Electric Capacitance Tomography Research Articles

Evaluation of Landweber Coupled Least Square Support Vector Regression Algorithm for Electrical Capacitance Tomography for LN2–VN2 Flow

The electric capacitance tomography (ECT) technique has been widely used in phase distribution reconstruction, while the practical application raised nonideal noise and other errors for cryogenic conditions, requiring a more accurate algorithm. This paper develops a new image reconstruction algorithm for ECT by coupling the traditional Landweber algorithm with the least square support vector regression (LSSVR) for cryogenic fluids. The performance of the algorithm is quantitatively evaluated by comparing the inversion images with the experimental results for both the room temperature working medium with the dielectric constant ratio close to cryogenic fluid and the cryogenic fluid of liquid nitrogen/nitrogen vapor (LN2-VN2). The inversion images based on the conventional LBP and Landweber algorithms are also presented for comparison. The benefits and drawbacks of the developed algorithms are revealed and discussed, according to the results. It is demonstrated that the correlated coefficients of the images based on the developed algorithm reach more than 0.88 and a maximum of 0.975. In addition, the minimum void fraction error of the algorithm is reduced to 0.534%, which indicates the significant optimization of the LSSVR coupled method over the Landweber algorithm.

Multiphase jet penetration in gas-solid systems

Thermochemical conversion of biomass in fixed/fluidized bed reactors requires efficient feedstock penetration and dispersion through reliable feed injection systems. Pneumatic biomass injection produces a gas-solid jet in the reactor that requires proper momentum to disperse the feedstock. Assessing multiphase jet penetration in fluidized beds is challenging because of system's complexity, opaqueness and lack of a universal measurement technique adapted for tracking the associated phenomena. In this work, three measurement techniques (fluorescent particle tracking, pitot tubes and Electric Capacitance Tomography (ECVT)) were employed and compared to assess the penetration of air-biomass jets into fixed/fluidized beds. Results from all techniques indicated that the jet penetration increased with solids mass flux, and jets with similar momentum provide greater penetration in fluidized beds compared to fixed beds. Tridimensional jet propagation and biomass concentration across the jet length were obtained for different operating conditions providing a useful database for CFD and other mechanistic models validation.

A simple method for detecting very small changes in capacitance or inductance

A simple method for detecting very small changes in capacitance or inductance is presented. In the circuit used in the proposed method, which employs LC resonance, the phase of the output signal sharply and monotonically changes by about 180° around the resonance frequency. When the capacitance or inductance changes slightly, the resonance frequency shifts accordingly. This change can be sensitively detected as a phase shift of the output signal by applying a fixed frequency signal to the circuit near the resonance frequency. The circuit used for detection is entirely composed of general-purpose electronic components and does not use special function devices. This method can be applied in various practical contexts, for example, object detection, proximity sensing, monitoring material properties, and electric capacitance tomography.

Issue: Selected paper of OIPE 2016 on modeling and optimal design of electromagnetic and electronic devices

Issue: Selected paper of OIPE 2016 on modeling and optimal design of electromagnetic and electronic devices

Flame Detection on Swirl Burner Using ECT With Dynamic Reconstruction Algorithm Based on the Split Bregman Iteration

To achieve increased combustion efficiency and reduced pollutant generation, methods to describe the spatial distribution of combustion parameters, such as combustion intensity and temperature are desired. Electric capacitance tomography (ECT) is by nature sensitive to the electrical properties of a flame, facilitating combustion intensity imaging. In this paper, a novel image reconstruction algorithm is developed. It is based on an enhanced regularization methodology and adequate fusion of prior knowledge in the optimization of the objective functional through which a higher spatial resolution and lower errors of the reconstructed images are realized. Simulation results show very good agreement of the reconstructed images with typical phantoms. Also, a series of experiments are carried out for a range of flow rates of fuel and air. Data are collected by the ECT sensor and hardware, and the corresponding images are reconstructed by the new algorithm. The experiments demonstrate the advantages of the new method and ECT images correspond well with the variation of the combustion intensity. Further analysis agrees well with the established principle of combustion.

Electric capacitance tomography for nondestructive testing of standing trees

AbstractIn this paper, an innovative Artificial Neural Network (ANN)‐based approach to solve the bi‐dimensional Electric Capacitance Tomography inverse problem is proposed in order to assess the health state of standing trees. Using a set of examples, an ANN is trained to solve the direct problem, ie, to associate the properties of the tree trunk affected by defects to a set of capacitance values. Then, the trained ANN is inverted in order to obtain the defect position and dimensions on the basis of measured capacitance values. The potentiality of the method is presented making reference to several target examples.

Tomographic data fusion with CFD simulations associated with a planar sensor

Tomographic techniques have great abilities to interrogate the combustion processes, especially when it is combined with the physical models of the combustion itself. In this study, a data fusion algorithm is developed to investigate the flame distribution of a swirl-induced environmental (EV) burner, a new type of burner for low NOx combustion. An electric capacitance tomography (ECT) system is used to acquire 3D flame images and computational fluid dynamics (CFD) is applied to calculate an initial distribution of the temperature profile for the EV burner. Experiments were also carried out to visualize flames at a series of locations above the burner. While the ECT images essentially agree with the CFD temperature distribution, discrepancies exist at a certain height. When data fusion is applied, the discrepancy is visibly reduced and the ECT images are improved. The methods used in this study can lead to a new route where combustion visualization can be much improved and applied to clean energy conversion and new burner development.

Sensing flame structure by process tomography.

Non-intrusive visualization of the structure of flames can offer us many advantages in studying the reaction mechanisms of combustion and observing special distributions of the parameters required for the development of equipment such as jet engines and gas turbines. Process tomography is a relatively new technique for such a task, but is useful owing to its fast speed and capability of detecting signals related to ionizations caused by chemical reactions and thermal effects. Electric capacitance tomography (ECT) is one of the process tomographic techniques. ECT usually comprises a sensor array of electrodes that detect permittivity variations in the measuring zone, a data-logging device and a computer that controls data acquisition and carries out image reconstruction. There have been studies on ECT imaging of flames; however, ECT has not been exploited sufficiently to reveal the inner structure of the flames. In this study, a sensor with planar electrodes is created, and the associated three-dimensional sensitivity map is generated by the finite-element method to detect flame structure. A series of experiments are carried out covering a range of feed rates of fuel and air. Data are collected by the ECT sensor and hardware. The results of the ECT reconstruction show good agreement with actual features, and the structure of the flame is found. This opens up a new route for the study of flames. This article is part of the themed issue 'Supersensing through industrial process tomography'.

Experimental study on the condensation of a thermosyphon by electrical capacitance tomography

The study on the condensation and the two-phase flow pattern in the condensation section is important to understand the operating mechanisms in a thermosyphon. In this paper, a new electric capacitance tomography (ECT) sensor was designed for the visualization measurement in a liquid by removing the shielding case and sealing with insulating hydrophobic material. It was successfully used to measure the condensation process in a thermosyphon under different operating temperatures. The thermosyphon was made of silica glass, and alcohol was used as a working fluid. The alcohol vapor was cooled to condense through the heat convection with the cooling water. The operating temperature was controlled by a heater with different power outputs. The experimental results show that the alcohol vapor condensed in stripes and unevenly on the wall surface at a low operating temperature. The liquid bridge will be formed periodically at the operating temperature of 90°C, and the time interval between two liquid bridges will be shorter with the increase of the operating temperature. At 117°C or even higher operating temperatures, the complete liquid bridge cannot be formed sometimes due to the difference of the growth rate of the surface wave around the circumference.

Decoupling the joint effect of moisture and mass in dense phase pneumatic conveying

Electric capacitance tomography (ECT) is advantageous for online imaging of pneumatic conveying of solids. From the ECT images, the spatial distribution of the mass of the material can be displayed at a very fast speed. However, as the mass distribution and the permittivity of the solids simultaneously affect the values of the measured capacitance arrays, they cause a coupled effect on the ECT images. In situations where the permittivity of the solids is influenced by the moisture, and this influence cannot be separated from the influence of the mass, or cannot be accounted for by an appropriate means, the measurement will be erroneous, as ECT images are usually interpreted as the distribution of the mass alone. This study aims to tackle the problem by an attempt to decouple the combined influence of the mass and the permittivity. A sensor of narrow electrodes is designed for the purpose of detecting only the variations in the permittivity. Simulation and experimental results both demonstrated that the influence of the permittivity and the mass of the solids can be decoupled under certain conditions, which provide a mechanism to correct the possible errors due to the unknown variation of the solids permittivity, or moisture.

Distributed parameter control of a batch fluidised bed dryer

In this paper, a distributed parameter approach is used to model and control a batch fluidised bed dryer. Electric capacitance tomography (ECT) is used as a sensor to measure and control the distributed permittivity in the bed. First, a lumped model is developed to describe the heat and mass transfer between solid, gas and bubble phases in the bed. Then, based on this model, a distributed parameter model is developed to predict the permittivity distribution. Experimental validation confirms the accuracy of the model. Finally, a distributed parameter controller is designed and implemented to regulate the permittivity distribution.

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

In gas-solid fluidized beds, the distribution of the particles typically varies both in time and space. Since the gas-solids distribution and its variation have a strong influence on the performance of a fluidized bed for a given process, it is very important to accurately measure the gas-solids or voidage distribution. This paper reviews techniques for measuring the voidage distribution in gas-solid fluidized beds, with a focus on the developments during the last ten years. We will treat subsequently direct visualisation, tomography, optical probes, capacitance probes, and pressure measurements.Dense gas-solids flows are typically opaque to visible light. This makes optical techniques only of limited use in dense gas-solids flow. However, direct visualization can be useful for very dilute systems, pseudo 2-D beds, and the outer layer of dense, 3-D systems. Tomography is frequently used to obtain the voidage distribution in a horizontal cross-section of the bed. Electric capacitance tomography is fast, but its spatial resolution is limited and image reconstruction is still troublesome. Although some steps forward have been made, research is continuing at this point. For nuclear (X-ray and gamma-ray) tomography, the image reconstruction is much easier and the spatial resolution better, but its temporal resolution is typically much lower. Therefore, research efforts for nuclear tomography are mainly aimed at increasing the measurement frequency. Optical probes determine the voidage as a function of time in a small measurement volume, either by the degree of reflection or by the degree of transmission of a light bundle. Capacitance probes determine the voidage as a function of time in a small measurement volume by measuring the dielectric permittivity of the gas-solids suspension in the measurement volume. Both optical and capacitance probe techniques are reasonably well-developed; the current research effort spent at improving them seems limited, especially for capacitance probes. Time-averaged pressure measurements are commonly used to determine the average bed density and bed height. By sampling the local pressure at a sufficiently high frequency (typically in the order of 200 Hz), much more information can be obtained about the fluidized bed hydrodynamics. However, obtaining quantitative voidage data from pressure fluctuations measurement remains a difficult task; in-bed pressure fluctuation (and acoustic) measurements are mostly used to determine changes in the voidage dynamics and distribution.

Heterogeneous structure in gas–solid riser flows

AbstractRecent measurements by electric capacitance tomography reveal that, under certain operating conditions, the solids concentration distribution in the dense and acceleration regimes of gas–solid riser flows exhibits a strong heterogeneous structure, with the solids concentration near the centerline much higher than that in the annular surrounding flows (except in the wall region) within the same cross‐section. This core–annulus–wall heterogeneous structure, significantly different from the commonly known “core–annulus (wall)” two‐zone structure in riser flows, becomes unstable with the increase in solids loading, which eventually leads to the occurrence of choking. In this study, we propose a mechanistic model to investigate the formation and distribution of these interesting heterogeneous structures in riser flows. The intrinsic mechanisms include (1) counterflow between back mixing solids and upward moving solids from entrance, (2) the radial migration of solid flow from the wall toward the centerline of riser, and (3) the nonuniform acceleration of solids across the cross‐section in the dense and acceleration regimes. The model, assuming one‐dimensional two‐phase flow in each zone along the riser, consists of a set of coupled ordinary‐differential equations developed from the conservation laws of mass, momentum, and energy of both gas and solids phases. The solving algorithm is based on the Runge‐Kutta method. Our model calculations show that the commonly known “core–annulus (wall)” flow structure occurs at low solids loadings and/or high gas velocities, whereas the core–annulus–wall flow structure is formed at moderate solids loading and/or at low gas velocities. With a high solids loading at low gas velocity, severe backflow results in a solid concentration peak formed in the core, which not only causes the flow instability but also possibly triggers the choking. Model simulations are validated by direct comparisons against measurements in solids concentrations as well as in the pressure drop along the riser, which shows a fairly good agreement. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Transient processes and noise in a tomography system: an analytical case study

This paper presents an analysis and optimization of an ac-based electric capacitance tomography system. The existing system can capture image data up to 250 frames/s. However, even higher acquisition rates, say 2000 frames/s are desirable for some applications. To optimize the system design, a transient process analysis is performed for every analog stage to determine the settling time and an approach is suggested to minimize it. Noise analysis is also performed to ensure that the signal-to-noise ratio of the system does not degrade. In both cases, results are validated by simulation using PSpice and/or by experiment, showing that the settling time of the overall system could be reduced from 4.4 to 1 ms, offering a faster data acquisition rate of 1000 frames/s.

Evaporative liquid jets in gas–liquid–solid flow system

Some aspects of the fundamental characteristics of evaporative liquid jets in gas–liquid–solid flows are studied and some pertinent literature is reviewed. Specifically, two conditions for the solids concentration in the flow are considered, including the dilute phase condition as in pneumatic convey and the dense phase condition as in bubbling or turbulent fluidized beds. Comparisons of the fundamental behavior are made of the gas–solid flow with dispersed non-evaporative as well as with evaporative liquids. For dilute phase conditions, experiments and analyses are conducted to examine the individual phase motion and boundaries of the evaporative region and the jet. Effects of the solids loading and heat capacity, system temperature, gas flow velocity and liquid injection angle on the jet behavior in gas and gas–solid flows are discussed. For dense phase conditions, experiments are conducted to examine the minimum fluidization velocity and solids distribution across the bed under various gases and liquid flow velocities. The electric capacitance tomography is developed for the first time for three-phase real time imaging of the dense gas–solid flow with evaporative liquid jets. The images reflect significantly varied bubbling phenomenon compared to those in gas–solid fluidized beds without evaporative liquid jets.

Lectric Capacitance Volumetric Tomography ECVT for Fuel Gauging Under Zero Gravity

To better allow for measurement of liquids, such as propellant, in microgravity, the University of Wisconsin – Madison ZeroG Team conducted an experiment using electric capacitance and volumetric tomography. This procedure allowed for 3D computer imaging of the internal contents of a reservoir to determine the volume of substance inside. For this experiment, polypropylene spheres were used to eliminate the hazards of having fuel inside the cabin of the aircraft. Full analysis of the flight procedures can be seen below.Â