Uncertainty and intrusiveness of three-layer wire-mesh sensor

A wire-mesh sensor (WMS) has been applied to estimate the bubble velocity of an air-water bubbly flow in a vertical channel with a square cross-section. The WMS provides instantaneous cross-sectional gas fraction distributions which are measured by detecting the local electrical conductivity between two electrode wires crossing each other at right angles. The applied WMS has three planes of wire grids separated by 1.5 mm in the axial direction. The wires of the central grid are used as transmitter electrodes, while the wires of the two external grids are connected to the receiver inputs of the electronic unit. In this way, the sensor has two measuring planes, located between the transmitter grid and both receiver planes. Individual bubble diameters are calculated from the measured gas fraction data by using a bubble identification algorithm, and the bubble velocity is evaluated by cross-correlating the instantaneous gas fraction profiles. In case of WMS measurements, the intrusive effects caused by the wires cannot be neglected. In this study, the effect of the intrusive WMS on the bubble velocity was studied by high speed camera (HSC) observation. Bubble parameters were extracted from both WMS and HSC data. A comparison of bubble size and velocity was carried out for each bubble individually. It was found that bubbles are strongly decelerated when they collide with the wire grids in case of low liquid velocities. The effect decreases with growing liquid velocity and finally turns into a slight acceleration which corresponds to the degree of the cross-section obstruction by the wires.     

Applications of wire-mesh sensors in multiphase flows

This article offers an overview of the applications of the wire-mesh sensor (WMS) in different environments. It presents a critical review of the literature, with relevant and recent implementations, remarkably in gas–liquid and liquid–liquid flow, comparing it with other techniques. In addition, it is shown how the sensor is adapted to each application and its different geometries, showing its flexibility. The advantages and disadvantages of the use of the WMS are analyzed. This technique can provide information about local, chordal, cross-section or in-situ volume profiles/distributions of phase fraction; velocities, size and distributions of droplets/bubbles; frequency of periodic structures; interfacial area; film thickness; flow regimes and thermal distribution.     

Robust computational framework for wire-mesh sensor potential field calculations

With the development of the next generation of nuclear reactor safety system codes fast underway, increased importance has been placed on enhancing physical closure correlations and amassing representative benchmark-quality experimental data for validation purposes. Wire-mesh sensors, a reputable experimental measurement technique with sufficient spatial and temporal resolution to serve such goals, and related data reconstruction algorithms have been the subject of renewed interest as researchers attempt to characterize their measurement uncertainty. To assist in such investigations, the present work establishes a comprehensive numerical framework with which to quantify the electric potential field around wire-mesh sensors. Using the finite-volume foundations of OpenFOAM, a numerical solution algorithm is developed to predict the transmitted electric current between transmitter and receiver electrodes for both homogeneous and heterogeneous electrical conductivity fields. A detailed verification against seminal numerical calculations and robust validation procedure is included to ensure the accuracy of the proposed methodology. Parametric studies of spherical bubble diameter, lateral crossing position, and spheroidal shape influence are conducted to provide preliminary insights into wire-mesh sensor operation and the suitability of various calibration approaches. Observed trends in the transmitted currents reveal overshoots relative to calibration conditions, which are fundamentally linked to the maldistributed electric potential field in heterogeneous bubbly flows. The present investigation offers a vital first step towards a comprehensive multi-physics model of multiphase flow around a wire-mesh sensor.     

Performance evaluation of conductivity wire-mesh sensors in vertical channels

This article presents a comprehensive and critical discussion of available literature on conductivity wire–mesh tomography as well as some complementary original analysis. Wire-mesh tomographs were first classified into different categories, depending on their principles of operation, and then the discussion was focused on the most commonly used type, namely, the wire–mesh sensor (WMS) in vertical channel flows. The main applications of WMS were outlined and the properties that can be determined from WMS signals were identified, together with the corresponding procedures. WMS performance and the factors that affect this performance were evaluated in detail using results of previous investigations as well as new analysis and data. The principles of operation and main applications of global wire–mesh tomographs were then described. This article finally presents several examples of wire–mesh tomography applications in multicomponent flows.     

Micro wire-mesh sensor for two-phase flow measurement in a rectangular narrow channel

A micro wire-mesh sensor (μWMS) based on an electrical conductivity measurement between electrodes installed on the walls has been developed for gas–liquid two-phase flow measurements in a narrow rectangular channel. This measuring method applies a principle of conventional wire-mesh tomography, which can measure the instantaneous void fraction distributions in the cross-section of the relatively large flow channel. In two-phase flow measurement using μWMS the void fraction distributions in the narrow channel were obtained by the measured conductivities between electrodes arranged on each wall. Therefore, the gas phase structures and the bubble behaviors can be investigated in the flow channel with narrow gap. In the present paper, a μWMS for the air–water flow between parallel flat plates with a gap of 3 mm was developed and simultaneous measurements with a high speed video camera were conducted to compare the measured results in bubbly flow.     

Measurement of film fluctuations and aerated characteristics during gas-liquid slug-churn flow transition by wire-mesh sensor

Vertical upward gas-liquid slug flows are frequently encountered in chemical processes and petroleum industries. The measurement of the film fluctuations and the aerated characteristics is of great significance for uncovering the mechanism of slug-churn flow pattern transitions. In this study, a conductance wire-mesh sensor (WMS) measurement system is designed based on a Field Programmable Gate Array (FPGA) to visualize the structures of vertical gas-liquid flows. Liquid film flooding is a significant factor prompting the transition from slug to churn flow. Based on the WMS data, the 3D film structures are derived to indicate film instability during the flow pattern transition. Three types of film fluctuations in stable slug flow, unstable slug flow, and churn flow are presented. Liquid slug aeration is another important factor contributing to the slug-churn flow transition. The spatial distribution and the diameters of the gas bubbles in the liquid slug are detected by the WMS. The coalescence behavior of the bubbles is uncovered. Finally, mechanistic models based on the film flooding and slug aeration are constructed to predict the boundary of the flow pattern transition. The performance of the film flooding model and slug aeration model in predicting the onset of churn flow is evaluated.     

Comparison between wire-mesh sensor and ultra-fast X-ray tomograph for an air–water flow in a vertical pipe

A comparison between ultra-fast X-ray CT and a wire-mesh sensor is presented. The measurements were carried out in a vertical pipe of 42 mm inner diameter, which was supplied with an air–water mixture. Both gas and liquid superficial velocities were varied. The X-ray CT delivered 263 frames per second, while the wire-mesh sensor was operated at a frequency four times higher. Two different gas injectors were used: four orifices of 5 mm diameter for creating large bubbles and gas plugs and a sintered plate with a pore size of 100 μm for generating a bubbly flow. It was found that the wire-mesh sensor has a significantly higher resolution than the X-ray CT. Small bubbles, which are clearly shown by the wire-mesh sensor, cannot be found in the CT images, because they cross the measuring plane before a complete scan can be performed. This causes artifacts in the reconstructed images, instead. Furthermore, there are large deviations between the quantitative information contained in the reconstructed tomographic 2D distributions and the gas fractions measured by the sensor, while the agreement is very good when the gas fraction is obtained by a direct evaluation of the X-ray attenuation along the available through-transmission chords of the tomography set-up. This shows that there is still potential for an improvement of the image reconstruction method. Concerning the wire-mesh sensor it was found that the gas fraction inside large bubbles is slightly underestimated. Furthermore, a significant distortion of large Taylor bubbles by the sensor was found for small liquid velocities up to 0.24 m/s. This effect vanished with growing superficial water velocity.     

Experimental investigation on the void fraction characteristics of a sudden expansion tube using wire-mesh sensors

Void fraction is an essential parameter of gas-liquid two-phase flow and experiments were executed to investigate the void fraction fluctuation characteristics of gas-liquid two phase flow through a sudden expansion tube. Two 16 × 16 wires mesh sensors were applied to measure the phase distribution of upstream pipe(pipe-32) and downstream pipe(pipe-50). The superficial gas velocity is in the range of 3.46 m/s - 22.46 m/s and the superficial liquid velocity ranges from 0.034 m/s to 0.414 m/s. Flow pattern evolution of upstream and downstream pipes was reconstructed and compared. The experiment results show that, in contrast to pipe-32, the void fraction of pipe-50 shows different trends with the increase of liquid and gas velocity. Liquid-carrying capacity is essential in the relationship between the void fraction of pipe-32 and pipe-50. The critical superficial liquid and gas velocities are proposed to characterize the liquid-carrying capacity. The maximum critical superficial gas and liquid velocity is 15.56 m/s and 0.207 m/s, respectively. Besides, a model is proposed to describe the relationship of void fraction between pipe-32 and pipe-50. It is found that the prediction error is less than ±10% in the case of annular flow.     

Experimental PIV and LIF characterization of a bubble column flow

Experimental 2D Particle Image Velocimetry (PIV) measurements, with uniform background lighting and Laser Induced Fluorescence (LIF) of the tracking particles, were performed in order to characterize the air-water biphasic flow and the 2D bubble column rising velocity in static water. Some applications require knowledge of the simultaneity of two-phase flow characteristics. The two phase flow air/water are common application in industry as chemical, hydraulic and nuclear industry, water treatment by aeration, and measurements are implemented to characterize the behaviour of the air bubbles column flow. The bubble flow studied in this paper is related to the optimization of the aeration in hydraulic turbines with micro-bubbles. The first step of this study, presented in the paper, is a complete characterization of a bubble column issued from a metallic sparger with holes of 0.5 mm diameter. For its complete characterization is determined simultaneously, via image processing technics, the flow velocity field induced by the column of bubbles in water, and the bubbles features: the bubble ascension velocity, diameter variation, interfacial area and shape factor. The results are compared with bibliographical data.     

Pulverized coal flow metering on a full-scale power plant using electrostatic sensor arrays

On-line continuous monitoring of pulverized coal in fuel injection pipes will allow power plant operators to optimize fuel conveying conditions and ultimately to achieve higher combustion efficiency and lower atmospheric emissions. This paper presents the design, implementation and trials of a prototype instrumentation system for the on-line measurement of pulverized coal on a full-scale power plant. An array of three identical arc-shaped electrostatic electrodes is housed in a sensing head to derive particle flow signals. Pulverized coal flow parameters such as velocity, mass flow rate and fuel distribution among the injection pipes from the same pulverizing mill are obtained by processing the signals and fusing the resulting measurements. On-plant demonstration trials on 560 mm bore pneumatic conveying pipes feeding a 600 MW boiler were undertaken following system evaluation tests on a 50 mm bore laboratory test rig. Experimental results demonstrate that reliable monitoring of pulverized coal flow parameters is achieved and that the system is able to track both transient and long-term fluctuations of pulverized coal flow in fuel injection pipes under real power plant conditions.     

The monitoring of the two phase flow-annular flow type regime using microwave sensor technique

Accurate monitoring of a multiphase fluid flow in a dynamic pipeline is a significant problem in the oil industry. For efficient management of oil field wells, a real-time online system with capabilities to monitor fractions of oil, gas and water in oil production pipelines is required. These parameters determine the oil quality and inform how much water, oil and gas is produced from oil wells. This paper reports on the development of a novel non-intrusive sensor, which is based on electromagnetic waves cavity resonator. It determines and monitors the percentage volumes of each of the two phases (oil and gas) in the pipeline using the resonant frequencies shifts that occur within the resonator. A laboratory prototype version of the sensor system was constructed and tested. Experimental results were in good correlation with theoretical model that was simulated with High Frequency Structure Simulation (HFSS) software. Reported system will form the basis for the advanced real-time multiphase fluid composition monitoring platform.     

Computational modeling of bubbly flows in differential pressure flow meters

This paper addresses bubbly flow modeling within Venturi tubes and nozzles using the two-fluid model. The effects of non-drag forces as virtual mass and the so-called “transversal forces” such as lift and wall lubrication are investigated in the context of the two-fluid model. As expected, the transversal forces have an important influence on void distribution as long as the virtual mass affects the pressure drop along the contraction, which is the main parameter for the flow rate measurement. Models for the virtual mass and lift forces were implemented via user routines in commercial computational fluid dynamics (CFD) software, as the models embedded within these packages, specifically for virtual mass, were found not to be adequate for the purpose of this study. The models are validated against results from the literature and pressure drop measurements along a Venturi tube, developed in this work. Additionally, some experimental visualizations were used to make a qualitative comparison with predicted void distribution.     

一种新型硅压阻式流速流向传感器的设计

本文设计了一种基于体微机械加工技术、SU-8-光刻胶工艺和压阻检测的新型硅压阻式流速流向传感器.该传感器由立柱和支撑梁构成,这种结构将流体的流速流向信息转化为立柱的倾斜和相应的梁的变形,通过4根正交梁端部的压阻应变计来测量梁的变形.通过测量压电电阻的阻值变化就可以得到流体的流速和流向.利用惠斯通电桥来获得正弦电压输出.理论分析了器件的结构变形和电压输出,并用有限元方法进行了验证.为该传感器设计了一套基于键合技术的体微机械加工工艺.     

气固两相流流速测量系统的传感器设计

介绍一种用于测量气固两相流流速的传感器,阐述了其工作原理,对传感器的结构和随机噪声提取电路进行设计和分析,试验证明该传感器能够检测微弱的随机流动信号。     

Performance analysis of a single-wire capacitance sensor for interface level measurement in stratified multiphase flows

A single-wire capacitance sensor can be used to measure the interface level of a conductive liquid in a stratified multiphase flow. This type of capacitive sensor uses the conducting core in an insulated wire as its first electrode, and the conductive fluid as its second electrode, separated by the wire insulation, producing a coaxial capacitor with a variable electrode length linearly correlated to the liquid level. Therefore in theory, there should be a linear relationship between the liquid level and measured capacitance value. However, at low liquid levels, the authors have observed a noticeable departure from the theoretical correlation in the way of an upward offset. The cause for such a departure is investigated by means of a simplified model geometry and attributed to an additional capacitance between the wire conductor and conductive plane provided by the liquid interface. Analytical and numerical modelling have been carried out to better understand this effect. Recommendations are given on how to correct it.     

Experimental investigation of gas-liquid flow in a vertical venturi installed downstream of a horizontal blind tee flow conditioner and the flow regime transition

A venturi device is commonly used as an integral part of a multiphase flowmeter (MPFM) in real-time oil-gas production monitoring. Partial flow mixing is required by installing the venturi device vertically downstream of a blind tee pipework that conditions the incoming horizontal gas-liquid flow (for an accurate determination of individual phase fraction and flow rate). To study the flow-mixing effect of the blind tee, high-speed video flow visualization of gas-liquid flows has been performed at blind tee and venturi sections by using a purpose-built transparent test rig over a wide range of superficial liquid velocities (0.3–2.4 m/s) and gas volume fractions (10–95%). There is little ‘homogenization’ effect of the blind tee on the incoming intermittent horizontal flow regimes across the tested flow conditions, with the flow remaining intermittent but becoming more axis-symmetric and predictable in the venturi measurement section. A horizontal (blind tee) to vertical (venturi) flow-pattern transition map is proposed based on gas and liquid mass fluxes (weighted by the Baker parameters). Flow patterns can be identified from the mean and variance of a fast electrical capacitance holdup measured at the venturi throat.     

热膜式空气质量流量传感器块联模型结构辨识

同时利用稳态和动态校准数据,辨识了基于Hammerstein模型的热膜式空气质量流量(MAF)传感器的模型结构.在用多项式逼近静态非线性特性的基础上,动态线性环节分别选取带外生输入的自回归(ARX)模型、输出误差(OE)模型和Box-Jenkins(BJ)模型结构,采用交叉准则法进行参数估计和阶次选择,通过残差分析和仿真比较对模型进行检验.结果表明,用估计数据选择阶次时,最终预报误差(FPE)准则与最终输出误差(FOE)准则具有良好的一致性,基于预测误差法的2阶OE模型和BJ模型均可用于热膜式空气质量流量传感器Hammerstein模型动态线性环节的建模.     

Hydrodynamics and particle mixing/segregation measurements in an industrial gas phase olefin polymerization reactor using image processing technique and CFD-PBM model

Particle size distribution (PSD) has a significant impact on the performance of fluidized bed reactors due to uneven distribution in the segregation and mixing phenomena. This paper develops a new method of digital image processing that investigates the hydrodynamics of an industrial gas phase olefin polymerization reactor and studies the fluidization structure of a wide range of particle size distribution in an industrial gas phase polymerization reactor by means of a CFD-PBM coupled model, where the direct quadrature method of moments (DQMOM) was implemented to solve the population balance model. It was shown that the applied parameter assumptions and closure laws were appropriately chosen to satisfactorily predict the available operational data in terms of pressure drop and bed height. The transient CFD-PBM/DQMOM coupled model and image analysis technique are then implemented extensively to analyze bubble fluidization structure and segregation phenomena at different velocities. The particle segregation indicates that the small bubbles present in the bed are unable to induce vigorous mixing at low superficial gas velocity while particle mixing improves at a velocity above the minimum fluidization velocity. Further, the predicted results show higher axial segregation phenomena when compared to the radial direction.     

A study of signal noise reduction of the mass air flow sensor using the flow conditioner on the air induction system of heavy-duty truck

The mass air flow meter is a critical sensor that works based on thermal hot wire technology, used to determine the fuel to be injected into the cylinder and calculate the fuel-air ratio. In order to measure the airflow rate accurately, the flow should be uniform and smooth upstream of the sensor. The flow disturbance with a short straight length upstream of the flow meter results in the noise of the sensor signal. This noise causes unstable mass flow measurement on the system. Flow conditioners can be used to smooth the velocity profile of the flow. In this study, experimental and numerical methods were used to characterize the performance and operating accuracy of the mass flow meter used in heavy-duty truck applications. The flow conditioners were implemented to smooth the velocity profile around the mass flow meter that was disrupted by bends. The flow structures with and without flow conditioner were examined using Particle Image Velocimetry (PIV) to measure the time-averaged velocity. As well as the validated computational fluid dynamics (CFD) model provides data to understand the flow uniformity effect of the conditioner on the mass airflow (MAF) sensor. The optimization study was performed using a full factorial design of experiment (DOE) for flow conditioner design. A robust methodology was developed for the flow conditioner characteristics and mass airflow sensor implementation on the air induction system.     

Gas-liquid flow patterns visualization in a self-priming centrifugal pump

The self-priming pumps are ubiquitous in gas-liquid mixtures lift and transportation areas. The fast self-priming time is a vital evaluation index for a self-priming pump. However, the bubble movement path and the bubble size distribution characteristics during the self-priming process are still an open issue. This paper aims to obtain the gas-liquid flow patterns inside a centrifugal pump during the self-priming process and evaluate the effect of the rotational speed and the position of the back-flow hole on the self-priming time through experiments. A centrifugal pump with a double-blade was designed as a visualization prototype. The high-speed photography technology was used to capture the bubble motion and size in the pump during the self-priming process. The bubble image processing method was used to identify the bubble size distribution in the diffuser during the self-priming process. The bubble number and size distribution images were presented to understand the influence of the rotational speed and the position of the back-flow hole. The higher rotational speed accelerates the gas-liquid mixing rate and shortens the self-priming time. However, there is a limited value of the self-priming time as the speed goes up to a certain high level. Moreover, the position of the back-flow hole slightly affects the self-priming time.