The Effect of Sparger Geometry on Gas Bubble Flow Behaviors Using Electrical Resistance Tomography

By electrical resistance tomography (ERT) the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution is re-vealed by applying a sensitivity conjugated gradients reconstruction method (SCG). Experimental results show that over-all hold-up obtained by ERT is generally in good agreement with those measured with the pressure transducer and the ERT system produces informative evidence that the radial profiles of hold-up is very similar to the sparger design in the lower section of bubble column. Meanwhile, the rise velocity of bubble swarm and the Sauter mean bubble size are evaluated using ERT based on dynamic gas disengagement theory. The experimental results are in good agreement with correlations and conventional estimation obtained using pressure transmitter methods.

An adaptive electrical resistance tomography sensor with flow pattern recognition capability

The all traditional electrical resistance tomography (ERT) sensors have a static structure, which cannot satisfy the intelligent requirements for adaptive optimization to ERT sensors that is subject to flow pattern changes during the real-time detection of two-phase flow. In view of this problem, an adaptive ERT sensor with a dynamic structure is proposed. The electrodes of the ERT sensor are arranged in an array structure, the flow pattern recognition technique is introduced into the ERT sensor design and accordingly an ERT flow pattern recognition method based on signal sparsity is proposed. This method uses the sparse representation of the signal to express the sampling voltage of the ERT system as a sparse combination and find its sparse solution to achieve the classification of different flow patterns. With the introduction of flow identification information, the sensor has an intelligent function of adaptively and dynamically adapting the sensor structure according to the real-time flow pattern change. The experimental results show that the sensor can automatically identify four typical flow patterns: core flow, bubble flow, laminar flow and circulation flow with recognition rates of 91%, 93%, 90% and 88% respectively. For different flow patterns, the dynamically optimized sensor can significantly improve the quality of ERT image reconstruction.

Design of Parallel Electrical Resistance Tomography System for Measuring Multiphase Flow

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.

Detecting the Resistivity Distribution of Carbon Fiber Reinforced Concrete by Electrical Resistance Tomography Method

According to the principle of electrical resistance tomography （ ERT）, the resistivity distribution of the carbon fiber reinforced concrete （CFRC） in the sensing field can be measured by injecting exciting current and measuring the voltage on the sensor electrode arrays installed on the surface of the object. Therefore, measurement of the resistivity distribution of CFRC is divided into first measuring the boundary conditions and then inversely computing the resistivity distribution. To reach this goal, an ERT system was constructed, which is composed of a sensor array unit, a data acquisition unit and an image reconstruction unit. Simulations of static ERT was performed on set-ups with many objects spread in a homogeneous background, and a simulation of dynamic ERT was also done on a rectangular board, the resistivity of which was changed within a small domain of it. Then, the resistivity distribution of a CFRC sample with a circlar hole as the target was detected by the ERT system. Simulation and experimental results show that the reconstructed ERT image reflects the resistivity distribution or the resistivity change of CFRC structure well. Especially, a small change in resistivity can be identified from the reconstructed images in the simulation of dynamic ERT images.

Exploration on electrical resistance tomography in characterizing the slurry spatial distribution in cemented granular materials

This study investigated the application of electrical resistance tomography(ERT)in characterizing the slurry spatial distribution in cemented granular materials(CGMs).For CGM formed by self-flow grouting,the voids in the accumulation are only partially filled and the bond strength is often limited,which results in difficulty in obtaining in situ samples for quality evaluation.Therefore,it is usually infeasible to evaluate the grouting effect or monitor the slurry spatial distribution by a mechanical method.In this research,the process of grouting cement paste into high alumina ceramic beads(HACB)accumulation is reliably monitored with ERT.It shows that ERT results can be used to calculate the cement paste volume in the HACB accumulation,based on calibrating the saturation exponent n in Archie’s law.The results support the feasibility of ERT as an imaging tool in CGM characterization and may provide guidance for engineering applications in the future.

MEASUREMENT OF SOLID SLURRY FLOW VIA CORRELATION OF ELECTROMAGNETIC FLOW METER,ELECTRICAL RESISTANCE TOMOGRAPHY AND MECHANISTIC MODELLING

The study presented here was carried out to obtain the actual solids flow rate by the combination of electrical resistance tomography and electromagnetic flow meter. A new in-situ measurement method based on measurements of the Electromagnetic Flow Meters （EFM） and Electrical Resistance Tomography （ERT） to study the flow rates of individual phases in a vertical flow was proposed. The study was based on laboratory experiments that were carded out with a 50 mm vertical flow rig for a number of sand concentrations and different mixture velocities. A range of sand slurries with median particle size from 212 μm to 355 μm was tested. The solid concentration by volume covered was 5% and 15%, and the corresponding density of 5% was 1078 kg/m^3 and of 15% was 1238 kg/m^3. The flow velocity was between 1.5 m/s and 3.0 m/s. A total of 6 experimental tests were conducted. The equivalent liquid model was adopted to validate in-situ volumetric solids fraction and calculate the slip velocity. The results show that the ERT technique can be used in conjunction with an electromagnetic flow meter as a way of measurement of slurry flow rate in a vertical pipe flow. However it should be emphasized that the EFM results must be treated with reservation when the flow pattern at the EFM mounting position is a non-homogenous flow. The flow rate obtained by the EFM should be corrected considering the slip velocity and the flow pattern.

Distribution characteristics of holdups in a multi-stage bubble column using electrical resistance tomography

Based on the principle of chemical reaction engineering, the addition of perforated plates can improve the performance of conventional bubble column and decrease the backmixing behaviors. The distribution characteristics of gas holdup in a multi-stage bubble column embedded with five types of sieve plates and three types of tongue plates were studied using electrical resistance tomography （ERT）. The effects of superficial gas velocity and the geometric design of perforated plates on the gas holdup and its radial distribution above and below the plates of the bubble column were discussed. Experimental results show ERT is suitable as an online monitoring tool to provide useful information on the hydrodynamic param-eters of multi-stage bubble columns. With increasing superficial gas velocity, local gas holdup increases, and gas holdup below the plate increases with decrease of free area （%FA）, hole diameters or angle of tongue plates. ERT technique facilitates noninvasive and nonintrusive visualization of cross-sectional distribution of gas holdup in a bubble column.

Landslide monitoring in southwestern China via time-lapse electrical resistivity tomography

The dynamic monitoring of landslides in engineering geology has focused on the correlation among landslide stability,rainwater infiltration,and subsurface hydrogeology.However,the understanding of this complicated correlation is still poor and inadequate.Thus,in this study,we investigated a typical landslide in southwestern China via time-lapse electrical resistivity tomography（TLERT） in November 2013 and August 2014.We studied landslide mechanisms based on the spatiotemporal characteristics of surface water infiltration and flow within the landslide body.Combined with borehole data,inverted resistivity models accurately defined the interface between Quaternary sediments and bedrock.Preferential flow pathways attributed to fracture zones and fissures were also delineated.In addition,we found that surface water permeates through these pathways into the slipping mass and drains away as fissure water in the fractured bedrock,probably causing the weakly weathered layer to gradually soften and erode,eventually leading to a landslide.Clearly,TLERT dynamic monitoring can provide precursory information of critical sliding and can be used in landslide stability analysis and prediction.

Nonlinear inversion for electrical resistivity tomography based on chaotic DE-BP algorithm

Nonlinear resistivity inversion requires efficient artificial neural network(ANN)model for better inversion results.An evolutionary BP neural network(BPNN)approach based on differential evolution(DE)algorithm was presented,which was able to improve global search ability for resistivity tomography 2-D nonlinear inversion.In the proposed method,Tent equation was applied to obtain automatic parameter settings in DE and the restricted parameter Fcrit was used to enhance the ability of converging to global optimum.An implementation of proposed DE-BPNN was given,the network had one hidden layer with 52 nodes and it was trained on 36 datasets and tested on another 4 synthetic datasets.Two abnormity models were used to verify the feasibility and effectiveness of the proposed method,the results show that the proposed DE-BP algorithm has better performance than BP,conventional DE-BP and other chaotic DE-BP methods in stability and accuracy,and higher imaging quality than least square inversion.

Hydrate formation and distribution within unconsolidated sediment:Insights from laboratory electrical resistivity tomography

Laboratory visual detection on the hydrate accumulation process provides an effective and low-cost method to uncover hydrate accumulation mechanisms in nature.However,the spatial hydrate distribution and its dynamic evolutionary behaviors are still not fully understood due to the lack of methods and experimental systems.Toward this goal,we built a two-dimensional electrical resistivity tomography(ERT)apparatus capable of measuring spatial and temporal characteristics of hydrate-bearing porous media.Beach sand(0.05–0.85 mm)was used to form artificial methane hydrate-bearing sediment.The experiments were conducted at 1°C under excess water conditions and the ERT data were acquired and analyzed.This study demonstrates the utility of the ERT method for hydrate mapping in laboratory-scale.The results indicate that the average electrical conductivity decreases nonlinearly with the formation of the hydrate.At some special time-intervals,the average conductivity fluctuates within a certain scope.The plane conductivity fields evolve heterogeneously and the local preferential hydrate-forming positions alternate throughout the experimental duration.We speculate that the combination of hydrate formation itself and salt-removal effect plays a dominant role in the spatial and temporal hydrate distribution,as well as geophysical parameters changing behaviors during hydrate accumulation.

Mapping Subsurface Seepage Flow Patterns in Proximity to a Coal Combustion Residual Landfill Using Electrical Resistivity Tomography

Electrical resistivity tomography data were acquired in proximity to the coal combustion residual landfill in an effort to image and analyze seepage pathways through the shallow residual soil and underlying karsted limestone bedrock. The water table is at a depth of more than 45 m. The most prominent subsurface seepage pathways identified on the acquired electrical resistivity tomography data are located immediately adjacent to the toe of the landfill and are attributed to stormwater run-off. The moisture content of the limestone appears to decrease gradually with increasing distance from the toe of the landfill, suggesting there is also a horizontal component of moisture flow in the subsurface. Shallow limestone with higher moisture content generally underlies or is in close proximity to anthropogenic features such as drainage ditches and clay berms that are designed to channel run-off. At one location, electrical resistivity tomography data were acquired along essentially the same traverse at different times of the year, and the resistivity of shallow limestone overall was lower on the data acquired after heavy rains.

Application of 3D Electrical Resistivity Tomography for Diagnosing Leakage in Earth Rock-Fill Dam

The leakage occurs during operation of the dam in Liuhuanggou reservoir. It’s a threat to the safety of the people’s lives and property in downstream. In order to eliminate the hidden danger of reservoir, ensure the safety of the dam, play better the function of flood control and water storage of the reservoir etc., we apply the 3D electrical resistivity tomography detecting technology and volume rendering image processing technology, make the measurement in field, process the data and combine the field survey to find out the leakage channels inside the dam. The results show that the 3D resistivity images appear the low resistivity zone corresponding with the leakage channels. There are two main leakage channels that come from different location inside the dam. It is feasible to diagnose the leakage in earth rock-fill dam by applying 3D electrical resistivity tomography.

Numerical Simulation Study on the Detection of Weak Structural Plane of Rock Slope by Using 3D Electrical Resistivity Tomography

The weak structure plane is an important factor affecting the stability of rock slope, and detecting the spatial structure of the weak structural plane is beneficial to analyze the stability of the slope and estimate the quantity of the landslide. Based on 3D electrical resistivity tomography, a model of rock slope with weak structure plane is established, and the characteristics of three-dimensional resistivity imaging of weak structure plane under different ground water conditions are simulated. The results show that the weak structural plane has a better reflection in 3D electrical resistivity tomography;the distribution of weak structural plane of 3D resistivity imaging can be roughly determined under different ground water conditions;the three-dimensional electrical resistivity tomography is feasible in the detection of weak structural plane of rock slope.

Electrical geophysical evaluation of susceptibility to flooding in University of Nigeria, Nsukka main campus and its environs, Southeastern Nigeria

Flooding occurs when rainfall exceeds the absorption capacity of soil and causes significant environmental consequences.In this study,electrical resistivity techniques were employed to assess the flood susceptibility of the study area by examining variations in electrical properties.Prior to flooding,Vertical Electrical Sounding(VES)and Electrical Resistivity Tomography(ERT)profiles were conducted to determine the variations in resistivity within subsurface lithologies exposed to the injected current.The injected current penetrated the subsurface units characterised by resistivity ranging from 190.5Ω·m to 6,775.7Ω·m,42.3Ω·m to 7,297.4Ω·m,and 320.2Ω·m to 24,433.3Ω·m in the first,second and third layers,respectively.These layers were identified as lateritic topsoil,medium-coarse brownish grained sand,and coarse pebbly blackish sand,respectively.The calculated reflection coefficients between layers 1,2,and 3 reveal alternation in layers with values ranging from−0.04 to 0.66 and 0.36 to 0.95 for and,respectively.The transverse resistivity,longitudinal resistivity and anisotropy ranged from 243.59Ω·m to 24,115.42Ω·m,199.61Ω·m to 14,950.76Ω·m,and 1.02 to 2.14.Models derived from the ERT profiles reveal variations in resistivity,pinpointing areas of low resistivity which correspond to waterlogged and impermeable layers.The result of this study underscores the importance of integrated resistivity techniques in the study of floods,as it provides valuable insights into flood behaviour,and subsurface dynamics.

Application of geophysical methods in fine detection of urban concealed karst:A case study of Wuhan City,China

The construction of modern livable cities faces challenges in karst areas,including ground collapse and engineering problems.Wuhan,with a population of 13.74×10^(6) and approximately 1161 km^(2)of soluble rocks in the urban area of 8569.15 km^(2),predominantly consists of concealed karst areas where occasional ground collapse events occur,posing significant threats to underground engineering projects.To address these challenges,a comprehensive geological survey was conducted in Wuhan,focusing on major karstrelated issues.Geophysical methods offer advantages over drilling in detecting concealed karst areas due to their efficiency,non-destructiveness,and flexibility.This paper reviewed the karst geological characteristics in Wuhan and the geophysical exploration methods for karst,selected eight effective geophysical methods for field experimentation,evaluated their suitability,and proposed method combinations for different karst scenarios.The results show that different geophysical methods have varying applicability for karst detection in Wuhan,and combining multiple methods enhances detection effectiveness.The specific recommendations for method combinations provided in this study serve as a valuable reference for karst detection in Wuhan.

Integrated Geoelectrical Resistivity Method for Environmental Assessment of Landfill Leachate Pollution and Aquifer Vulnerability Studies

Leachate plumes from landfills are a major source of pollution in Nigeria, especially in urban areas. Assessing leachate contamination in the subsoil is considered a complex process that needs detailed field measurement to accurately define the extent of contamination. To ascertain the extent of pollution of the subsoil and groundwater sources which were reportedly contaminated by leachate plumes from an old dumpsite located in Osubi town, an integrated geo-electrical method involving 1-D vertical electrical sounding (VES) and 2-D, 3-D ERT techniques were employed. Orthogonal set of 2-D apparent resistivity data was collected in a 100 × 50 m2 rectangular grid around the dumpsite, using the Wenner array. Two years later, three (3) 2-D resistivity imaging profiles were also recorded in time-lapse mode at the dumpsite to monitor the possible effects of attenuation on the leachate over time. Ten (10) VES data were also acquired and used along with the 2-D imaging data. 2-D apparent resistivity data were inverted with Dipprowin software program. The orthogonal set of 2-D lines of apparent resistivity was merged into 3-D data and inverted with RES3DINV program to create a 3-D subsurface resistivity model. Geological models observed from 2-D and 3-D resistivity inversion revealed low resistivity values in the order ρ Ω·m which is indicative of leachate plumes in the saturation zone (pore water). The 2-D resistivity-depth sections imaged low resistivity leachate plumes at the near surface (<5 m) to a depth of 25.0 m, while 3-D inversion depth slices imaged leachate contaminant within the first, second and third layers at depth ranging from 0.00 - 2.50 m, 2.50 - 5.38 m and 5.38 - 8.68 m respectively. Thus, leachate contamination clearly increased with depth beyond the depth of first and second aquifers in the area which implies that available groundwater for domestic use is already contaminated with leachate from the dumpsite. Leachate contaminant-depth map estimated for the second geoelectric layers for VES 2, 3, 4, 7, 8, 9, and 10 shows that the second layer has been invaded completely by leachate contamination up to 6.5 m depth. 2-D apparent resistivity data acquired two years after show lower resistivity anomalies of the leachate plume caused by time-lapse attenuation effect on the observed resistivity of the leachate. This indicates that the leachate plume has become more conductive and toxic to the environment. The Longitudinal conductance map of the area shows that the aquifer protective capacity of this area is weak (0.1 - 0.19 Mho) thus, aquifers in the area are prone to pollution from the dumpsite. The three techniques used in this study (2-D, 3-D ERT and 1-D VES) fitly provided crucial information on the degree of contamination caused by the landfill leachate plume. Therefore, it is advisable to implement an environmental remediation and leachate management program.

Determination of rock mass integrity coefficient using a non-invasive geophysical approach

Determination of rock mechanical parameters is the most important step in rock mass quality evaluation and has significant impacts on geotechnical engineering practice.Rock mass integrity coefficient(KV)is one of the most efficient parameters,which is conventionally determined from boreholes.Such approaches,however,are time-consuming and expensive,offer low data coverage of point measurements,require heavy equipment,and are hardly conducted in steep topographic sites.Hence,borehole approaches cannot assess the subsurface thoroughly for rock mass quality evaluation.Alternatively,use of geophysical methods is non-invasive,rapid and economical.The proposed geophysical approach makes useful empirical correlation between geophysical and geotechnical parameters.We evaluated the rock mass quality via integration between KV measured from the limited boreholes and inverted resistivity obtained from electrical resistivity tomography(ERT).The borehole-ERT correlation provided KV along various geophysical profiles for more detailed 2D/3D(two-/three-dimensional)mapping of rock mass quality.The subsurface was thoroughly evaluated for rock masses with different engineering qualities,including highly weathered rock,semi-weathered rock,and fresh rock.Furthermore,ERT was integrated with induced polarization(IP)to resolve the uncertainty caused by water/clay content.Our results show that the proposed method,compared with the conventional approaches,can reduce the ambiguities caused by inadequate data,and give more accurate insights into the subsurface for rock mass quality evaluation.

Oil–water two-phase flow pattern analysis with ERT based measurement and multivariate maximum Lyapunov exponent

Oil–water two-phase flow patterns in a horizontal pipe are analyzed with a 16-electrode electrical resistance tomography(ERT) system. The measurement data of the ERT are treated as a multivariate time-series, thus the information extracted from each electrode represents the local phase distribution and fraction change at that location. The multivariate maximum Lyapunov exponent(MMLE) is extracted from the 16-dimension time-series to demonstrate the change of flow pattern versus the superficial velocity ratio of oil to water. The correlation dimension of the multivariate time-series is further introduced to jointly characterize and finally separate the flow patterns with MMLE. The change of flow patterns with superficial oil velocity at different water superficial velocities is studied with MMLE and correlation dimension, respectively, and the flow pattern transition can also be characterized with these two features. The proposed MMLE and correlation dimension map could effectively separate the flow patterns, thus is an effective tool for flow pattern identification and transition analysis.

Field Sensing Characteristic Research of Carbon Fiber Smart Material

In order to research the field sensing characteristic of the carbon fiber smart material, the Tikhonov regularization principle and the modified Newton-Raphson(MNR) algorithm were adopted to solve the inverse problem of the electrical resistance tomography(ERT). An ERT system of carbon fiber smart material was developed. Field sensing characteristic was researched with the experiment. The experimental results show that the specific resistance distribution of carbon fiber smart material is highly consistent with the distribution of structural strain. High resistance zone responds to high strain area, and the specific resistance distribution of carbon fiber smart material reflects the distribution of sample strain in covering area. Monitoring by carbon fiber smart material on complicated strain status in sample field domain is realized through theoretical and experimental study.

Design of ERT system

A new electrical resistance tomography (ERT) system, based on the bi-directional current pulse technique, is de- veloped. Polarization effects at the electrodes are eliminated. During each half cycle of the excitation process, direct current (DC) is used as the excitation source and filtering is not needed. Moreover, using optimized data collection protocol, the number of current injections for a 16-electrode system is reduced to 14 for 104 independent readings of an image. Experimental results showed that the system is effective using the sensitivity coefficient algorithm for image reconstruction.