On-line non-intrusive particle size measurement of pulverised fuel through digital imaging

This paper presents the basic principles of particle size measurement and latest industrial results recorded using an innovative optical instrumentation system designed to measure the size distribution of particles in a pneumatic suspension.The system is non-intrusive and cost-effective.A low-cost CCD camera is used to capture images of the particulate flow field,which is illuminated by a low-cost pulsed laser sheet generator.The particle size distribution is then determined by processing the particle images through the use of novel processing algorithms.Experimental results obtained in the past on a small scale particle flow test rig have demonstrated that the system is capable of measuring the size distribution of pneumatically conveyed particles with an accuracy of a few percent.For the present paper results obtained when testing the system at a 4 MW industrial test facility are presented.Comparisons are made with both off-line reference data achieved through sieving and on-line laser diffraction data recorded using an intrusive,extractive,Malvern Instruments system.In general there is good agreement between results when considering the characteristics and limitations of the individual methodologies.The novel imaging system shows itself to be rugged,practical and useful under genuine industrial conditions.     

Simultaneous particle size and concentration measurements using a back-lighted particle imaging system

A back-lighted particle imaging system (BLPIS) is developed to simultaneously measure particle size distribution and volume concentration of suspended particles in water. Based upon optical principles, a modified in-focus parameter, incorporating optical conditions, particle shape, overlapping, and depth-of-field variations due to particle size, is developed to identify particles. BLPIS is calibrated with a precise graticule with an accuracy of particle sizes within the measurement uncertainty of image pixel size resolution. For volume concentration, BLPIS employs an adaptive sampling volume methodology that varies with each particle size based upon a critical in-focus parameter value. Experiments show that under lower volume concentration, measured and actual particle size distributions are in good agreement. For higher volume concentration, measured particle concentration is corrected using a Poisson-based distribution to account for overlapping. Overall the volumetric concentration measurement is reliable and accurate with a relative error of approximate 10%. Finally BLPIS is applied to accurately measure both size and concentration of flowing particles near the bottom boundary with resuspension and sedimentation processes.     

动态光散射颗粒分布软测量

考虑传统动态光散射颗粒粒度分布测量用的反演算法复杂、精度不够、抗噪能力差,本文基于大数据思想,提出了一种动态光散射颗粒分布软测量方法。该方法通过调节颗粒粒度分布形状参数获得大量自相关函数及其对应颗粒分布的数据;使用这些数据对子学习机进行训练。最后,针对训练数据维数较高的特点对传统Bagging算法进行改进,并利用改进的Bagging集成算法集成子学习机以提高软测量模型的精度及泛化能力。通过模拟单峰数据和对300nm标准粒径进行软测量开展了验证实验。结果表明,该方法能够较好地测量出不同动态光散射颗粒分布的峰值及分布宽度,模拟单峰数据测量峰值精度可达1nm,300nm和503nm,标准粒径测量精度分别可达3nm和4nm,优于一般的反演算法。该软测量方法为动态光散射颗粒分布测量开辟了新的途径。     

Identification of gas/solid two-phase flow regimes using electrostatic sensors and neural-network techniques

In the gas/solid two-phase system, solid particles can accumulate a large number of electrostatic charges because of collision, friction and separation between particles or between particles and the wall. Through the detection and processing of the induced fluctuation charge signal, a measuring system can obtain two-phase flow parameters, such as flow regime, concentration and velocity. A novel methodology via introducing the characteristics of speech emotion recognition into flow regime identification is proposed for improving the recognition rate in gas/solid two-phase flow systems. Three characteristics of electrostatic fluctuation signals detected from an electrostatic sensor are extracted as the input of back propagation (BP) neural networks for flow regime identification. They are short-term average energy, Mel-frequency cepstral coefficients (MFCC) and cepstrum. The results show that the method based on each characteristic of the electrostatic fluctuation signal and BP neural networks can identify the three flow regimes of gas/solid two-phase flow in a horizontal pipe, and the identification rate of the method based on the three characteristics and BP neural networks is up to 97%, much higher than the methods based on a single characteristic.     

Combining high mass resolution and velocity imaging in a time-of-flight ion spectrometer using pulsed fields and an electrostatic lens

We describe a momentum resolving time-of-flight ion mass spectrometer that combines a high mass resolution, a velocity focusing condition for improved momentum resolution, and field-free conditions in the source region for high resolution electron detection. It is used in electron-ion coincidence experiments to record multiple ionic fragments produced in breakup reactions of small to medium sized molecules, such as F(3)SiCH(2)CH(2)Si(CH(3))(3). These breakup reactions are caused by soft x rays or intense laser fields. The ion spectrometer uses pulsed extraction fields, an electrostatic lens, and a delay line detector to resolve the position. Additionally, we describe a simple analytical method for calculating the momentum from the measured hit position and the time of flight of the ions.     

Review of certain key issues in indirect measurements of the mass flow rate of solids in pneumatic conveying pipelines

On-line mass flow measurement of particulate solids in pneumatic conveying pipeline is a technically challenging area, where mass flow measurement presents a range of problems. These problems are not normally relevant to a single phase flow, but are always involved in gas–solids two-phase flows, like inhomogeneous distribution of solids over the pipe cross section, irregular velocity profiles, variations in particle size, moisture content, and deposition of fine particles on the inner wall of the pipeline. These variables may affect the response of a solids flow meter in ill-defined ways. All of these make the design and the calibration of solids’ mass flowmeter more difficult. Based on a review of non-invasive mass flow measurements of particulate solids, this paper summarizes and highlights several key issues, which often rely on structures of sensors or measurement methods, in indirect mass flow metering of pneumatically conveyed solids. They are: (i) spatial filtering effect; (ii) averaging effect; (iii) measurement resolution and sensitivity of array structures in tomography sensors.     

成像标定法测量半导体激光器慢轴远场分布

利用远场成像及标定对比方法,建立了半导体激光器慢轴远场分布的CCD测量系统。介绍了测量的原理和测量系统的组成,并给出了半导体激光器慢轴远场分布的测量结果。实验结果表明,该方法实时性好,测量快速、准确,人为误差因素少,适合仪器化。     

Analysis of flow distribution from high-speed flow actuator using particle image velocimetry and digital speckle tomography

A variety of active flow control (AFC) methods are typically used in low-speed applications; however, the AFC techniques that are available for high-speed, supersonic applications are very limited. Under AFOSR (Air Force Research Laboratory) sponsorship, The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is investigating a device that is intended for high-speed flow control; it is called the SparkJet actuator, which manipulates high-speed flows without active mechanical components. To date, actuator characterization has included computational and experimental techniques including parametric studies and flow visualization techniques to investigate the operation of the SparkJet device under various conditions. This paper focuses on the experimental flow measurement techniques that have been implemented. The results will be used for validating prospective computational studies that investigate the detailed characteristics of the SparkJet’s discharge and cooling stages after an energy deposition pulse. Current efforts include the use of high- resolution particle image velocimetry (PIV) to quantify the quiescent air operation of a single SparkJet pulse. However, the proper seeding of the SparkJet cavity continues to be challenging and has led to the use of digital speckle tomography (DST) to measure the temperature distribution in the core of the SparkJet plume. In this study, improved PIV techniques were used to acquire a higher-resolution image of the SparkJet-entrained flow. These PIV results show that the peak velocity in the entrained flow is around 53 m/s and the plume is sustained for 75–100 μs. Additionally, the DST data show a peak temperature of 1616.3 K at 75 μs and provide supporting information for interpreting the PIV data. These results are intended to calibrate and build confidence in a computational model.     

Experimental investigation of particle distribution in a flow through a stenosed artery

The particle distribution of a dilute solid-liquid suspension through a stenosed arterial geometry was investigated. Particle image velocimetry (PIV) was used to determine the velocity as well as to acquire the flow images. The light intensity scattered by particles was evaluated to determine the particle distribution. Flow separation exists where the flow emerges from the stenosis throat. From the PIV images, the particle density distribution exhibited differing non-uniform characteristics which vary with flow rate, particle size and particle concentration. At low flow rates, a particle-free layer is formed. As the flow rate is increased, particles accumulate in concentric recirculation orbits within the downstream vortex. Particles with larger size and higher concentration tend to accumulate more towards the center of the vortex.     

Measurement of mass flow rate and evaluation of heat transfer coefficient for high-pressure pneumatic components during charge and discharge processes

Both the mass flow rate and heat transfer characteristics are significant factors to the flow behavior of the high-pressure air; however, they are not easy to be obtained by analytical model during discharge and charge processes. In this paper, the mass flow rate characteristics of high-pressure pneumatic components (HPPC) are measured by a compounding approach; two components under test with the same geometry and dimension are needed to be connected in series. Both the effective cross-section area and critical pressure ratio of HPPC are determined accurately, and only the pressure variation and the steady-state temperature of air in the chamber are utilized. The compared results between experimental and simulation data show that the accuracy of the measured effective cross-section area and critical pressure ratio of the HPPC is high when the sonic and adiabatic releasing time is less than 2 s. And then, a new combined method of calculating the heat transfer coefficient during discharging and charging processes for the high-pressure air is proposed. The computational fluid dynamics (CFD) method is used to illustrate the intensity of heat exchange between the high-pressure air inside the chamber and outer atmosphere. The dynamic flow behavior is analyzed based on the tested flow rate characteristics of HPPC, mixed heat transfer theory and numerical results. The results show that the heat-transfer coefficient during charge process is much greater than discharge process, and the forced convection heat exchange happened owing to the strong “air agitation” during the charge process. The experimental results also validate that the proposed method of calculating the transient heat transfer coefficient is more reasonable to describe the heat transfer behavior. The findings may also have general implication in the development of the design and analysis of the high-pressure pneumatic system.     

Optimization of flow rate measurement using piezoelectric accelerometers: Application in water industry

This paper presents a method for measuring flow rates in pipelines based on the flow induced vibration principle using water as fluid, eliminating the need for interrupting the flow and opening of the pipeline for installation of traditional water flow meters. Experimental measurements are carried out in an accredited laboratory for calibration of rate flow meters and a metrological validation, followed by an uncertainty evaluation, are presented. Data analysis is accompanied by a method of optimization that minimizes adjustment errors of measurement using regression by parts and by the selection of the optimum period to estimate more accurately the flow rate. The results meet the specifications of Brazilian Metrology Institute.     

The pressure distribution in and flow characteristics of wide-angle diffusers using perforated plates for flow control with application to electrostatic precipitators

To perform effectively, electrostatic precipitators require a highly uniform velocity distribution in the treatment zone. This requirement places particular demands on the design of the wide-angle diffuser upstream of the treatment zone. To generate satisfactory diffuser exit velocity profiles, perforated plates are installed within the diffuser. This paper provides a report of an experimental investigation of the nature of the flow generated by installing two perforated plates in the diffuser. Detailed measurements of the static pressure distribution and flow patterns are reported. The effects of altering the porosity and locations of the perforated plates on the flow and pressure loss characteristics are considered.     

Field measurement and estimation of ventilation flow rates by using train-induced flow rate through subway vent shafts

This study measured and estimated the subway vent shaft air flow rate induced by moving trains in the tunnel. This work estimated the flow rate via the tunnel structure and train movement to determine the quantitative effect of vent shafts as air purification systems of natural ventilation to improve the air quality management of a subway. The amount of air suctioned into the tunnel is significantly larger than that vented from the tunnel. Thus, placing vent shafts near subway stations is desirable for natural ventilation systems. Experimental approaches to measure train-induced flow rates have not yet been published. Results of this study provide useful fundamental data to study the natural ventilation in a subway. Therefore, this study suggested the significant design factors required to control indoor air quality in a subway.     

LDV measurement,flow visualization and numerical analysis of flow distribution in a close-coupled catalytic converter

Results from an experimental study of flow distribution in a close-coupled catalytic converter (CCC) are presented. The experiments were carried out with a flow measurement system specially designed for this study under steady and transient flow conditions. A pitot tube was a tool for measuring flow distribution at the exit of the first monolith. The flow distribution of the CCC was also measured by LDV system and flow visualization. Results from numerical analysis are also presented. Experimental results showed that the flow uniformity index decreases as flow Reynolds number increases. In steady flow conditions, the flow through each exhaust pipe made some flow concentrations on a specific region of the CCC inlet. The transient test results showed that the flow through each exhaust pipe in the engine firing order, interacted with each other to ensure that the flow distribution was uniform. The results of numerical analysis were quali-tatively accepted with experimental results. They supported and helped explain the flow in the entry region of CCC.     

Application of averaging bidirectional flow tube for measurement of single-phase flow rate in a piping system

A new instrument, an averaging bidirectional flow tube (BDFT), is proposed to measure single-phase flow rates. This averaging BDFT has unique measuring characteristics foremost among which is the capability to measure bidirectional flow and insensitivity of the fluid attack angle. Single phase calibration tests were conducted to demonstrate the performance of the averaging BDFT. Likewise, to enhance the applicability of the averaging BDFT on various flow conditions, flow analyses using CFD code were performed focusing on design optimization of the BDFT. The calibration test results indicated that this averaging BDFT has a linearity within 0.5 % in the Reynolds (Re) number range of above 10,000 where it is meaningful in terms of application. The flow analyses results demonstrate a good linearity of the averaging BDFT with various design features. Therefore, averaging BDFT can be applied for measurement of flow rates within a wide range of flow conditions. This paper was recommended for publication in revised form by Associate Editor Won-Gu Joo Kyoung-Ho Kang received his B.S. and M. S. degrees in Nuclear Engineering from SNU (Seoul National University), KOREA in 1993 and 1995, respectively. He then received his Ph.D. degree in Nuclear and Quantum Engineering from KAIST (Korea Advanced Institute of Science and Technology) in 2009. Dr. Kang is currently a senior researcher at the Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Kang’s research interests include analysis and experiments for the nuclear safety, thermal hydraulics, and experiments and modeling for the severe accidents. Byong-Jo Yun received his B.S. degree in Nuclear Engineering from SNU (Seoul National University), KOREA in 1989. He then received his M.S. and Ph.D. degrees from SNU in 1991 and 1996, respectively. Dr. Yun is currently a principal researcher at the Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Yun’s research interests include analysis and experiments for the nuclear safety, thermal hydraulics, two-phase flow, scaling analysis, and development of instrumentation for two-phase flow. Dong-Jin Euh received his B.S. degree in Nuclear Engineering from Seoul University, Korea, in 1993. He then received his M.S. and Ph.D. degrees from same university in 1995 and 2002, respectively. Dr. Euh is currently a researcher at thermal hydraulic safety research department of Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Euh’s research interests include two-phase thermal hydraulics in the Nuclear Systems and Fundamental Phenomena. Won-Pil Baek has been working at KAERI as the general project manager (director) for development of nuclear thermalhydraulic experiment and analysis technology since 2001. He received his B.S. degree in nuclear engineering from Seoul National University and his M.S. and Ph.D. degrees from KAIST. In 1991–2000, he worked for KAIST as a researcher and research professor. Currently he also serves as an executive editor of the Nuclear Engineering and Technology, an international journal of the Korean Nuclear Society. His research interests include critical heat flux, integral effect tests, modeling, nuclear safety, and advanced reactor development.     

Particle velocity detection and measurement in two-phase flow using combined electronic logic system and LDA technique

A new experimental method to measure the velocity and fluctuations of a solid–liquid suspension is proposed in this work. This method based on laser anemometry with Doppler effects consists of an association of laser velocimetry and an electronic logic circuit placed at the reception. This circuit was developed in order to distinguish between signals from the continuous phase (water) and those of the solid particles (glass beads) and therefore to detect the presence of large particles (larger than the laser wavelength) in the measurement volume. The present experimental method is limited to small volumetric concentrations lower than 2%. Indeed, when the value of 2% is exceeded, the suspension becomes a very diffusing medium and prevents the propagation of laser beams in the flow in an ascending vertical glass pipe. The results show that a fine particle suspension, which represents a tracer, behaves as a homogeneous fluid. For large particles, we confirmed the existence of a slip velocity and the effect of particle concentration on the turbulence intensity.     

蒸汽管网流量测量误差的在线修正方法与应用

针对蒸汽管网中蒸汽流量的测量误差较大,导致蒸汽在管理和调度中容易造成能源浪费的问题,提出了一种基于主元分析(principal component analysis,PCA)的蒸汽流量测量误差在线修正方法,首先,利用主元分析法对蒸汽管网中各节点的流量测量值进行滤波,去除随机性误差;其次,利用基于主元分析模型的平方预报误差(squared prediction error,SPE)判断蒸汽管网的负荷工况;然后,综合考虑流量的大小和方差,采用Lagrange乘子法对仪表的测量偏差进行数据协调;最后,利用残差矩阵对下一个统计周期内的数据进行在线修正.将该算法应用到钢铁企业的蒸汽管网中,实验结果表明,基于所提算法的误差修正软件对蒸汽流量测量误差修正后,累积误差比原来减少了99.09％.有效地消除部分检测误差,使蒸汽管网流量在总体上趋于供需平衡.     

Investigation of droplet size distribution in two-phase flows using a combined method for recording droplet fluorescence and diffraction scattering of light

A prototype of a combined measurement system (MS) based on the fluorescent and small-angle methods of determining the parameters of a fuel-air spray using a pulsed laser as a light source and a color digital video camera to record spray sections was designed and tested. The tests of the MS showed that it has good performance and is suitable for determining the characteristics of advanced atomizers in a pressure chamber. Spatial concentration distributions of aerosols generated by a centrifugal atomizer were studied. Distributions of time-averaged Sauter diameters of droplets, their concentration, and the circumferential inhomogeneity of droplet concentration in the spray cross section were obtained. A study of fuel atomization from a plate was performed showing the possibility of using this device in power plants to improve the atomization performance compared to the atomization of a free jet in crossflow.