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The aim of this research is to investigate the unique shape (concentric-annulus) electrical capacitance tomography (ECT) sensors. This is motivated by the desire to improve the contrast and spatial resolution of the images reconstructed using ECT sensors with internal-external electrodes (IEEs). Both numerical simulation and experimental study were carried out with the goal of providing an improved understanding of the configuration of IEE sensors, the internal shield and the measurement strategies. Simulation results are in agreement with the experimental results. Using the linear back projection algorithm, the IEE sensor with 12 external electrodes and 4 internal electrodes with the external-opposite-internal measurement strategy can reconstruct high-quality images. In experimental studies, the internal shield may reduce the quality of capacitance measured from the internal electrodes. [ABSTRACT FROM AUTHOR]

To optimize the design and operation of a pressurised circulating fluidised bed (PCFB) system, it is necessary to understand the gas–solid flow characteristics and properly measure the solid circulation flux in the cyclone dipleg and loop-seal of the PCFB. In this research, electrical capacitance tomography (ECT) measurement and computational particle fluid dynamic (CPFD) simulation are combined to investigate the multiphase flow behaviour of a ‘cold’ PCFB, in particular the cyclone dipleg. A dual-plane ECT sensor is used for visualisation and online monitoring of the particle distribution. The particle velocity is measured by cross-correlation of two signals from capacitance electrodes, and the circulation flux is analysed. In addition, 3D full-loop CPFD simulation incorporating an energy-minimization multi-scale (EMMS) drag model is performed on a Barracuda platform, to understand the gas–solid hydrodynamic behaviour, validate and supplement the experimental measurements. The results show that the CPFD prediction agrees well with the ECT measurement in terms of the particle volume fraction distribution, velocity and circulation flux. The time-averaged gas–solid flow behaviour, instantaneous hydrodynamic features and the effects of operating pressure on particle distribution and the flow regime in the PCFB dipleg are unravelled. This is the first investigation of a solid circulation flux measurement in the cyclone dipleg and loop-seal of a PCFB system using a combination of ECT measurements, cross-correlation and CPFD simulation with high-pressure operational conditions. [ABSTRACT FROM AUTHOR]

Normally, a gas–solids flow should be non-conductive. With the increase in moisture content in a gas–solids flow, the non-conductive flow may become low-conductive. For the measurement of low-conductive materials, i.e. particles with high moisture content, in the pharmaceutical industry, both electrical capacitance tomography (ECT) and traditional electrical resistance tomography driven by current (ERTc) generate poor images. An ERT driven by voltage (ERTv) may be suitable for the measurement of materials with low-conductivity. In this research, ERTv is used for the measurement of a wet gas–solids flow with different moisture content and different flow patterns, as well as a gas–liquid flow with different flow patterns. In the meantime, ECT is also used for the same flow conditions for comparison. The measurement results of ERTv and ECT are evaluated by the correlation coefficient. The results show that ERTv is good for measurement of a gas–solids flow with high moisture content and a gas–liquid flow when the conductivity of the continuous phase is low or moderate, while ECT is suitable for the measurement of a dry gas–solids flow. [ABSTRACT FROM AUTHOR]

In the design of electrical capacitance tomography (ECT) sensors, the internal wall thickness can vary with specific applications, and it is a key factor that influences the sensitivity distribution and image quality. This paper will discuss the effect of the wall thickness of ECT sensors on image quality. Three flow patterns are simulated for wall thicknesses of 2.5 mm to 15 mm on eight-electrode ECT sensors. The sensitivity distributions and potential distributions are compared for different wall thicknesses. Linear back-projection and Landweber iteration algorithms are used for image reconstruction. Relative image error and correlation coefficients are used for image evaluation using both simulation and experimental data. [ABSTRACT FROM AUTHOR]

Electrical capacitance tomography (ECT) is an imaging technique for measuring the permittivity change of materials. Using a multi-plane ECT sensor, three-dimensional (3D) distribution of permittivity may be represented. In this paper, three excitation strategies, including single-electrode excitation, dual-electrode excitation in the same plane, and dual-electrode excitation in different planes are investigated by numerical simulation and experiment for two three-plane ECT sensors with 12 electrodes in total. In one sensor, the electrodes on the middle plane are in line with the others. In the other sensor, they are rotated 45° with reference to the other two planes. A linear back projection algorithm is used to reconstruct the images and a correlation coefficient is used to evaluate the image quality. The capacitance data and sensitivity distribution with each measurement strategy and sensor model are analyzed. Based on simulation and experimental results using noise-free and noisy capacitance data, the performance of the three strategies is evaluated. [ABSTRACT FROM AUTHOR]

The hydrodynamics of gas–solids flow in the bottom of a circulating fluidized bed (CFB) are complicated. Three-dimensional (3D) electrical capacitance tomography (ECT) has been used to investigate the hydrodynamics in risers of different shapes. Four different ECT sensors with 12 electrodes each are designed according to the dimension of risers, including two circular ECT sensors, a square ECT sensor and a rectangular ECT sensor. The electrodes are evenly arranged in three planes to obtain capacitance in different heights and to reconstruct the 3D images by linear back projection (LBP) algorithm. Experiments were carried out on the four risers using sands as the solids material. The capacitance and differential pressure are measured under the gas superficial velocity from 0.6 m s−1 to 3.0 m s−1 with a step of 0.2 m s−1. The flow regime is investigated according to the solids concentration and differential pressure. The dynamic property of bubbling flows is analyzed theoretically and the performance of the 3D ECT sensors is evaluated. The experimental results show that 3D ECT can be used in the CFB with different risers to predict the hydrodynamics of gas–solids bubbling flows. [ABSTRACT FROM AUTHOR]

Electrical capacitance tomography (ECT) is based on capacitance measurements from electrode pairs mounted outside of a pipe or vessel. The structure of ECT sensors is vital to image quality. In this paper, issues with the number of electrodes and the electrode covering ratio for complex liquid–solids flows in a rotating device are investigated based on a new coupling simulation model. The number of electrodes is increased from 4 to 32 while the electrode covering ratio is changed from 0.1 to 0.9. Using the coupling simulation method, real permittivity distributions and the corresponding capacitance data at 0, 0.5, 1, 2, 3, 5, and 8 s with a rotation speed of 96 rotations per minute (rpm) are collected. Linear back projection (LBP) and Landweber iteration algorithms are used for image reconstruction. The quality of reconstructed images is evaluated by correlation coefficient compared with the real permittivity distributions obtained from the coupling simulation. The sensitivity for each sensor is analyzed and compared with the correlation coefficient. The capacitance data with a range of signal-to-noise ratios (SNRs) of 45, 50, 55 and 60 dB are generated to evaluate the effect of data noise on the performance of ECT sensors. Furthermore, the SNRs of experimental data are analyzed for a stationary pipe with permittivity distribution. Based on the coupling simulation, 16-electrode ECT sensors are recommended to achieve good image quality. [ABSTRACT FROM AUTHOR]

Choosing the number of electrodes is crucial for a multi-plane electrical capacitance tomography (ECT) sensor to obtain satisfactory capacitance data and good image quality. In this paper, issues with the number of electrodes in three-plane ECT sensors are discussed. The number of electrodes on each plane for the three sensors is 4, 8, and 12, respectively. Three quality measures of resolution matrix, i.e. the amplitude response, relative position error, and spatial resolution, are defined and used for evaluating the preliminary performance of ECT sensors. Based on numerical simulation, the noise-free and noisy capacitance data obtained from the three sensors are used for image reconstruction by linear back projection (LBP) and Landweber iteration algorithms. The image quality is evaluated quantitatively in terms of image error and correlation coefficient. Based on static experiment, the effect of the number of electrodes on the quality of the capacitance data and reconstructed images is also analyzed. According to the numerical simulation and experiment results, the selection of the number of electrodes under different conditions is suggested. [ABSTRACT FROM AUTHOR]

The structure of electrodes in a multi-plane electrical capacitance tomography (ECT) sensor is vital for obtaining high-quality capacitance measurements and good images. In this paper, issues with the relative position of electrodes on each plane in three-plane ECT sensors are discussed. Five ECT sensors with different structures are compared by numerical simulation. For the five sensors, the electrodes on the second and third planes are arranged with rotation angles of 0° and 0°, 0° and 15°, 0° and 30°, 0° and 45°, and 22.5° and 45°, respectively, relative to the electrodes on the first plane. The capacitance data obtained from different sensors by numerical simulation are used for image reconstruction using linear back projection and Landweber iteration algorithms. The image quality is evaluated quantitatively in terms of image error. The sensitivity distributions of all the ECT sensors are compared. The effect of the rotation angles of electrodes on the stability of measured capacitance and on the image quality is also evaluated by experiment. The main conclusion is that the electrodes with no rotation angle should be chosen. [ABSTRACT FROM AUTHOR]

To improve the image quality and reduce the computational cost for electrical capacitance tomography (ECT), a sparsity reconstruction algorithm based on a modified Landweber iteration is presented in this paper. A soft-thresholding function is constructed for permittivity distributions with a continuous phase of low and high permittivity, respectively. An optimal step length is used during the iterative image reconstruction process. The effect of the regularization parameter, the noise level in data, and the permittivity distribution on the performance of the proposed algorithm is discussed according to the correlation coefficient. The modified Landweber iteration with a zero regularization parameter is also implemented for comparison. Simulation and experimental studies were carried out and the corresponding computational costs were estimated, showing the sparsity reconstruction outperforms the Landweber iteration. [ABSTRACT FROM AUTHOR]