置以及控制测量等部件.以水为介质,对三种不同结构型式微通道换热器的传热及流动性能进行了试验研究,测量了进出微通道换热器的冷却液流量、温度和压差以及模拟芯片表面多个测点的温度等参数,获得了微通道换热器内的流动阻力和传热特性.     

MEMS动态测试系统中频闪驱动电路的实现

在MEMS动态测试过程中,由于MEMS器件的运动频率都比较高,如何获得高速运动的MEMS器件的清晰图像,是MEMS动态特征提取与分析的前提.本文基于机器微视觉的MEMS动态测试系统,设计了一套频闪驱动电路,用于采集高速运动的MEMS器件的清晰图像.从而为后续MEMS器件动态特征的提取和分析做充分的准备.     

火炮稳定精度图像测试系统

为了高精度测试火炮稳定精度,建立了基于CCD与标准靶板的图像测试系统。介绍了测试系统的组成结构与工作原理,研究了系统采用的图像预处理、模板匹配、靶标十字中心定位和系统标定等关键算法。为消除分划板十字线对靶板十字识别的干扰,采用了开关中值滤波算法;在选取灰度变换算法提高图像对比度的基础上,分析选取了模板制作与匹配算法;然后,介绍了靶板十字中心的像素级和亚像素级定位;最后,引入基于主动视觉的标定方法确定了系统的像素角分辨率。试验结果表明:提出的系统测试精度优于0.07 mil,满足实际测试需要,实现了带有稳炮功能的现代火炮系统的稳定精度靶场测量。     

基于机器微视觉的MEMS平面微运动测试技术

随着微电子机械系统(MEMS)研究的深入和产业化的需求,检测技术在MEMS中的重要性越来越大。基于机器微视觉原理组建MEMS动态测试系统,在此系统之上,提出模糊图像合成技术对MEMS器件的平面微运动特性如谐振器的运动幅度、谐振频率等重要参数进行了测试,给出了测量结果,并对测试结果进行了分析和讨论。     

二值化粒子成象流速测量系统研究

本文提出了数字ＰＩＶ技术中采取二值化数值采样思想，并对二值化粒子成象流速测量系统的实现及其程控光源、二值化采样、图象处理各部分工作原理作了介绍。论述了在ＣＣＤ工作原理基础上提高系统测速上限的方法。论文还介绍了利用该系统对转盘速度径向分布的测量结果及对方管内圆柱扰流流场的测量结果，并给出了流场速度矢量分布图。     

DPTV算法的精度分析

数字化粒子迹线测速技术（DPTV）是根据曝光时间内示踪粒子形成的图像来确定流体瞬时速度的。PTV系统的优势是对硬件要求低、计算快、方便操作。但是，粒子迹线测速方法存在速度方向模糊的问题，且在曝光时间内，示踪粒子可能由光带内运动到光带外，这必然导致测速的不准确。该文提出了一种能消除方向模糊性的方法，并且分析了造成DPTV测速出现错误向量的原因和错误向量出现的概率。     

微流场可视化测速技术及其应用

介绍了一种针对微观流场检测数字粒子图像测速技术，通过添加荧光显微装置，改进激光入射与照明方式及聚焦平面控制，解决了微观检测的关键问题。对微流体器件中几种典型微管道进行了理论与试验研究，并定量对比与分析了仿真与试验结果，结果显示Micro—PIV是适合于微米级流场检测的有效试验手段。     

Application of the Method of Particle Image Velocimetry for Analyzing Turbulent Flows with a Periodic Component

The foundations of the field method for measuring the flow velocities—the particle image velocimetry (PIV) method—are presented. An approach is described that ensures measurements of conventionally averaged characteristics in flows with pronounced periodicity. Using the high-resolution PIV and conditional averaging methods, detailed measurements of the velocity fields in an axisymmetrical impact jet have been performed for the first time. The flow characteristics are analyzed using a triple decomposition of fluctuating quantities.     

Particle Image Velocimetry Measurement of the Flow Field in the Play of the Drilling Pump Valve

The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry(PIV) technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics(CFD) simulations.     

离心泵偏置短叶片叶轮内部流动的粒子图像速度测量

对三副短叶片不同偏置的低比转数复合叶轮离心泵,应用粒子图像速度仪分别测试大流量、设计流量和小流量三种工况下长短叶片叶轮同一叶槽内的瞬时流场.分析叶槽内相对速度矢量、速度等值线的特征,揭示短叶片不同偏置时的速度分布规律.研究三副长短叶片复合叶轮出口处径向速度、切向速度、相对速度和相对液流角沿圆周的分布,测得与三副叶轮相对应的泵外特性曲线.测量结果表明,分流短叶片不同偏置对叶槽内流场的影响差异明显,当短叶片进口相对出口向压力面偏转时,叶轮出口相对速度分布很不均匀,短叶片工作面出口存在较大的低速区;与之相反,当短叶片进口相对出口向吸力面偏转时,叶轮出口速度分布较均匀,并且泵的扬程与流量曲线明显右移,大流量时,效率显著提高.     

基于PIV的泥泵叶轮内颗粒相对速度场的研究

泥泵是挖泥船的核心设备,泥泵性能与叶轮内泥砂颗粒的运动密切相关。本文采用PIV(粒子图像测速)测量技术,分别对中砂(粒径0.2~0.4 mm)和粗砂(粒径0.8~1 mm)在叶轮内的运动速度进行了测量。研究表明:中砂颗粒沿流道的相对速度变化趋势与液相相似,均在流道前半段出现高速区,在后半段出现低速区,且中砂颗粒的相对速度值均高于液相;而粗砂颗粒在叶轮流道内相对速度值变化较小,在流道前半段低于液相,在后半段与液相相差不大。     

Methods for Digital Particle Image Sizing (DPIS): Comparisons and improvements

This paper explores the accuracy of particle image sizing using direct processing of digitally recorded images. Traditional methods for particle image sizing were considered and, four new algorithms were developed to deliver improved accuracy and robustness. Statistical error analysis was performed using Monte Carlo simulations in order to quantify the dependence of these methods on noise, discretization, and particle size distribution. The performance of these methods were compared against Phase Doppler Analyzer measurements of spray atomization.We introduce a novel two-dimensional four-point Gaussian estimator and an alternative Gaussian estimator based on a local least squares (LLS) fit. These methods were further advanced to account for pixel discretization effects using integral formulations (continuous methods). All new methods were compared against conventional pixel counting and the established three-point Gaussian estimator. The new methods significantly reduced the total error in the diameter estimation compared to the three-point Gaussian estimator and pixel counting. The least squares Gaussian estimator and its continuous version demonstrated almost identical results and superior performance for diameters over 4 pixels. For smaller diameters, the continuous four-point Gaussian estimator delivered the highest accuracy. For uniform particle size distribution between 2–14 pixels image diameter, the least squares estimators delivered error less than 5% with respect to the true diameter for 80% of the particles. The remaining methods demonstrated error of 5% (or better) for less than 60% of the particles. Validation in an experiment of high-pressure spray atomization showed that the Gaussian local least squares methods and the continuous four-point method delivered similar particle size distribution compared to PDA. The particle mean diameter estimated by the two methods differed only by 3% and 6% respectively with respect to the PDA measurements.The novel particle image sizing schemes developed here can deliver accurate, robust, and computationally efficient apparent diameter measurement, thus providing a viable, simple and inexpensive solution for performing sizing on conventional particle image velocimetry images. This capability enables simultaneous measurements of both velocity and particle size for a wide range of multi-phase flows.