Capacitance-based concentration measurement for gas-particle system with low particles loading

A parallel-plate capacitance-based sensor configuration which can be used to measure low mass concentrations down to a few tens of g/m³ for gas-particle systems and to study the influence of the particle characteristics such as particle size, packing or agglomeration on the effective permittivity of the mixture was developed. In this sensor a two channel symmetric structure and an AC bridge circuit were adopted to minimise the influence from the surrounding factors such as temperature, pressure and humidity. The inner diameter of the flow pipeline is 18 mm, the dimension of the capacitance plate is 100 mm×50 mm and the distance of the two plates is 10 mm. To measure the concentration of particles an in situ two-step measurement was proposed, i.e. zero point and loading measurements. Emphasis was made on estimation of the static and dynamic performance of the capacitance sensor and configuration.The baseline drift of the sensor and the influence of surrounding factors were studied. Dynamic experiments show a relative measurement error of 8% in the range from 10 to 300 g/m³. Static experiments for locally packed particle-gas systems show that the response of the sensor depends not only on particle material but also on particle size.     

阵列式静电-电容传感器灵敏度特性研究

结合静电和电容传感技术各自的特点,提出了阵列式静电-电容传感器用于气固两相流中固相颗粒的局部速度、局部浓度以及局部流量测量。利用静电极片阵列与电容极片阵列获取管道内颗粒的速度分布与浓度分布,进而计算出颗粒的局部流量。该阵列式传感器参数测量的准确性直接取决于它的空间灵敏度分布特性。对静电极片阵列和电容极片阵列的灵敏度特性进行了研究。首先,建立了静电极片阵列的三维静电场模型,通过有限元法分析静电极片阵列的结构参数(电极长度、电极覆盖角等)对传感器灵敏度特性的影响;然后根据电磁场理论建立电容极片阵列的数学模型,并对其进行数值计算,研究管道厚度、管道介电常数、电极覆盖角等参数对传感器灵敏度特性的影响;最后搭建了传动带装置进行了实验研究,实验结果证实了模拟结果的准确性,为阵列式静电-电容传感器的优化设计提供理论依据。     

柴油发动机超细颗粒物数量检测方法研究进展

柴油机的颗粒物排放是城市大气超细颗粒物的主要来源,对环境质量和人体健康有严重的负面影响。近年来,排放法规对颗粒物排放的控制愈加严格,并对颗粒数量测量仪器的性能提出了更高的要求。总结了5种颗粒数量测量仪器的测量原理和特点,在特定测量需求和场合下对这些设备的性能进行了对比并针对下一阶段排放法规的测量需求,分析了以上测量设备的适用性。结果表明,冷凝颗粒计数器对粒径>10 nm颗粒具有更快的响应速度,能够满足未来法规中对城市RDE测试循环的需求。然而,冷凝颗粒计数器无法测量粒径分布,不适用于针对10～23 nm颗粒控制技术的研发。但发动机排气粒度仪可给出粒径低至5.6 nm颗粒的粒径分布,可为冷凝颗粒计数器的检测结果提供补充信息。     

液固两相介质多频超声粒径分布测量

液固两相流动广泛存在于工业过程中,其粒径分布信息在线测量对生产优化与控制十分重要。超声法作为无扰动式多相流动参数测量方法,其衰减特性与固相颗粒粒径、体积分数等密切相关,可用于实现粒径分布在线测量。本文搭建液固两相介质超声衰减实验装置,装置采用石英砂作为固相颗粒,自来水为液相,利用线性调频超声信号激励研究液固两相介质的超声衰减特性。实验结果表明,随着激励频率和固相体积分数的升高,超声衰减系数逐渐增加,采用Twomey及遗传算法等对液固两相介质粒径分布进行反演,测试结果与马尔文激光粒度分析仪的粒径分布结果相比,相关系数为0.918。     

金属颗粒的电容式速度测量方法研究

针对金属材料在静电场中呈现出的特殊性,设计了一种用于检测管道中金属颗粒速度的电容式传感器.首先,基于多电极理论建立了电容传感器测量金属物质的数学模型,在此基础上,使用COMSOL Multiphysics有限元分析工具建立了传感器三维仿真模型,并对其空间灵敏度分布特性进行了分析.然后,基于该传感器的空间滤波效应对金属颗...     

求解粒子群粒度分布的改进Projection算法

针对在激光粒度分布反演中由于迭代算法的迭代步长选取不当致使反演结果存在严重展宽和拖尾的问题,提出一种调整迭代步长的方法应用于Projection算法来提高测量精度。该方法首先基于测距相似度原理得到光能分布列向量与光能系数矩阵行向量之间的相似度曲线,经滤波和归一化处理后得到被测粒子群的预测粒度分布;然后根据预测粒度分布结果确定迭代步长的大小。使用本文提出的改进Projection算法测量国家标准物质GWB(E)120046的D50误差为-0.6%、D10误差为-1.1%、D90误差为-0.6%,测量GWB(E)120041与GWB(E)120049混合标准物质的光能对数误差为2.167。测量结果表明,该算法可有效地提高算法的抗噪声能力、测量精度和分辨率。     

应用探针式电容传感器检测发动机润滑油品质的研究

应用探针式电容传感器测量润滑油中固体颗粒含量的原理,是根据固、液体混合物在电容器两极板之间介质的介电常数变化而使电容发生变化。应用该原理设计出了一套润滑油油品监测系统,简称为YPT系统。应用该系统,对发动机润滑油中的铁、硅固体微粒含量变化与电容变化的相互关系进行了初步探讨,并建立起来了一种新的润滑油品质YPT评价标准。这个新的评定标准,为确定发动机润滑油的更换周期及预测发动机的使用寿命等方面的研究,提供了一种比较简便实用的科学依据。     

电容传感器在沥青含量测量中的应用

在分析了沥青混合料的特性及沥青路面结构的基础上，根据筑路现场的实际工况，提出了利用一对柱面形极板结构的电容传感器测量沥青含量的设计方案，并研制了智能测量系统。通过对大量实验测量数据的分析和计算，一方面确定了沥青混合料的等效介电常数与沥青含量之间的一一对应关系，另一方面使传感器结构得到进一步优化、完善。即将敏感元件电容和步进电机及驱动系统有机的结合在一起构成了旋转式电容传感器，实现了沥青含量的全自动测量，不仅为沥青含量的测定提供了一种新方法，而且经实验证明该方法简便、可行。     

基于介质层耦合的柔性触觉传感器空间分辨率补偿方法研究

传统柔性压力传感器采用离散电容结构,传感器空间分辨率受到最小离散单元的限制。对于作用面积较小的外力接触,现有柔性传感器仅能通过减小离散单元面积确定接触位置,而离散单元过小则会造成制作困难、接线复杂、成本升高。为解决微小接触面积下空间分辨率偏低问题,提出了一种基于整体介质层耦合结构柔性传感器,通过建立传感器接触及扩散电容单元的数学模型,能够在不降低电极面积的情况下,通过接触及扩散电容对接触位置进行准确判断,显著提升柔性压力传感器的空间分辨率。仿真及试验结果表明:所设计的基于耦合介质层8×8阵列传感器的受力模型获得了0.2 mm×0.2 mm的空间分辨率,在较低的制作成本以及传感器尺寸稍大的前提下,大大提高了阵列传感器的空间分辨率。     

基于LS-SVM的油气两相流空隙率测量方法的研究

利用12电极电容层析成像系统电容传感器获取的66个电容测量值,基于最小二乘支持向量机（LS-SVM）算法,提出了两相流空隙率在线测量的新方法。该方法用LS-SVM来建立空隙率测量模型。在实际测量时,首先归一化ECT获取的电容测量值,然后将归一化电容值输入已经建立的空隙率模型即可计算出空隙率。实验结果表明：该方法是有效的,避免了复杂耗时的图像重建过程,测量误差在6%以内,测量时间小于0.08 s。     

基于固体颗粒尺寸分布的微孔滤膜堵塞机理分析

滤膜堵塞法是一种半定量的油液污染度检测方法,研究固体颗粒尺寸分布与滤膜堵塞机理的关系有助于该检测方法的定量化。利用AC细粉尘及煤粉配制了8种不同尺寸分布的悬浮溶液,选择了10 μm、15 μm两种不同尺寸的微孔滤膜,对其堵塞机理与溶液中固体颗粒尺寸分布的关系进行试验研究。基于膜孔尺寸将颗粒划分为可通过颗粒、敏感颗粒、架桥颗粒及易挡孔颗粒,将溶液恒压下通过微孔滤膜的流量衰减曲线与经典堵塞模型的堵塞指数相结合,分析不同类型颗粒在膜孔堵塞中的作用以及不同颗粒尺寸分布对应的滤膜堵塞机理。分析结果表明,微孔滤膜堵塞机理与溶液尺寸分布规律相对应,与膜孔尺寸的选择无关;溶液中的敏感颗粒越多,对滤膜的初始堵塞会越严重,越易形成滤饼;对于可通过小颗粒较多、敏感颗粒和架桥颗粒适量、易挡孔颗粒较少这种液压系统中常见的颗粒尺寸分布规律,微孔滤膜的堵塞以标准堵塞-滤饼过滤为主要机理。首次从颗粒尺寸分布的角度分析微米级滤膜堵塞机理,分析结果有助于建立滤膜通量与固体污染颗粒尺寸分布之间的关系,从而提高滤膜堵塞法的油液污染度检测精度。     

Characterization of gas-liquid two phase flows using dielectric Sensors

Two phase flow regime identification and void fraction measurement is an area of considerable interest because of its wide applications in process industries. The principle involved in dielectric measurement is that the two phase flow regime is characterized by the changes in effective permittivity of the two phase fluid mixture. In the present work, a pair of parallel copper electrodes on the two sides of a glass tube acts as a dielectric sensor. As the void fraction in the glass tube changes, the effective permittivity of the medium changes. This causes a variation in the capacitance value across the electrodes. A standard IC, Oscillator 555 is employed as a tool to generate a rectangular wave. The variation in dielectric constant is analyzed based on the change in time period of the trough (T₀) of the rectangular wave that is recorded online by a data acquisition system. Experiments were performed in a 4.7 mm diameter tube with air-water, air-palmolein oil two phase fluids to study the variation in dielectric constant which is indicated as a change in time period of trough. The effect of conductivity of water on the capacitance variation is examined with water having Total dissolved solids (TDS) which is a measure of movable ions in the range 10-4000 ppm (16 µS/cm–6.3 mS/cm). The novelty in the present work is the determination of changes in capacitance value based on the change in time of trough of the rectangular wave. The technique does not require amplification or a filtering circuit, thereby leading to a precise identification of two phase flow regime.     

近壁面超声空化微射流对微细颗粒的破碎作用

针对微细粉体“团聚”导致粉磨极限的问题,在液相环境下利用超声的分散和空化冲击作用,开展了近壁面超声空化微射流对微细颗粒破碎作用的研究。通过理论计算空化微射流冲击微细颗粒破碎的有效作用范围,从空化泡溃灭速度的角度分析了超声频率、声压幅值、介质尺寸等主要参数对微射流强度的影响;结合物料质量浓度、介质尺寸、介质面积和功率等影响因素的微细颗粒超声空化破碎正交试验,并利用SEM观测粉体形貌,分析了颗粒中位粒径D50、10%体积累积粒径D10和比表面积（SSA）等分布特性。参数组合优化后获得了粒径小于800目的微细颗粒,破碎率高达79.35%;粒径大于10 000目的极细颗粒产率高达12.84%。从提高微细颗粒破碎率的角度,发现介质面积是主要影响因素,功率次之,其次为介质尺寸和物料质量浓度。试验结果与理论研究成果基本一致,表明优化超声空化微射流参数与增加介质壁面面积等方法可有效提高微细颗粒的破碎率。     

非闭合电极电容层析成像传感器在冻土测试中的应用

为了实现电容层析成像技术对冻土冻结冰峰面的在线、非侵入测试,研制出了满足冻土测试要求的非闭合电极电容层析成像传感器,并对该种传感器的电容分布特性进行了实测;确定出了适合冻土测试的的高、低介电常数的标定物质;搭建了冻土一维冻结实验系统.对含水量8%的湿土样冻结过程的冰峰面迁移进行了电容层析成像测试,并利用IMNSNOF图像重建算法重建出了冻结过程各时刻的冻结截面物质分布图像,由图像可确定出冻土中已冻土、未冻区以及冰峰面的位置.电容层析成像测试结果与温度测试结果相吻合.     

Capacitance wire-mesh sensor applied for the visualization of three-phase gas–liquid–liquid flows

This short communication describes the application of a capacitance wire-mesh sensor for the investigation of a gas–liquid–liquid three-phase flow in a laboratory setup. Experiments with air, silicone oil and water are performed first in static and second in dynamic flow conditions. The capacitance mesh sensor is capable of generating images of the cross-sectional distribution of relative permittivity values, which in turn is an indication to the phases present in the multiphase mixture. Initial tests show that the sensor is a valuable tool to investigate three-phase flows, which are very common in the oil industry.     

Study of the parametric dependence of erosion wear for the parallel flow of solid–liquid mixtures

The phenomenon of erosion wear due to the cutting action of solid particles in solid–liquid mixture flows has been studied in a slurry pot tester. Special fixtures and design modifications were incorporated in a slurry pot tester in order to ensure that the erosive wear on the wear piece is primarily due to parallel flow of the mixture. Experiments performed at various solid concentrations, particle sizes and velocities, show that the parallel flow wear increases with increase in solid concentration, particle size and velocity. The parametric dependence on velocity is comparatively much stronger as compared to that on either solid concentration or particle size.     

激光衍射粒度测量中的旋滤波方法

激光衍射法测量颗粒粒径过程中,面阵CCD接收到的待测颗粒的衍射图样总是不可避免受到噪声污染,直接影响粒度的反演精度。通过对测试原理及衍射图样的深入分析,提出了采用曲线窗口旋滤波对衍射图样进行预处理的方法,并进行了粒子群粒度反演的数值模拟实验。经过旋滤波处理后的单峰粒子和双峰粒子的粒度分布误差从直接粒度反演的42．36％、46．099／6和39．06％、35．7％分别减小到5．3％、6．17％和6．48％、7．33％,实验结果证明了采用曲线窗口旋滤波方法,粒度分布误差明显降低。     

Three-terminal capacitance cell for stopped-flow measurements of very dilute solutions

A capacitance cell has been designed, constructed, and tested for stopped-flow measurements of very dilute low-relative permittivity liquid solutions. The capacitance cell utilizes a three-terminal design and is connected to ultrahigh sensitivity capacitance bridge. The cell was designed for operating conditions T = 243.15-373.15 K and P = 0-1 MPa and tested with pure anhydrous cyclohexane and with dilute acetone/cyclohexane solutions at 298.15 K and 0.1 MPa under an argon blanket in a thermostated bath with a temperature variation of <0.001 K. Details of the design and materials of construction are reported. The measured relative permittivity of cyclohexane was 2.015 565, in agreement with the literature, and the long term variation of the measurement was +/- 5 x 10(-6). The relative permittivities of the acetone/cyclohexane solutions were very linear (R2=0.9997) in the measured interval of 0.001-0.008 mole fraction. These measurements confirm that the design specifications for stability and resolution/sensitivity of better than 1 x 10(-5) have been realized. Finally, the present online capacitance cell was connected online to an ultrasensitive densitometer and ultrasensitive refractometer and binary acetone/cyclohexane solutions were measured. The measurements of density, refractive index, and relative permittivity were combined to provide a dipole moment of acetone of 2.750+0.005 D, which is in good agreement with literature.     

基于微螺线管电感式传感器的金属颗粒形态对输出特性影响的研究

基于电感测量技术与微流体技术的油液检测芯片, 不仅可以区分出铁磁性和非铁磁性金属颗粒, 还可以对油液中的颗粒进行计数统计和颗粒大小测量,从而判断金属颗粒污染物的来源及设备的磨损状态。通过理论分析、数值模拟及实验验证, 分析不同形态铁磁颗粒退磁场, 研究铁磁颗粒形态对电感式传感器的输出影响。建立理论模型描述不同形状颗粒的退磁因子、磁化场, 以及磁化的金属颗粒产生磁场从而导致线圈电感发生变化。基于模型计算并验证同体积下球形、不同轴长比的圆柱、椭球颗粒的磁场和电感输出, 分析结果显示颗粒越细长、退磁因子越小则越容易磁化, 因此细长颗粒引起传感器的电感变化更大, 另外圆柱形颗粒的电感变化大于旋转椭球型颗粒。     

On-line measurement of particle size distribution and mass flow rate of particles in a pneumatic suspension using combined imaging and electrostatic sensors

This paper presents a novel instrumentation system that uses a combination of electrostatic and digital imaging sensors. An inferential approach is adopted for the mass flow measurement of particles, velocity and volumetric concentration of particles being measured independently. The velocity of particles is determined by cross correlating two signals derived from a pair of electrostatic sensors and the volumetric concentration of particles is obtained using a novel digital imaging sensor, which also provides particle size distribution data. The basic principles and limits of operation of the imaging sensor are discussed and explained. Results obtained from a pneumatic conveyor are presented which demonstrate good performance of the measurement system for both mass flow metering (accurate to about ±6%) and particle sizing (reliable to around ±2.5%). Particle size distribution results are also included and the insensitivity of particle sizing to changes in velocity and concentration is assessed. In addition, on-line sizing results are compared to off-line results, measured using an accepted laser diffraction based instrument, and good agreement is observed. In general, the results obtained are encouraging and the system shows great promise.