W.Q. Yang

The University of Manchester, Manchester, ENG, United Kingdom

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Publications (37)30.78 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Two circular electrical capacitance tomography (ECT) sensors have been designed and used to monitor the solids flow in a cold circulating fluidised bed (CFB) with an external heat exchanger (EHE). The ECT sensors have eight electrodes and were mounted in the side tube and return tube above the EHE via pneumatically controlled loop seal respectively. Dynamics test with different process conditions are given. Image reconstruction results in the cross-sectional of the two tubes are compared and averaged measured signals are given. The results indicate that the solid flow can be controlled in the EHE based on ECT measurement.
    Imaging Systems and Techniques (IST), 2012 IEEE International Conference on; 01/2012
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    ABSTRACT: In this study, operating conditions for a batch fluidised bed dryer are found that achieve the specifications on the final moisture level, while minimising the energy consumption. The operating conditions are obtained by solving an optimisation problem, where the specification for the final moisture content of the bed is included as a constraint. The optimisation is based on a lumped mechanistic model that describes the heat and mass transfer between solid, gas and bubble phases in the bed. Experimental validation of this model shows that it can be used to predict the particle moisture content and temperature profiles during the drying process and it is shown that the wall temperature has a major effect on the predictions. Compared to the standard approach of maintaining the inlet air temperature and flow rate at constant values, the optimal operating conditions for a lab-scale bed dryer reduce the energy consumption by 26% and shorten the duration of a batch by 20%min.
    IET Control Theory and Applications 03/2010; · 1.72 Impact Factor
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    H. G. Wang, W. Q. Yang
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    ABSTRACT: To investigate the effect of moisture content, excitation frequency and normalisation model on image reconstruction with a fluidised bed dryer, an electrical capacitance tomography (ECT) sensor was mounted near the bottom of the drying chamber. An ECT system based on an HP4128 impedance analyser was used to measure capacitance and loss conductance between the electrode pairs in the sensor. It has been found that the capacitance depends on not only the particle moisture but also the excitation frequency. With a low moisture content, the relationship between capacitance and frequency is simple and linear. With a high moisture content, however, the relationship becomes more complex and non-linear. For image reconstruction, different normalisation models have been used: series, parallel, Maxwell and Böttcher models. The results show that with a low moisture content, these models give nearly the same image errors. With the increase in moisture content, the difference between these models becomes more and more obvious. With different gas–solids flow patterns, the four models also give slightly different images. In the end of this paper, solids distribution and averaged solids concentration profile for dynamic test with different excitation frequencies in a fluidised bed dryer are given.
    Powder Technology - POWDER TECHNOL. 01/2010; 199(1):60-69.
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    ABSTRACT: Currently, two main methods are used to take online measurement of the solids moisture in fluidised bed dryers, namely microwave resonance and near infrared spectroscopy. In this paper, a new online approach to solids moisture measurement of batch fluidised bed dryers by electrical capacitance tomography (ECT) is presented for the first time. Based on online measurement of solids moisture, it is possible to implement feedback control and process optimisation of batch fluidised bed drying processes, aiming to increase the operation efficiency and to improve product quality. A twin-plane ECT sensor with eight electrodes in each plane is mounted in the bottom of a glass fluidisation chamber. From the adjacent electrode pairs, the water content of the solids is estimated based on the correlation between the moisture content and the permittivity value. To reduce measurement error, the effect of temperature on moisture measurement is compensated. The fluidisation velocity is estimated by a semi-empirical function based on the measured water content. The acquired information is sent to a controller to adjust the air flow rate of the fluidised bed dryer. To validate the moisture measurement by ECT, a mathematical model has been developed, based on the measured temperature and relative humidity of the outlet air. The Landweber iteration method is applied to reconstruct images. The averaged solids concentration along the radial direction at different fluidisation conditions is given and compared with results by the linear back-projection (LBP) method. Results from batch drying processes with online measurement and feedback control are given and compared with no feedback control. To compare the operation efficiency, the thermal efficiency is considered and the results show the possibility of online control and optimisation of the fluidised bed drying processes, based on online measurement of solids moisture by ECT. Some challenges and future work are discussed.
    Chemical Engineering Science - CHEM ENG SCI. 01/2009; 64(12):2893-2902.
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    ABSTRACT: In this paper, the modeling and control of the moisture content of the particles in a batch fluidized bed dryer are studied. First, a lumped mechanistic model is developed to describe the heat and mass transfer between solid, gas and bubble phases and experimental validation shows that the model can be used to predict the particle moisture content and temperature profiles during the drying process in the bed dryer. By validating the model both with and without an insulator on the wall of the dryer, it is shown that the wall temperature has a major effect on the process. Feedback control of material moisture content in a bed dryer is studied with tomographic sensors included in the control loop. A controller is designed to achieve a desired drying rate for wet materials. Simulations show that it is possible to control the drying rate.
    American Control Conference, 2008; 07/2008
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    ABSTRACT: Mathematical modeling, computational fluid dynamics (CFD) analysis and electrical capacitance tomography (ECT) is used to develop an understanding of batch fluidized-bed drying, which is a complex air-solids, multiphase process. The mathematical model is based on a three-phase theory that describes the mass-and heat-transfer between the air and solids phases. The CFD model is based on a two-fluid model (TFM) approach, in which both phases are considered to be continuous and fully interpenetrating. The hydrodynamic parameters used to model the heat-and mass-transfer between the two phases are determined by a correlation approach, and the estimated parameters are incorporated into a user defined function (UDF) in FLUENT. The moisture diffusion in the air and solids phases is simulated using the user defined scalar (UDS) transport equation in the software package. ECT is used for the online solids concentration and moisture measurement, based on dynamic calibration. Comprehensive comparisons between results from mathematical modeling, CFD simulation and ECT measurement are presented, and are validated using experiment results. Online measurement of moisture content is compared with a static calibration. The mathematical model, CFD and ECT presented are being integrated into an online process control system for a batch fluidized-bed drying application in the pharmaceutical industry. © 2007 American Institute of Chemical Engineers AIChE J, 2008
    AIChE Journal 12/2007; 54(2):427 - 444. · 2.58 Impact Factor
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    ABSTRACT: This paper presents a mathematical model based on a three-phase theory, which is used to describe the mass and heat transfer between the gas and solids phases in a batch fluidised bed dryer. In the model, it is assumed that the dilute phase (i.e., bubble) is plug flow while the interstitial gas and the solid particles are considered as being perfectly mixed. The thermal conductivity of wet particles is modelled using a serial and parallel circuit. The moisture diffusion in wet particles was simulated using a numerical finite volume method. Applying a simplified lumped model to a single solid particle, the heat and mass transfer between the interstitial gas and solid phase is taken into account during the whole drying process as three drying rate periods: warming-up, constant rate and falling-rate. The effects of the process parameters, such as particle size, gas velocity, inlet gas temperature and relative humidity, on the moisture content of solids in the bed have been studied by numerical computation using this model. The results are in good agreement with experimental data of heat and mass transfer in fluidised bed dryers. The model will be employed for online simulation of a fluidised bed dryer and for online control.
    Chemical Engineering Science. 01/2007;
  • Y Li, W Q Yang
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    ABSTRACT: Electrical capacitance tomography (ECT) is an effective technique for elucidating the distribution of dielectric materials inside closed pipes or vessels. This paper describes a virtual electrical capacitance tomography (VECT) system, which can simulate a range of sensor and hardware configurations and material distributions. A selection of popular image reconstruction algorithms has been made available and image error and capacitance error tools enable their performance to be evaluated and compared. Series of frame-by-frame results can be stored for simulating real-time dynamic flows. The system is programmed in Matlab with DOS functions. It is convenient to use and low-cost to operate, providing an effective tool for engineering experiment.
    Journal of Physics Conference Series 08/2005; 15(1):183.
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    ABSTRACT: Electrical capacitance tomography (ECT) is regarded as a successful method for visualising cross-sectional distribution and measuring multi-phase flows (MPFs). Because of the “soft-field” nature of ECT and the non-linear relationship between electrical measurements and the permittivity of the measured material, image reconstruction for ECT is complicated. However, ECT offers some advantages over other tomography modalities, such as no radiation, rapid response, low cost, being non-intrusive and non-invasive, and the ability to withstand high temperature and high pressure. In principle, ECT can deal with the complexity of MPF measurement by explicitly deriving the component distributions at two adjacent planes along a pipeline. Images of the component distributions can be cross-correlated to obtain the velocity profile of the flow. Multiplying the component concentration and velocity profiles yields a measure of volumetric flow rate for each phase accurately. This paper covers the development of ECT for MPF metering and oil separator in the oil industry. The principal strategies and technologies that may be used to measure three-phase flows will be discussed, and the status of currently available tomography solutions will be reviewed.
    Flow Measurement and Instrumentation 04/2005; 16:145-155. · 0.97 Impact Factor
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    ABSTRACT: Gas–solids flows in the risers of circulating fluidised beds (CFBs) and cyclones exhibit complex physical behaviour, such as local backflow and recirculation. The difficulties in accurate measurement of gas–solids flows stem from various flow regimes, which exist in multi-phase flows in pipelines and vessels. It is necessary to investigate the solids’ fraction profile, flow regime identification, image reconstruction, flow acceleration and flow velocity. Electrical capacitance tomography (ECT) is regarded to be a successful technology for imaging industrial processes containing dielectric materials. ECT would help understanding of gas–particle interaction, particle–boundary interaction and the influence of gas on the solids’ flow turbulence.The first part of this paper covers some new developments in ECT, i.e., algorithms for 3D image presentation and on-line iterative image reconstruction. The second part presents a novel non-intrusive technique for measuring axial and angular velocities. Theoretical and experimental studies, carried out using cross-correlation techniques in a cyclone separator dipleg, confirm the feasibility of on-line velocity measurement. Experimental results from various gas–solids flow facilities, CFB and cyclone, are presented.
    Flow Measurement and Instrumentation - FLOW MEAS INSTRUM. 01/2005; 16(2):135-144.
  • S. Liu, L. Fu, W.Q. Yang, H.G. Wang, F. Jiang
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    ABSTRACT: Electrical capacitance tomography (ECT) has been developed for imaging dielectric material distributions. While iterative image reconstruction algorithms may produce high-quality images, they are regarded as being time-consuming and currently can only be used offline. This paper describes a new image reconstruction algorithm for ECT. First, a coefficient matrix is generated through an offline iteration process. The matrix is then used for online image reconstruction in the same way as a sensitivity map is used in the popular linear back-projection (LBP) algorithm. This new algorithm can produce similar quality images to the Landweber iteration algorithm, but at the same speed as the LBP. An optimal step-length has been incorporated into the new algorithm for improved convergence. The algorithm has been evaluated by both simulation and experiment.
    IEE Proceedings - Science Measurement and Technology 06/2004; · 0.49 Impact Factor
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    ABSTRACT: It is important to investigate the behavior of circulating fluidized beds (CFB) for efficient coal combustion. Electrical capacitance tomography (ECT) was applied to the measurement of gas/solids distribution in square CFBs. An iterative method was used to achieve improved image reconstruction over the commonly used linear back-projection algorithm. The solids concentration profile, temporal variation of average solids concentration, and frequency spectra, which were obtained from the ECT data, are presented.
    AIChE Journal 04/2004; 48(8):1631 - 1638. · 2.58 Impact Factor
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    ABSTRACT: Electrical capacitance tomography (ECT) has been under rapid development in recent years. However, as a relatively new technology, ECT is far from mature and its applications are rather appliance-dependent, i.e. the sensor design, calibration, and data interpretation etc., depend on the understanding of the specific situations for ECT measurement. The authors have experimented several sensing strategies and developed algorithms for 3D image presentation and online iterative image reconstruction, and applied ECT to the measurement of several typical cases of two phase flows, which is reported in this paper.
    ASME 7th Biennial Conference on Engineering Systems Design and Analysis; 01/2004
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    ABSTRACT: A highly sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multi-phase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10−17 F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20–95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the form of liquid droplets were detectable. It has also been shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.
    Flow Measurement and Instrumentation. 01/2004;
  • W.Q. Yang, A.L. Stott, J.C. Gamio
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    ABSTRACT: An ac-based capacitance transducer has been designed for use in electrical capacitance tomography (ECT) systems. The stray capacitance between the measurement electrodes and earth can be relatively large and may affect the performance of the transducer. This paper analyzes this effect, taking into account the ON-resistance of the CMOS switches in the circuit, the finite gain of op-amps and gain errors in the detection measuring unit, so that the overall measurement error can be estimated. It is shown that if the stray capacitance varies between 90 and 210 pF, the measurement error would be between +0.03% to -0.1%. This is negligibly small for ECT applications, confirming that this ac-based capacitance transducer is effectively stray-immune.
    IEEE Transactions on Instrumentation and Measurement 11/2003; · 1.71 Impact Factor
  • W. Q. Yang, Lihui Peng
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    ABSTRACT: Electrical capacitance tomography (ECT) is used to image cross-sections of industrial processes containing dielectric material. This technique has been under development for more than a decade. The task of image reconstruction for ECT is to determine the permittivity distribution and hence material distribution over the cross-section from capacitance measurements. There are three principal difficulties with image reconstruction for ECT: (1) the relationship between the permittivity distribution and capacitance is non-linear and the electric field is distorted by the material present, the so-called 'soft-field' effect; (2) the number of independent measurements is limited, leading to an under-determined problem and (3) the inverse problem is ill posed and ill conditioned, making the solution sensitive to measurement errors and noise. Regularization methods are needed to treat this ill-posedness. This paper reviews existing image reconstruction algorithms for ECT, including linear back-projection, singular value decomposition, Tikhonov regularization, Newton-Raphson, iterative Tikhonov, the steepest descent method, Landweber iteration, the conjugate gradient method, algebraic reconstruction techniques, simultaneous iterative reconstruction techniques and model-based reconstruction. Some of these algorithms are examined by simulation and experiment for typical permittivity distributions. Future developments in image reconstruction for ECT are discussed.
    Measurement Science and Technology 01/2003; 14(1). · 1.44 Impact Factor
  • J C Gamio, W Q Yang, A L Stott
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    ABSTRACT: An ac-based capacitance transducer has been designed for use in electrical capacitance tomography systems. It has a high signal-to-noise ratio and good stray-immunity, compared with a charge/discharge transducer designed for the same purpose. However, the non-ideal characteristics of amplifiers and CMOS switches limit the performance of the ac-based transducer. This paper analyses the effects of the frequency-dependent gain of the amplifiers and the finite `on' resistance of the CMOS switches. It is shown that the non-ideal characteristics restrict the frequency response of the transducer by introducing extra poles, which depend not only on the parameters of the devices but also on the stray capacitance. Mathematical expressions quantifying these effects are presented.
    Measurement Science and Technology 07/2001; 12(8):1076. · 1.44 Impact Factor
  • S Liu, W Q Yang, H Wang, F Jiang, Y Su
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    ABSTRACT: The fluidization conditions in a fluidized bed can vary dramatically, from bubbling to circulating fluidization. Considering the dielectric properties and the rapid movement of the solids in fluidized beds, electrical capacitance tomography (ECT) is particularly suitable for measuring the concentration and distribution of solids in fluidized beds. This paper reports the use of a square ECT sensor to investigate the behaviour of fluidized beds, showing the unique advantages of using ECT in measuring cross-sectional concentration profiles of solids. Different fluidization regimes manifest different characteristics, in terms of the concentration distribution of solids.
    Measurement Science and Technology 07/2001; 12(8):1120. · 1.44 Impact Factor
  • S. Liu, W. Q. Yang, H. Wang, G. Yan, Z. Pan
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    ABSTRACT: Electrical capacitance tomography (ECT) was applied in measuring solids distribution in square circulating fluidized beds. The fluidization conditions varied from bubbling fluidized bed to circulating fluidized bed. In the whole range of fluidization conditions, ECT was able to instantaneously provide the solids concentration and voids distributions in the fluidized beds. According to the acquired data from ECT and reconstructed image, different fluidization regimes can also be identified.
    Journal of Thermal Science 04/2001; 10(2):176-181. · 0.30 Impact Factor
  • Shi Liu, W. Q. Yang, H. G. Wang
    Intelligent Systems and Smart Manufacturing; 02/2001

Publication Stats

678 Citations
30.78 Total Impact Points

Institutions

  • 2005–2010
    • The University of Manchester
      • School of Electrical and Electronic Engineering
      Manchester, ENG, United Kingdom
  • 2008
    • University of Oxford
      • Department of Engineering Science
      Oxford, ENG, United Kingdom
  • 2000
    • Chinese Academy of Sciences
      • Institute of Engineering Thermophysics
      Peping, Beijing, China