Electrical resistance tomography for flow characterization of a gas-liquid-solid three-phase circulating fluidized bed

Electrical resistance tomography (ERT) as an imaging technique was employed in this study for flow characterization, including simultaneous measurements of phase holdups and velocity distribution of individual phases in a gas-liquid-solid circulating fluidized Bed (GLSCFB). Application of ERT in three-phase flow systems is completely new. ERT is a non-invasive technique based on conductivity of the continuous phase, which provides color-coded cross-sectional view of the phases with a frequency of up to 250 Hz. The local conductivity measured by 16 electrodes located at the periphery of the plane inside the ERT measurement section, was then further converted into local phase concentration distribution based on Maxwell's relation. By cross-correlation analysis between the data obtained from both upstream and downstream planes, each consisting of eight electrodes, the phase propagation velocity was determined. Water was used as the continuous and conductive phase, while glass beads and air were non-conductive solid and gas phases, respectively. Qualitative and quantitative radial profiles of the phase holdup and propagation velocities were obtained. Phase holdup was also measured by pressure fluctuation, using online non-invasive pressure transducers and the results were in close agreement with the ERT results.     

Electrical Resistance Tomography (ERT) applications to Chemical Engineering

Electrical Resistance Tomography (ERT) has the capability of offering time-evolving multidimensional comprehensive process knowledge, enrichment of fundamental process understanding and enhancement of the design and operation of process equipment by measuring the conductivity distribution within a process-plant of interest. This paper reviews the wide variety of previous work on ERT applications to Chemical Engineering. The applications are categorized based on the unit operations ERT has been applied to, the media under investigation, the purpose of ERT measurements and also other technologies used in conjunction with ERT. The aim of this taxonomy is to provide the reader with a general understanding of the current situation of ERT related research and proven applications in the Chemical Engineering field and to facilitate the recognition of research gaps for future investigation. Based on this detailed taxonomy and review the potential application of ERT to the milk powder processing industry was identified. Some results of the application of ERT to milk mixing/holding tanks and milk flow pipelines for the purpose of concentration and composition measurements, detection of abnormalities and faults, and multidimensional flow and velocity profile measurements have also been presented as a case study of using this taxonomy.     

Making use of process tomography data for multivariate statistical process control

A novel strategy for making effective use of on‐line process tomography measurements for process monitoring is described. The electrical resistance tomography (ERT) sensing system equipped with sixteen electrodes provides 104 conductivity measurements every 25 ms. The data has traditionally been used for construction of images for display purpose. In this study, ERT data was used for multivariate statistical process control. Data at predefined normal operational conditions was processed using principal component analysis. The compressed data was used to derive two statistics, T² and squared prediction error (SPE). T² and SPE charts predict the probability that the process being monitored has undergone statistically significant changes from previous state or the so‐called normal operational state, in terms of mixing quality. The methodology is illustrated by reference to a case study of a sunflower oil/water emulsion process. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Development of an Electrical Resistance Tomography Reactor for Pharmaceutical Processes

A review of tomography systems suitable for industrial implementation and design considerations for tomographic sensors has allowed the design of an ERT sensor compatible with stringent process requirements. In conjunction with a data acquisition system, ITS P2000, this sensor was applied to processes considered typical of Active Pharmaceutical Ingredients (API) chemical development. Experimental results are described where variations in conductivity measurements were monitored in a stirred tank. The data were compared with spectroscopic on‐line monitoring and kinetic information. The results obtained demonstrate that this approach shows promise for on‐line control of mixing process performance and efficiency evaluation and optimisation of reactor geometries.     

Application of electrical resistance tomography on liquid-solid two-phase flow characterization in an LSCFB riser

The application of liquid-solid circulating fluidized beds (LSCFB) is steadily increasing in the chemical, biochemical and other industries. Electrical resistance tomography (ERT) as an imaging technique was employed for the study of flow parameters such as phase holdup, velocity distribution of individual phases in LSCFB. ERT is a non-invasive technique based on conductivity measurement of the continuous phase, which also provides color-coded cross-sectional view of phases with a frequency of up to 250 images per second. The local conductivity measured by a number of electrodes located at the periphery of the plane was then further converted into a local phase concentration distribution based on Maxwell's relation. Local solids holdup also measured by using optical fibre probe to compare and verify the result obtained by ERT. By cross-correlation between the data obtained from a pair of planes of ERT, one upstream and one downstream, the phase propagation velocity was determined. Water was used as the continuous and conductive phase and glass beads and lava rocks (LR) of 500 μm sizes were used as the solid and non-conductive phase in this investigation. Radial non-uniformity of phase holdups was observed at different superficial liquid velocities. Solids holdup was higher in regions close to the wall and low in the central area. Such non-uniformity in phase holdup decreased with increasing liquid velocity. Both solids holdup and radial non-uniformity increased with superficial solids velocity. The solids propagation velocity increased in the central region under different superficial liquid velocities. Good agreement was observed between the data obtained from the two methods.     

Characterisation of the mixing of non‐newtonian fluids with a scaba 6SRGT impeller through ert and CFD

An attempt has been made to study the mixing of yield‐pseudoplastic fluids with a Scaba 6SRGT impeller using electrical resistance tomography (ERT) and computational fluid dynamics (CFD). The ERT system with four sensor planes, each containing 16 equispaced stainless steel electrodes, was used to measure the mixing time. The multiple reference frames (MRF) technique and the modified Herschel–Bulkley model were applied to simulate the impeller rotation and the rheological behaviour of the non‐Newtonian fluids, respectively. To validate the model, the CFD results for the power consumption were compared to the experimental data. The validated model was then employed to obtain further information regarding the averaged impeller shear rate, impeller circulation, and pumping capacities. The CFD and ERT data were utilised to investigate the effect of the impeller power, fluid rheology, and impeller size on the mixing time. The mixing time results obtained in this study were in good agreement with those reported in the literature. © 2011 Canadian Society for Chemical Engineering     

Electrical resistance tomography (ERT) for flow and velocity profile measurement of a single phase liquid in a horizontal pipe

Electrical resistance tomography (ERT) is a novel, simple, and robust method of process imaging which uses non-invasive sensors located on the periphery of vessels to reconstruct a cross-sectional image of the vessel interior. This method of imaging when conducted on two adjacent planes on a pipe provides the ability to extract flow information. Previous studies have investigated this application on multi-phase flows in which the secondary phase provided the required pulse conductivity variation. In these studies the velocity profile and flow regime were identified using the common cross-correlation technique.     

Characterization of slurry flow regime transitions by ERT

Slurry flows in a pipe have been visualized using electrical resistance tomography (ERT). Complementary to image reconstruction technique, a strategy based on the direct interpretation of the raw ERT measurements has been developed to analyze slurry flow regimes in a horizontal pipe. Experiments have been conducted using a lab-scale pipe loop equipped with a commercial ERT device. The images of slurry concentration have been reconstructed using an iterative Landweber method and compared to a direct linear back-projection (LBP) method available in the ERT software. The slurry concentration has been estimated and the homogeneity of the concentration distribution has been assessed directly from resistance measurements and a simple resistance model. It is shown that this procedure, combining the image reconstruction and the direct interpretation of ERT measurements, allows analyzing the slurry flow regimes and transitions for slurry concentrations up to 20% v/v and velocities up to 2.2 m/s.     

Tomographic imaging during reactive precipitation in a stirred vessel: Mixing with chemical reaction

Electrical resistance tomography (ERT) allows the user to non-invasively ‘see inside their process’ through the manipulation and measurement of electrical properties enabling a powerful real-time visualisation of the time evolving three-dimensional conductivity distributions within the process unit. A 4-plane 16-sensor ERT array retrofitted to a 7.5 l stirred vessel has been used to rigorously interrogate the single feed semi-batch precipitation of barium sulphate, providing over 1000 spatially varying data points per ‘captured’ frame. A variety of reactant concentrations and agitation intensities were investigated. The results obtained reflect both the hydrodynamics and complex reaction kinetics involved with reactions and detail a number of very distinct regions during the experimental runs. This is achieved through the direct visualisation of the induced feed plume, quantification of the homogeneity (‘mixedness’) within the vessel, time evolving conductivity trends and a further analysis into the rates of conductivity changes as the reaction proceeds. For some experimental runs the predicted conductivity trends for a perfectly mixed state have been calculated using a conductivity-concentration correlation. ERT offers many spatially varying data points as opposed to point wise measurements which offers a significant improvement for the validation of mathematical models which attempt to deal with reactive crystallisation. As well as data collection, specifically for model validation, ERT may offer the means to control the spatio-temporal distributions of reactants and phases within the reactor to aid the suppression of unwanted by-products for industrial processes whilst offering a means to monitor the process unit to ensure the required mixing intensity is always achieved. Also included is an analysis of the mean volume diameter of the precipitate for each experimental run with scanning electron microscope (SEM) images.     

基于ERT技术的硫酸钡颗粒形成过程研究

采用电阻层析成像技术（ERT）实时监测反应器内横截面电导率变化,进而考查络合法形成球形硫酸钡颗粒的过程中溶液电导率变化趋势。在拟均相条件下,根据ERT实时监测、采集、分析硫酸钡颗粒生成过程中电导率变化情况,得出电导率变化曲线,并采用扫描电子显微镜方法观察随着反应时间变化硫酸钡颗粒的形态变化情况。实验结果表明,使用ERT监测电导率变化可以得出不同浓度条件下电导率变化趋势及其浓度条件下的最适宜反应时间,并验证了采用电阻层析技术（ERT）对研究硫酸钡颗粒的形成具有较高的灵敏度,可用于研究硫酸钡颗粒的形成最适宜时间;用扫描电子显微镜观察络合法合成硫酸钡最开始形成一种梭型颗粒,随着钡离子的缓慢释放,硫酸钡颗粒不断生长,最终得到粒度均匀、分散性良好的球形硫酸钡颗粒。     

Electrical conductivity method to assess static stability of self-consolidating concrete

The objective of this study is to evaluate the applicability of the electrical conductivity method to assess the stability of self-consolidating concrete (SCC) at early age. The method consists in inserting four electrode pairs at different depths of concrete to monitor local change in ionic concentrations with time. Such variations can reflect migration of bleed water along concrete column during the plastic stage. The experimental set-up consisted of a rectangular column measuring 1005 mm in height and 250 × 250 mm in cross section. The variations in ionic concentrations were exploited to derive stability indices with regards to bleeding and homogeneity of concrete. Derived stability indices included bleeding coefficient, segregation coefficient, and homogeneity index.Various SCC mixtures made with a fixed water-to-cementitious materials ratio (w/cm) of 0.42, different aggregate gradations, and slump-flow values of 650 ± 10 and 700 ± 10 mm were evaluated. Analysis of changes in ionic concentrations along column samples with time provided adequate evaluation of stability of SCC. For example, the increase in the concentration of viscosity-modifying admixture from 1% to 2% was shown to decrease the homogeneity index from 0.36 to 0.27, reflecting better stability. Validation procedure was carried out by correlating stability indices derived from electrical conductivity measurements to physical variations of coarse aggregate concentrations determined on plastic concrete sampled from the tested column elements at the end of electrical conductivity monitoring period. Good correlations between stability indices and aggregate concentrations are established.     

Techniques for visualization of cavern boundaries in opaque industrial mixing systems

In the agitation of complex fluids, the avoidance of caverns is essential for successful blending. Electrical resistance tomography (ERT) and positron emission projection imaging, which can both image within opaque fluids, have been assessed for visualization of cavern boundaries. A vessel of diameter, T = 154 mm, equipped with a single 57 mm diameter six bladed 45° down pumping pitched blade disc turbine formed the test system. The fluid used was aqueous solution of carbopol 940. Both techniques were used to detect and image caverns at Re from 20–86.6 and compared with optical images. Reasonable agreement on the maximum cavern heights and widths were obtained, with the taller and narrower caverns obtained via 3D ERT measurements being attributed to artifacts of the method and interactions between the polymer and tracer. Caverns were also detectable using a robust linear ERT array, which has potential for use within industrial systems. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Damage detection in 2.5D C/SiC composites using electrical resistance tomography

In this work, an innovative method for the detection of damage in fiber-reinforced ceramic matrix composites (CMCs) is introduced. For electrically conductive CMCs, the conductivity distribution is coupled with the internal damage, which enables the realization of structural health monitoring (SHM). In this research, we verify the feasibility of using electrical resistance tomography (ERT) for damage detection in CMCs. The nature of conductivity anisotropy was considered. Local damage was introduced and was evaluated through ERT. Different injection patterns and values of the regulation parameter were compared to obtain optimal spatial resistivity mapping imaged via ERT. The effect of typical damage states on the resistivity was quantified to determine the theoretical resolution of ERT for damage detection in the 2.5D C/SiC composite. The present study serves as a further step into introducing ERT as a promising SHM method which can be implemented to CMCs for in situ and non-destructive inspection.     

Impedance spectroscopy study of hardened Portland cement paste

In this paper, the differential impedance analysis (DIA) has been applied to the study of the dielectric properties of hardened Portland cement paste. Two time constants are found in the impedance spectra obtained in the frequency region form 100 kHz to 15 MHz. One time constant has been attributed to the solid matrix and the other one to the liquid phase filling the pores. The effect of the cement paste-electrodes interface has been quantified using two different experimental set-ups. Measurements using direct contact between electrodes and cement paste have been compared with measurements using an air gap technique in which the specimen “floats” between the electrodes. The two referred time constants have been found in both types of measurements. The influence of drying on the dielectric parameters is also studied.     

用于多相流测量的并行模式电阻层析成像系统设计(英文)

ERT(electrical resistance tomography) is effective method for visualization of multiphase flows,offering some advantages of rapid response and low cost,so as to explore the transient hydrodynamics.Aiming at this target,a fully programmable and reconfigurable FPGA(field programmable gate array)-based Compact PCI(peripheral component interconnect) bus linked sixteen-channel ERT system has been presented.The data acquisition system is carefully designed with function modules of signal generator module;Compact PCI transmission module and data processing module(including data sampling,filtering and demodulating).The processing module incorporates a powerful FPGA with Compact PCI bus for communication,and the measurement process management is conducted in FPGA.Image reconstruction algorithms with different speed and accuracy are also coded for this system.The system has been demonstrated in real time(1400 frames per second for 50 kHz excitation) with signal-noise-ratio above 62 dB and repeatability error below 0.7%.Static experiments have been conducted and the images manifested good resolution relative to the actual object distribution.The parallel ERT system has provided alternative experimental platform for the multiphase flow measurements by the dynamic experiments in terms of concentration and velocity.     

Assessing Blending of Non‐Newtonian Fluids in Static Mixers by Planar Laser‐Induced Fluorescence and Electrical Resistance Tomography

Planar laser‐induced fluorescence (PLIF) and electrical resistance tomography (ERT) were applied simultaneously to monitor the mixing performance of a KM static mixer for the blending of non‐Newtonian fluids of dissimilar rheologies in the laminar regime. The areal distribution method was used to obtain quantitative information from the ERT tomograms and the PLIF images. Comparison of the ERT and PLIF results demonstrates the ability of ERT to detect the mixing performance in cases of poor mixing within the resolution of the measurement, though the accuracy decreases as the condition of perfect mixing is approached. Thus, ERT has the potential to detect poor mixing within the confines of its resolution limit and the required conductivity contrast, providing potential rapid at‐line measurement for industrial practitioners.     

Current distribution measurements in a PEFC with net flow geometry

A measurement system for current distribution mapping for a PEFC has been developed. The segmented anode is constructed so as to have high thermal conductivity in order to prevent the formation of large temperature gradients between the electrodes. The construction is therefore feasible for use at high current densities. Both segmented and unsegmented gas diffusion layers are used. The effect of inlet humidification and gas composition at the cathode side is studied. In addition, two different flow geometries are studied. The results show that the measurement system is able to distinguish between current distribution originating from differences in proton conductivity, species concentration and gas diffusion layer properties.     

Characterising aggregate surface geometry in thin-sections of mortar and concrete

Measurement of microstructural gradients at the aggregate/cement paste interfacial transition zone (ITZ) in hardened mortar and concrete is commonly performed via quantitative image analysis of multiple micrographs of specimen surfaces, using a scanning electron microscope. However, due to the random orientation of interfaces sectioned by the specimen surface, measurements of the microstructural gradients at the interface have an unknown angular component, and thus have an unknown error. We present a method for the identification of interfaces that are perpendicular to the specimen surface, and therefore, are more suitable for accurate ITZ analysis. This method employs simple optical and electron imaging techniques on petrographic thin-sections. Use of 3D laser scanning confocal microscopy helped to validate the method. Quantitative 2D image analysis of backscattered electron micrographs, captured over three angular classes of interface gives an indication of this error in the determination of interfacial porosity and anhydrous cement content.     

Applicability of electrical resistance tomography to the analysis of fluid distribution in haemodialysis modules

This work aims to explore the applicability of electrical resistance tomography (ERT) in the analysis of fluid distribution in haemodialysis modules, which is not straightforward due to the complex geometry of the hollow fibre bundles and the small sizes of the modules. On the other hand, ERT is potentially a suitable and convenient technique for investigation in this field due to its cost-effectiveness and capacity to perform measurements in opaque systems. After a preliminary estimation of the fibre bundle local distribution, the assessment of the technique is performed by observing the time evolution of the measured conductivity maps during the module filling and emptying operations with water and air, which are alternatively fed inside or outside the fibre bundle. Reliable conductivity maps are obtained by placing the module vertically or horizontally. Additional experimental data collected by feeding liquid mixtures of different sodium chloride concentrations show that the technique is suitable for detecting concentration variations, due to the mass transfer through the fibres, and flow maldistribution, due to the specific geometry of the module. From the preliminary results collected in this work, the technique appears to be adequate for the collection of data that can support the optimization of the module geometry and computational model validation.     

Simulation of residual stress in thick thermal barrier coating (TTBC) during thermal shock: A response surface-finite element modeling

The current study demonstrates a well-designed response surface methodology (RSM), based on the generated dataset of finite element method (FEM) to establish an integrated model for simulation of residual stress distribution in a thick thermal barrier coating (TTBC). In this study, typical TTBCs were applied on Hastelloy X Nickel-based superalloy using air plasma spray technique followed by thermal cycling. The recorded stress data of Raman spectroscopy was employed to verify the proposed FEM model. A relatively good agreement was obtained between predicted residual stresses and measured ones. Verified FEM model was used to carry out the parametric studies to evaluate the effects of such various parameters as interface amplitude, wavelength, thermally grown oxide thickness and preheating temperature on the stress distribution in the TTBC during the thermal cycling. The computed data were subsequently used for the development of RSM model. In conclusion, experimentally verified numerical data was used to construct a statistical model based on RSM and successfully used to predict the residual stress distribution field in TTBC during thermal cycling. The obtained results of hybrid FEM- RSM model were in acceptable conformity with Raman spectroscopy measurements.