Electrical Capacitance Tomography Sensor Research Articles

DEVELOPMENT OF IMAGE RECONSTRUCTION FOR DETECTING STATIC OIL-GAS REGIMES USING INVASIVE ELECTRICAL CAPACITANCE TOMOGRAPHY IN STEEL PIPE APPLICATION – AN INITIAL STUDY An Initial Study

Electrical Capacitance Tomography (ECT) is a well-known technique for identifying two-phase regimes when a non-conducting medium is the main medium inside a pipe. However, the common non-invasive techniques of ECT are not suitable for monitoring non-conducting systems that use steel pipes. This is because the placement of the common ECT sensor is outside of the pipe and thus cannot penetrate the conducting pipe. Therefore, this paper presents the development of image reconstruction techniques for invasive Electrical Capacitance Tomography (ECT) in steel pipe applications. The study uses eight electrodes for invasive ECT that are independently designed for easy replacement. The shield guard of each electrode is individually designed, unlike the common sensor of ECT. Moreover, it produces a sensitivity map in the forward problem by modeling the geometry to mimic the real hardware of invasive ECT in Comsol Multiphysics livelink with MATLAB. The data from real hardware is exported offline and a linear back projection algorithm is used as the inverse problem. The phantom of gas-oil with different sizes, positions, and multiple phantoms from the range of 20mm, 25 mm and 33mm are tested. The tomograms of the region of interest can be obtained as a result. The paper concludes that the developed image reconstruction techniques for invasive ECT in steel pipe applications can provide acceptable and reliable results. This study can be useful for researchers and practitioners in the field of ECT and steel pipe applications.

Dual-plane miniature planar 3D ECT sensor based on 3 × 3 matrix electrode array

PurposeAs one of the tomographic imaging techniques, electrical capacitance tomography (ECT) is widely used in many industrial applications. While most ECT sensors have electrodes placed around a cylindrical chamber, the planar ECT sensor has been investigated for depth and defect detection. However, the planar ECT sensor has limited height and depth sensing capability due to its single-sided assessment with the use of only a single-plane design. The purpose of this paper is to investigate a dual-plane miniature planar 3D ECT sensor design using the 3 × 3 matrix electrode array.Design/methodology/approachThe sensitivity map of dual-plane miniature planar 3D ECT sensor was analysed using 3D visualisation, the singular value decomposition and the axial resolution analysis. Then, the sensor was fabricated for performance analysis based on 3D imaging experiments.FindingsThe sensitivity map analysis showed that the dual-plane miniature planar 3D ECT sensor has enhanced the height sensing capability, and it is less ill-posed in 3D image reconstruction. The dual-plane miniature planar 3D ECT sensor showed a 28% improvement in reconstructed 3D image quality as compared to the single-plane sensor set-up.Originality/valueThe 3 × 3 matrix electrode array has been proposed to use only the necessary electrode pair combinations for image reconstruction. Besides, the increase in number of electrodes from the dual-plane sensor setup improved the height reconstruction of the test sample.

Study on the relation of bubble behavior and bed density in gas–solid separation fluidized bed using electrical capacitance tomography

Gas–solid Fluidized bed technology has a pivotal role in coal separation. Bubble movement behavior is an important factor affecting the fluidization stability. Fluidized bed measurement is an essential link in the bubble behavior study. As the main evaluation parameters, the concentration distribution and density distribution can reflect the bubble movement behavior. This work uses a noninvasive method of electrical capacitance tomography (ECT) for fluidized bed measurements, combined with COMSOL simulation validation for real-time imaging of bubbles in Geldart Group B magnetite powder particles. Meanwhile, the most suitable reconstruction algorithm for gas–solid separation fluidized bed is selected from three image reconstruction algorithms. And then concentration distribution and density distribution are analyzed. The results show that under reasonable gas velocity conditions (U–U mf =2.28 and 3.17 cm/s), the central region ([0, 1/4]) concentrations of [0.43–0.45] and [0.39–0.42] and densities of [1.98–2.06 g/cm3] and [1.86–1.96 g/cm3] are obtained by ECT measurements, respectively. Finally, the bed density obtained from the ECT sensors in the experiment was validated using three different bed density models. The error can be controlled to within 20%, which indicates that the ECT measurement method has a fairly high reliability and accuracy in dry coal beneficiation field.

Miniature planar 3D ECT sensor based on distributed electrode arrangement

Due to the low sensitivity in the middle of sensing chamber of planar peripheral electrode arrangement tomography system, a miniature planar electrical capacitance tomography (ECT) sensor with distributed electrode arrangement is proposed for imaging of 3D cultivated cells. In this work, the 3D imaging capability of the proposed sensor was compared to the peripheral electrode arrangement ECT sensor through numerical simulation of the sensitivity maps. The analysis of the sensitivity maps revealed that the sensitivity distribution of proposed sensor covered the entire surface of the sensing chamber which indicated improved sensitivity coverage in the sensing chamber. In addition, the axial resolution and the singular value decomposition (SVD) analysis of the sensitivity maps demonstrated that the proposed sensor has better 3D imaging capability. Then, the proposed sensor composed of nine electrodes, a thin PDMS layer and a glass coverslip was fabricated and investigated. The experimental results showed that the reconstructed 3D image by the proposed sensor was consistent at all the test positions. In contrast to the planar peripheral electrode arrangement ECT sensor that has an average correlation coefficient (CC) of 0.4571, the proposed sensor achieved a higher average CC of 0.5454, indicating better 3D imaging performance.

A 12-Electrode ECT Sensor with Radial Screen for Fluid Diagnosis

In this paper, the use of radial screens in an Electrical Capacitance Tomography (ECT) sensor is investigated with the aim of resulting in higher-resolution images. The effect of the screens on the quality of the reconstructed images was simulated. 12-electrode ECT sensors with and without screens were designed and tested. The capacitance between different electrode pairs was measured for two permittivity distributions. The obtained capacitance data were used to reconstruct images using the Projected Landweber Iteration algorithm based on linear and semi-linear ECT models. The sensitivity of the measurements and the accuracy of the obtained images for the ECT sensors with and without screens were analyzed. The main conclusion is that a little improvement in the quality of images can be achieved with the use of 12-Electrode ECT sensors with radial screen.

Diagnosis of Two-Phase Oil/Gas Flow in a Closed Pipe using an 8-Electrode ECT System

Electrical tomography techniques have been developed to monitor the internal behavior of industrial processes. Electrical capacitance gives the best benefits over other tomography modalities, as it has no radiation, is non-intrusive, and has a low cost. This study investigated the diagnosis of two-phase oil/gas flow in a closed pipe, using an image data capture system for an 8 external electrode Electrical Capacitance Tomography (ECT) sensor. The system had a high-resolution ratio, a small measurement error, and was able to remove the effects of stray capacitance. Experimental measurements were carried out on two different materials that filled the space inside the pipe in different proportions to determine the sensitivity and accuracy of the measurement. The results showed that the system had fast image data capture time, high accuracy, a very small resolution ratio, and a good signal-to-noise ratio and quality factor.

Investigation of wetting and drying process in a spout-fluid bed using acoustic sensor and electrical capacitance tomography

To investigate complex gas-solids flow characteristics of a spout-fluid bed with bafflers in wetting and drying process, a non-intrusive measurement technique combining pressure, acoustic transmitters and an electrical capacitance tomography (ECT) sensor is proposed in this paper. The proposed approach can collect acoustic and pressure signals and realize visualization in three flow regions separated by two bafflers synchronously. By ECT images and power spectrum and wavelet analysis of the pressure drop signals, two typical flow state transitions in the wetting and drying process can be identified. The result analysis based on acoustic transmitter indicates that the particle–wall collision frequency band is narrow and the particle–particle collision frequency band is wide. A key recurrence quantization parameter of acoustic signal, Laminarity, increases with the decrease of particle flowability. The parameter of Laminarity combined with the capacitance signal related to the particle moisture content can effectively reflect the wetting rate and provide an accurate monitoring of de-fluidization process in the bed.

Capacitance Estimation for Electrical Capacitance Tomography Sensors Using Digital Processing of Time-Domain Voltage Response to Single-Pulse Excitation

In this paper, a new approach for capacitance measurement for electrical capacitance tomography (ECT) sensors is proposed. The method is based on the digital processing of the time-domain voltage measurements at the sensor electrodes. Furthermore, a robust capacitance estimation algorithm is developed to convert the measured voltage time-series to inter-electrode capacitances. The proposed measurement technique simplifies the electronic design of the ECT sensor and is suitable for use in applications requiring a compact device with a fast scan time. The accuracy and sensitivity of the method are investigated numerically and experimentally using a prototype sensor. In particular, the sensitivity of the estimated capacitance to measurement noise levels is analyzed in detail. Additionally, an analysis of the parameters that affect the accuracy of estimated capacitances is carried out from which we are able to demonstrate that the method is immune to effects such as stray capacitances between the electrodes and the ground. A prototype sensor with an open curved geometry on a millimeter scale is used to test the method empirically. Experimental results obtained for measurements with mineral oil and water are shown and compared against capacitances obtained using a physics-based forward model of the sensor. The inter-electrode capacitances in the range of tens of femtofarads to a few picofarads are estimated and a close match with the forward model results is obtained.

Study of Fluidization Behavior Transition from Geldart B to A Induced by High Temperature Using Electrical Capacitance Tomography

The transition of the fluidization behavior of Geldart B particles to that of A particles induced by temperature change was investigated by a developed high-temperature electrical capacitance tomography (ECT) sensor. Silica particles with a Sauter mean diameter of 237 μm and density of 2650 kg/m3, typically Geldart B particles under ambient conditions, were fluidized in a column of 5.5 cm from 20 to 600 °C. With the increase in temperature, ECT measurements showed a decrease in minimum bubbling velocity (Umb), no bed expansion characteristic in the homogeneous fluidization regime, an absence of multiple-bubbles regime, and a larger bubble size. The pressure drop against superficial gas velocity curves at elevated temperatures confirmed homogeneous fluidization between the minimum fluidization velocity (Umf) and Umb. Our analysis demonstrates that cohesive interparticle forces, which increase linearly with temperature, are responsible for the fluidization behavior transition of the silica particles.

Robot sensing based on electrical capacitance tomography sensor with rotation

The existing sensing technology for industrial robot hands cannot sense inside of an object. To recognise the material and internal distribution of an object when it is grasped, electrical capacitance tomography (ECT) may be used if the object is non-conductive, as ECT can measure the permittivity distribution inside an object from external capacitance measurements. An ECT sensor normally has 8 or 12 electrodes equally distributed around an object. This paper introduces the first attempt to make use of ECT with robot hands. Because the number of electrodes is limited, it is necessary to rotate the object to be imaged mechanically, so that sufficient measurements can be taken. Four aspects of the ECT sensor are discussed based on simulation: (1) the structure of electrodes; (2) the number of rotation times; (3) the starting position of rotation; and (4) the diameter of rotation. Two image reconstruction algorithms are used: the linear-back projection and Landweber iteration with three typical distributions. The results show that the rotational three-electrode ECT structure has good ability to produce useful images, showing the internal distribution of unknown objects.

Electrical Capacitance Tomography-Based Flow Measurement in a Closed Container Using 16-Electrode Sensor in Contrast with 8-Pair-16-Electrodes Topology

Electrical Capacitance Tomography (ECT) is a commonly used technique to investigate the interior of a pipe by evaluating the coupling capacitances of a multi-electrode assembly. In this article, to improve the performance of the ECT sensor, sesitivity matrix, and hence the image quality, a typical customized 16-to-8 electrode ECT sensor is proposed, designed, simulated, and implemented in parallel with a standard 16-electrode ECT sensor. The results of both types of sensors are noted and compared to each other. It is evident from the results obtained during this experiment that the performance of the customized 16-8 electrode ECT sensor is comparatively better and exhibits better quality in its image reconstruction. The percentage of accuracy for the image quality could also be appreciated as compared with the standard 16-electrode ECT sensor. Further, a test was conducted for both the sensors under similar specifications and conditions to measure the flow of water, and it was found from the images that, for the same flow speed, image clarity is better for the customized 16-8 electrode ECT sensor in comparison with the standard 16-electrode ECT sensor. These findings may be useful for real time applications in the process industry.

Flow pattern identification for gas-oil two-phase flow based on a virtual capacitance tomography sensor and numerical simulation

Gas-oil two-phase flow is widely encountered in oil exploitation and transportation pipelines. It's complex and transient changes of flow regimes present a great challenge for accurate and real-time measurement. As a non-invasion and real-time measuring method, electrical capacitance tomography (ECT) is suitable for the transient measurement of non-conductive gas-oil flow. However, the highly random and nonlinear nature of multiphase flow make it difficult and limited to investigate the flow parameters based on either static or dynamic measurement. In this research, the whole process of dynamic measurement of ECT applying in gas-oil two-phase flow is thoroughly studied, including simulation calculation, experimental validation and comprehensive data analysis. A simulation approach by coupling the flow and electrostatic field is proposed based on a virtual ECT sensor, in order to monitor the gas-oil two-phase flow characteristics. Based on FLUENT and COMSOL platform, the numerical simulation under six typical flow patterns in a horizontal pipe is carried out. Combining the visualized image generated by ECT measurement and the theory of flow pattern transition, the formation mechanism and structural characteristics of different gas-oil flow patterns are analyzed in detail. Furthermore, this research attempts to analyze the signal fluctuation characteristics caused by flow pattern change, in order to access more in-depth flow information implied in the original capacitance data, via time-series analysis as well as frequency domain analysis based on Flourier Transform. At last, a series of dynamic experiment is conducted to verify the feasibility of the simulation and data analysis approach. The experiment focuses on the flow pattern transition, gas-liquid dynamic characteristics and noise influence in the actual process. It can be concluded from the results of simulation and experiment tests, combining the visualized images and the dynamic characteristics of capacitance signals can make it more effective and intuitive for flow pattern identification, which might be used for the online measurement in real-industry process.

Multiphase Flowrate Measurement With Multimodal Sensors and Temporal Convolutional Network

Accurate multiphase flow measurement is vital in monitoring and optimizing various production processes. Deep learning has as of late arose as a promising approach for assessing multiphase flowrate dependent on various customary flow meters. In this paper, we propose a multi-modal sensor and Temporal Convolution Network (TCN) based method to predict the volumetric flowrate of oil/gas two-phase flows. The volumetric flowrates of the liquid and gas phase vary from 0.96 - 6.13 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{{3}}$ </tex-math></inline-formula> /h and 5.5 - 121.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{{3}}$ </tex-math></inline-formula> /h, respectively. The multi-modal sequential sensing data are simultaneously collected from a Venturi tube and a dual-plane Electrical Capacitance Tomography (ECT) sensor in a pilot-scale multiphase phase flow facility. The reference data are derived from the single-phase flowmeters. Z-score and First-Difference (FD) data pre-processing methods are employed to manipulate the collected instantaneous time series multi-modal sensing data. The pre-processed data are utilized for training the TCN model. Experimental results reveal that the TCN model can effectively predict the multiphase flowrate based on the multi-modal sensing data. The results provide guidance on data pre-processing methods for multiphase flowrate estimation and demonstrate the effectiveness of combining multi-modal sensors and TCN for multiphase flowrate prediction under complex flow conditions.

Measurement of Transient Flash Evaporation Flow in Liquefied Gas Propulsion Using Dual-Plane ECT

In this paper, the transient flash evaporation flow in liquified gas propulsion (LGP) was measured using a dual-plane electrical capacitance tomography (ECT) sensor. The novelty mainly stems from a selection method for more accurate liquid holdup measurement, a constrained adaptive cross-correlation algorithm for more stable velocity, and compensation methods against the changes of temperature and pressure. By the selection method, inter-electrodes capacitances that contribute less to the flow measurement, are removed from each data frame and more accurate liquid holdup is derived via image reconstruction. The adaptive cross-correlation algorithm with a constraint on the correlation coefficient is adopted to alleviate the adverse effect of the fast changes of flow pattern on the velocity measurement. Then, the compensation methods are realized by correcting the deviations of phase density and permittivity caused by dramatic temperature and pressures changes. Simulations and experiments validated the effectiveness of the proposed methods to derive the mass flow rate of the two-phase flow via the measured liquid holdup, flow velocity and estimated phase density. It is shown that the remaining mass of propellant in the storage tank calculated from the mass flow rate is in good agreement with the measured reference by the electronic balance, where the average relative errors under different initial pressures are less than 10%. As the best of our knowledge, this is the first-time of transient flash evaporation flow measurement in a lab-built LGP device, which is promising to be applied for the effective online control to maximize the output impulse of LGP and estimate the remaining life of small spacecrafts.

Multifocus Image Reconstruction and Fusion for 3-D Flow Visualization Using an Optimized Four-Plane ECT Sensor

3D image reconstruction of permittivity distribution is very challenging for electrical capacitance tomography (ECT) because of the limited number of capacitance measurements and the non-uniformly distributed sensitivity, especially for axial distribution. In this paper, a 3D image reconstruction method based on fuzzy adaptive Kalman filter (FAKaF) and multi-focus image fusion is used to improve the 3D image quality. A four-plane ECT sensor is constructed and optimized based on the conformal transformation method, whose sensitivity in the imaging volume is more uniform in the axial direction. Then a FAKaF is established to obtain a series of initial reconstructed images with higher image quality in the central region, which can be seen as a sequence of multi-focus 3D images. Finally, an image registration and fusion method based on cross correlation and spatial frequency is used to extract and fuse the high-quality parts of each image in the sequence to further improve the quality of the reconstructed images. Simulations and experiments were carried out to evaluate the performance of the proposed method. The results show that compared with the widely-used methods, initial images reconstructed using the proposed FAKaF-based method possess higher image quality. Through image fusion, higher correlation coefficients between reference distributions and fused images can be obtained, proving the effectiveness of the proposed method.

On-line monitoring of flow process in a spout-fluid bed by combining electrical tomography and high-speed CCD camera

To investigate spouted flow characteristics in a rectangular spout-fluid bed with bafflers, a non-intrusive measurement approach, which combines electrical capacitance tomography (ECT), pressure measurements and high-speed CCD imaging technology, is proposed. The ECT sensor has 12 electrodes on the external wall and 12 electrodes inside, forming three imaging regions with 8 electrodes in each region. The flow hydrodynamic characteristics in the spouted bed e.g., pressure fluctuation, particle packing fraction and fountain form, are investigated. The frequency domain of pressure and particle packing fraction signals as well as ECT images indicate that the flow regime in the jet region transits from slugging to spouting in fountain formation process, and when the fluidization velocity in one side increases, the flow regime in the same region transits into slugging bed. The spouting pressure drop is affected by the fluidization condition in the side region, and the high characteristic frequency of pressure signal decreases when the side region condition changes from blockage to fluidization. The fountain height increases linearly with the superficial gas velocity. When the gas velocity is high, the fountain tends to be offset by the influence of the lateral airflow which is caused by the imbalance of the air pressure on two side regions.

Preliminary study of CO2 frost formation during cryogenic carbon capture using tomography analysis

Cryogenic carbon capture (CCC) is a potential technological solution to reduce CO2 emissions and achieve the needed environmental targets. CCC provides a relatively compact solution to industries where more mature technologies would have difficulty scaling down economically. However, there is a lack of research on frost formation of CO2 within packed bed systems, despite the influence of the CO2 frost layer on thermal conductivity leading to excessive cooling costs. Understanding the rate of CO2 frost growth and accumulation within a packed bed is critical to the design of the capture column. Therefore, real-time quantitative imaging becomes increasingly desirable to study the CO2 frost formation during cryogenic carbon capture, but it may be difficult by most of the traditional measurement methods. This study aims to investigate the use of an Electrical Capacitance Tomography (ECT) to monitor the real-time CO2 frost formation in a fixed packed bed. In this work, the evolution of the permittivity distribution during the capture process has been investigated in detail by experiments, elucidating the effect of the bed material type and bed material temperature. An ECT sensor was constructed to measure frost distribution to elucidate the mechanisms of CO2 frost formation by first testing on ice frost in the packed bed. The ECT images of ice formation were reconstructed by measurement data with a conventional algorithm. The results show that ECT could effectively monitor the changes of relative permittivity caused by the frost formation in real-time. With the help of an image reconstruction algorithm, the outline and position of the permittivity change area can be monitored. These results indicate that ECT has the potential to be a novel technique for monitoring CO2 frost formation during cryogenic carbon capture.

Image Processing and Measurement of the Bubble Properties in a Bubbling Fluidized Bed Reactor

The efficiency of a fluidized bed reactor depends on the bed fluid dynamic behavior, which is significantly influenced by the bubble properties. This work investigates the bubble properties of a bubbling fluidized bed reactor using computational particle fluid dynamic (CPFD) simulations and electrical capacitance tomography (ECT) measurements. The two-dimensional images (along the reactor horizontal and vertical planes) of the fluidized bed are obtained from the CPFD simulations at different operating conditions. The CPFD model was developed in a commercial CPFD software Barracuda Virtual Reactor 20.0.1. The bubble behavior and bed fluidization behavior are characterized form the bubble properties: average bubble diameter, bubble rise velocity, and bubble frequency. The bubble properties were determined by processing the extracted images with script developed in MATLAB. The CPFD simulation results are compared with experimental data (obtained from the ECT sensors) and correlations in the literature. The results from the CPFD model and experimental measurement depicted that the average bubble diameter increased with an increase in superficial gas velocities up to 4.2 Umf and decreased with a further increase in gas velocities due to the onset of large bubbles (potential slugging regime). The bubble rise velocity increased as it moved from the lower region to the bed surface. The Fourier transform of the transient solid volume fraction illustrated that multiple bubbles pass the plane with varying amplitude and frequency in the range of 1–6 Hz. Further, the bubble frequency increased with an increase in superficial gas velocity up to 2.5Umf and decreased with a further increase in gas velocity. The CPFD model and method employed in this work can be useful for studying the influence of bubble properties on conversion efficiency of a gasification reactor operating at high temperatures.

A Measurement Compensation Method for Electrical Capacitance Tomography Sensors with Inhomogeneous Electrode Parameters

An electrical capacitance tomography (ECT) sensor is an array capacitive sensor that is sensitive to the medium of the measured object and can be widely used in oil, natural gas, machinery and other industrial fields to solve the problem of multiphase fluid object parameter detection in industrial processes. However, ECT sensor uniformity defects need to be addressed. Aiming at the problem that the non-uniform electrode spacing angle affects the characteristics of the measured value of the actual ECT sensor, a method for compensating the measured value of the ECT sensor based on the assumption that the geometric factor is invariant is proposed. The simulated measurement value in the case of the tube and the measurement value of the actual sensor in the case of an empty tube and a full tube are to compensate the measurement value of the actual ECT. Experiments show that, without compensation, non-ideal sensor monitoring has large error, and, after compensation, it has a good effect and can be expected to perform satisfactorily in practical use.

Tomography-assisted control for the microwave drying process of polymer foams

This paper presents the integration of electrical capacitance tomography (ECT) with a moisture controller for the microwave drying of polymer foam. The proportional–integral (PI) control and the linear quadratic Gaussian (LQG) control are employed in designing the controller. The control objective in this process is that the moisture of polymer foam after the drying process reaches the desired set point. The permittivity distribution of polymer foam after the drying process is estimated in real-time using a designed ECT sensor and transferred as feedback to the controller. Since the permittivity and the moisture are strongly correlated, the material moisture can be controlled by controlling the permittivity. A state-space model is derived for the microwave drying process based on a system identification approach using the experimental data from the process. The derived model is employed in designing the LQG controller and adjusting the parameters of the PI controller. The designed controllers are implemented on a testbed microwave oven, and the experimental results show that the designed controllers are able to follow the desired set point moisture. The performance of the system with both controllers is compared, and their advantages and disadvantages are discussed. Moreover, the benefits of having a moisture controller for the microwave drying process are shown in simulation studies compared to an uncontrolled system.