Electrical Capacitance Volume Tomography Sensors Research Articles

Axial behavior of slugging flow in a gas–solid CFB riser using distributed ECVT with 64 electrodes

Understanding particle flow characteristics within circulating fluidized bed (CFB) reactors is crucial for enhancing reaction efficiency. To study the flow characteristics of Geldart D particles with a mean diameter of 3.0 mm and a bulk density of 1640 kg/m3 in a CFB riser with a height of 1090 mm, a 64-electrode electrical capacitance volume tomography (ECVT) sensor with a height-to-diameter ratio (HDR) of 12 is arranged on the CFB riser with an inner diameter of 59 mm. A distributed ECVT architecture under the control of a timing controller is formed to synchronously acquire capacitance data of two 32-electrode ECVT data acquisition systems. So, the three-dimensional axial flow imaging of a CFB riser with a branch pipe is realized with a 14-plane ECVT sensor. The flow rules of slugging flow in the CFB riser under gas velocities of 3.5 m/s, 2.86 m/s, and 2.5 m/s are analyzed from the continuous ECVT images, especially the process of rupture, decomposition, and collapse of particle slugs. The flow parameter characteristics, such as the solid fraction in the riser, the slug rising tail velocity, the slug length, and the spectral characteristics, are investigated. The experimental results demonstrate that the proposed distributed ECVT can effectively realize the collaborative operation of multiple ECVT data acquisition systems and then splice sub-ECT images to achieve complex space imaging.

A Picofarad Capacitance Meter Based on Phase-Sensitive Demodulation for Tomography Application

Electrical capacitance volume tomography (ECVT) is an imaging technique based on the object’s capacitance value. To provide a representative image of the object under study, the ECVT system requires a method that can measure the capacitance value in the order of picofarads (pF). This level of resolution poses a difficulty for typical commercial capacitance measuring devices, hence raising the need for a specialized method with dedicated signal conditioning circuitry. The capacitance meter based on phase-sensitive demodulation (PSD) is made to solve the aforementioned issue and it is then compared with the characteristics of a capacitance meter-based commercial Arduino setup. The designed PSD-based capacitance measuring device has 97.894% accuracy, precision of 0.704 pF, sensitivity of 0.1197 V/pF, linearity with a coefficient of determination 0.9983, and stability of 0.028 pF/min. In comparison, the capacitance meter based on Arduino has 97.943% accuracy, precision of 0.027 pF, linearity with a coefficient of determination 0.9999, and stability of 0.04 pF/min. Testing is done on an 8-electrode ECVT sensor using dielectric materials of air and water. The nearest electrode pair on the condition of air as the dielectric medium has a capacitance value of 2.62218 pF for PSD-based measuring devices and 3.4027 pF for Arduino-based measuring devices, while the pair of electrodes on the condition of water as a dielectric medium has a capacitance value 9.8229 pF for measuring device based on PSD and 9.1069 pF for Arduino-based measuring devices. The opposite and farthest electrode pair on the condition of air as a dielectric medium has a capacitance value of 0 pF for PSD-based measuring devices and 0,0798pF for Arduino-based measuring devices, while the pair of electrodes on the condition of water as a dielectric medium has a capacitance value of 4.652 pF for PSD-based measuring devices and 0.1224 pF for Arduino-based measuring devices.

Imaging of unsaturated moisture flow inside cracked porous brick using electrical capacitance volume tomography

Concrete structures unavoidably suffer physical and chemical damage during service and hence easily crack. It is well-known that cracks in cement-based materials are preferential paths for the ingress of moisture and corrosive ions. Electrical capacitance volume tomography (ECVT) has previously been shown to be a powerful tool for imaging the spatial moisture distribution within cement-based materials. This paper investigated whether ECVT can be used for monitoring three-dimensional (3D) water penetration into porous materials containing different cracks. ECVT sensor with top electrodes and reconstruction algorithms were developed and evaluated respectively to improve the spatial resolution. The process of moisture ingress into bricks with different cracks was successfully visualized by ECVT, and the reconstructed results are in good agreement with the known properties of unsaturated water transport in porous materials. The ECVT reconstructions were also compared with moisture flow simulations, showing good agreement. Results suggest that ECVT is a viable tool for imaging 3D water penetration around cracks in porous materials, even for quantifying spatial water distribution.

Velocity Profiling of a Gas–Solid Fluidized Bed Using Electrical Capacitance Volume Tomography

In this work, a method of producing velocity profile maps from electrical capacitance volume tomography (ECVT) measurements by reconstructing displacement from measured changes in capacitance is developed and applied to fluidized bed systems. The mapping of the reconstruction leverages the gradient of the sensitivity distribution of the ECVT sensor to circumvent the need for image cross-correlation techniques. Experimental data of both bubbling and slugging fluidized beds are collected in a cold flow model. Adaptation of the technique is discussed in detail and velocity profiles are obtained for a range of gas flow rates. The produced velocity maps are compared against the established methods of cross-correlation and against empirical correlations from literature and are found to agree well in tracking slug and bubble velocity. The exception is when the tracked object is large relative to the ECVT sensor dimensions, a scenario that can be avoided through proper sensor design. The quantities of average velocity, momentum, and solids and gas volume fraction are derived from the image and velocity profiles. The results demonstrate and extend the power of ECVT as a measurement tool for the study and monitoring of gas-solid fluidized beds by providing a computationally cheaper alternative to 3-D cross-correlation for deriving velocity profiles.

Three-dimensional dynamic characterization of square-nosed slugging phenomena in a fluidized bed

Slugging represents one of the major regimes in fluidization, which occurs in small diameter beds with large bed height-to-diameter ratio or in large diameter beds with internals that resemble multiple small diameter fluidized beds. Slug types include round-nosed slug, wall slug and square-nosed slug. Studies of the slugs have been mainly focused on round-nosed or wall slugs known as half slug, typically occurring in Geldart group A particle fluidization. The square-nosed slug typically occurring for Geldart group D particles appears to be regarded as simple in its structure. The Electrical Capacitance Volume Tomography (ECVT) imaging of the square-nosed slugging phenomena conducted in this study reveals otherwise. That is the structure of the square-nosed slug is, in fact, complex, particularly with respect to its dynamic variation in fluidization. More broadly, this study examines experimentally the hydrodynamic characteristics of the square-nosed fluidization regime. Specifically, simultaneous measurements from multiple ECVT sensors provide non-invasive, continuous, 3-dimensional imaging of the entire flow region of the slugging bed and hence enabling the dynamic characterization of the evolution of the slugs. The analysis of the 3D images reconstructed for real-time gas–solid volume fraction profile of the slugging fluidized bed indicates that there are three different zones, namely, the bottom fluidization zone, the gas slug zone, and the solid slug zone, co-existing in the bed. The three zones present different hydrodynamic characteristics during the slug evolution. It is found that varying the gas velocity of the slugging bed mainly varies the maximum length of the gas slug zone, while it only has a minor effect on the lengths of the bottom fluidization zone and solid slug zone. It also has an insignificant effect on the solid volume fraction of the three zones.

Three-dimensional axial dispersion of gas-solid fluidized beds using 8-plane electrical capacitance volume tomography

Due to the complex flow characteristics and opaqueness of gas-solid fluidized beds, the axial behavior of circulating fluidized bed (CFB) risers is not entirely understood. A 32-electrode electrical capacitance volume tomography (ECVT) system with eight planes was developed to investigate the three-dimensional axial dispersion of gas-solid flow in a CFB riser. To maximize the imaging length in the axial direction, the 32-electrode ECVT sensor was designed with eight planes, with each plane containing four electrodes. The ratio of the axial imaging length to the sensor inner diameter was 8.3. We developed a 32-channel ECVT data acquisition system with an imaging speed of 120 frames per second to record the data of the ECVT sensor. Experimental results show that this ECVT system can effectively collect the flow details in the axial direction. The flow changed from slug flow to bubble flow when the fluidizing gas velocity Uf was adjusted from 2.34 m/s to 0.56 m/s. The distribution of the solid fraction, the velocity of the slug/bubble in the axial direction and the slug length were extracted from the 8-plane ECVT images to reveal the flow characteristics of the CFB riser.

Preliminary study on three-dimensional imaging of cryogenic two-phase flow based on electrical capacitance volume tomography

The potential application of electrical capacitance volume tomography (ECVT) to the liquid nitrogen-vaporous nitrogen two-phase flow measurement is evaluated by numerical experiment. The Landweber iteration is taken as the inversion algorithm which derives the reconstructed images. Eight types of ECVT sensor structures are tested and the accuracy of the reconstructed images is compared to evaluate the quality of the sensor structures. Especially, the effect of the axial guard electrodes is analyzed and discussed. The anti-noise ability of the optimal structure is also determined by calculating seven different phase distribution cases. The results demonstrate that the shifted plane and the axial guard electrode in ECVT sensor are helpful for image reconstruction quality. The layer number of ECVT sensor influences the reconstructed images a lot while the shape of the electrode has little effect on it. ECVT also shows a certain anti-noise ability under the noise level of 60 dB and 55 dB.

A Preliminary study of three-phase column flotation process monitoring using electrical capacitance volume tomography

A preliminary study of three-phase column flotation process using electrical capacitance volume tomography (ECVT) has been conducted. The purpose of this study is to investigate the possibility of ECVT method as a monitoring system by correlating the relative permittivity distribution (or three-dimensional image) with metallurgical performance (recovery of the process). Experiments were performed in a laboratory-scale flotation column with ECVT sensor embedded outside the pipe wall on the collection zone. The feed used was a synthetic ore consisting of sphalerite and silica with the purity of 99%. Process parameter used was air flow rate ranging from 2-4 l/m which each process was conducted for 10 minutes. The results showed that the ECVT method could observe the dynamic process of flotation, specifically in monitoring a feeding process and a separation process. They were indicated by increased and decreased relative permittivity distributions respectively. Relative permittivity signal and metallurgical performance have a good correlation and showed a positive correlation. These results show a prospect of ECVT method as the monitoring system in the flotation process, but further works need to be done for this monitoring system.

Slurry bubble column measurements using advanced electrical capacitance volume tomography sensors

A novel approach to studying dynamic three phase systems using Electrical Capacitance Volume Tomography (ECVT) is proposed and verified against previously published pressure gauge techniques and hydrodynamics patterns. In this three-phase study, hold up of water, glass beads, and air are measured simultaneously in a slurry bubble column reactor. Application of ECVT to investigate three phase systems holds several advantages over pressure gauges including the ability to deliver non-invasive real time direct measurements without making assumptions about the hydrodynamics. Results support the conclusion that ECVT can be used in place of pressure gauges to obtain accurate holdup measurements of three-phase flow systems in real time applications. The holdup of each phase inside of a three-phase slurry bubble column were measured using pressure sensors and an ECVT sensor. The results suggest that ECVT can be used in place of pressure sensors to obtain accurate holdup measurements of three-phase flows in real time. • Pressure and ECVT phase holdup measurements closely match. • ECVT reconstructed solid holdup images used to analyze bed expansion and contraction. • Solids and gas holdup measurements reflect hydrodynamic principles. • ECVT presents a valid replacement for pressure measurements in three-phase flows.

Experimental investigation of an internally circulating fluidized bed with 32-electrode electrical capacitance volume tomography

32-electrode electrical capacitance volume tomography (ECVT) was initially developed to investigate the inner flow characteristics of the internally circulating fluidized bed (ICFB) with baffle. The electrodes of the 32-electrode ECVT sensor were arranged based on their structure and dimension. The sensor characteristic was explored using the Finite Element Method. Additionally, a data acquisition system with 32-channel capacitance measuring units was also developed. The imaging speed of the 32-electrode ECVT system is 130 frames/s. Simultaneously, the experimental rig for the ICFB with baffle was constructed to investigate the characteristics of particle flow under different fluidizing gas velocities. The experimental results were then compared with the reported numerical simulations of ICFB.

Velocity Profiling of Multiphase Flows Using Capacitive Sensor Sensitivity Gradient

Velocity profiling of a flow involves the task of determining the velocity vector at every point in a given flow volume. A new method is proposed for velocity profiling of multiphase flows based on electrical capacitance volume tomography (ECVT) sensors. The proposed method utilizes a mapping between the change in measured capacitances and the displacement of flow that is effected by the spatial gradient of the sensitivity distribution. This novel mapping not only avoids the need for costly image cross correlations but also is fully compatible with existing ECVT sensor and image reconstruction algorithms. Simulation and measurement results are provided to demonstrate the proposed method.

Electrical Capacitance Volume Tomography (ECVT) for industrial and medical applications-An Overview

Tomography is a non-invasive, non-intrusive imaging technique allowing the visualization of phase dynamics in industrial and biological processes. This article reviews progress in Electrical Capacitance Volume Tomography (ECVT). ECVT is a direct 3D visualizing technique, unlike three-dimensional imaging, which is based on stacking 2D images to obtain an interpolated 3D image. ECVT has recently matured for real time, non-invasive 3-D monitoring of processes involving materials with strong contrast in dielectric permittivity. In this article, ECVT sensor design, optimization and performance of various sensors seen in literature are summarized. Qualitative Analysis of ECVT image reconstruction techniques has also been presented.

ELECTRICAL CAPACITANCE VOLUME TOMOGRAPHY: A COMPARISON BETWEEN 12- AND 24-CHANNELS SENSOR SYSTEMS

Spatial resolution represents a key performance aspect in electrical capacitance volume tomography (ECVT) systems. Factors affecting the resolution include the soft-field nature of ECVT, the number of capacitance channels used, the ill-conditioned nature of the imaging reconstruction problem, and the signal-to-noise ratio of the measurement apparatus. In this study, the effect of choosing different numbers of capacitance plates on the performance of ECVT is investigated experimentally. Specifically, two ECVT sensors with 12 and 24 capacitance channels but covering equal volumes of a cylinder are used to examine the resulting impact on the image resolution.

Electrical capacitance volume tomography for measurement soil water infiltration in vessel experiments

Electrical capacitance volume tomography (ECVT) is a recently-developed technique for real-time, non-invasive 3D monitoring of processes involving materials with strong contrasts in dielectric permittivity. This work is first application of the method to visualization of water flow in soil. We describe the principles behind the method, and then demonstrate its use with a simple laboratory infiltration experiment. 32 ECVT sensors were installed on the sides of an empty PVC column. Water was poured into the column at a constant rate, and ECVT data were collected every second. The column was then packed with dry sand and again supplied with water at a constant rate with data collected every second. Data were analyzed to give bulk average water contents, which proved consistent with the water supply rates. Data were also analyzed to give 3D images (216 voxels) allowing visualization of the water distribution during the experiments. Result of this work shows that water infiltration into the soil, wall flow, progress of the unstable wetting front and the final water distribution are clearly visible.

Bubbling fluidized bed characterization using Electrical Capacitance Volume Tomography (ECVT)

Abstract Understanding the fundamentals of gas–solid fluidized beds and, in general, multiphase flows has been a significant task since the conception of gas–solid fluidization and fluid particle systems. Various measurement techniques have been applied in an attempt to better understand the fundamentals of the complex gas–solid flow structures that form in fluidized beds. This information may potentially provide a better design, scale-up, and operation of these systems as well as lead to accurate performance predictions of multiphase flow systems. Electrical Capacitance Volume Tomography (ECVT) has now reached a point of development where these multiphase flow structures can be imaged accurately and reliably in three dimensions at good resolutions and sampling rates to provide significant insight into the internal gas–solid flow structures. A 10 cm ECVT sensor was used in order to investigate the bubble behavior of a 10 cm diameter bubbling fluidized bed (BFB) of 185 micron glass beads at various fluidization velocities. Three dimensional images of gas–solid flow structures as well as time average vertical and radial solid fraction profiles are presented in this paper, and average bubble diameter and bubble frequency are discussed and compared to various correlations available in the published literature.

Electrical capacitance volume tomography: design and applications.

This article reports recent advances and progress in the field of electrical capacitance volume tomography (ECVT). ECVT, developed from the two-dimensional electrical capacitance tomography (ECT), is a promising non-intrusive imaging technology that can provide real-time three-dimensional images of the sensing domain. Images are reconstructed from capacitance measurements acquired by electrodes placed on the outside boundary of the testing vessel. In this article, a review of progress on capacitance sensor design and applications to multi-phase flows is presented. The sensor shape, electrode configuration, and the number of electrodes that comprise three key elements of three-dimensional capacitance sensors are illustrated. The article also highlights applications of ECVT sensors on vessels of various sizes from 1 to 60 inches with complex geometries. Case studies are used to show the capability and validity of ECVT. The studies provide qualitative and quantitative real-time three-dimensional information of the measuring domain under study. Advantages of ECVT render it a favorable tool to be utilized for industrial applications and fundamental multi-phase flow research.

Electrical Capacitance Tomography − A Perspective

This article describes the recent progress in research and development on electrical capacitance tomography (ECT). Specifically, the article highlights several aspects of ECT including the electrical capacitance volume tomography (ECVT), 3D sensor design, 3D neural network multicriterion image reconstruction technique (3D-NN-MOIRT), multimodal imaging based on ECT and ECVT sensors, static-charge effects and the scheme of their elimination in the ECT image reconstruction, and multiphase flow imaging applications. The multimodal capability that enables permittivity and conductivity imaging to be simultaneously conducted is illustrated. The simulation and experimental results are presented to provide quantitative and/or qualitative assessment of the significance of various ECT techniques. The employment of ECVT in conjunction with using electrical capacitance based imaging sensors is shown to represent a favorable tool for industrial multiphase flow imaging.