Benyuan Sun

Liquid Film Thickness Estimation using Electrical Capacitance Tomography

Abstract In air/oil lubrication systems, the flow parameters, e.g., flow pattern, liquid film thickness, and air/oil flow rate, are of great importance to the transportation efficiency. In most cases, the on-going two-phase flow is annular flow with the oil moving along the tube wall and the air travelling at high speed in the center. This usually results in the formation of a thin oil film, the thickness of which is a key parameter determining the efficiency of the lubrication system. As the oil film thickness of the on-going air/oil flow varies dynamically, there is actually no applicable method for a non-intrusive test. In this paper, the use of electrical capacitance tomography (ECT) to investigate the air/oil flow has been studied. Capacitance measurements are made from an externally mounted electrode array in a non-invasive and non-intrusive manner. Both average and distributed oil film thicknesses can be calculated from the reconstructed ECT images. Simulation and experimental results show that the ECT technique can provide satisfactory results of online oil film thickness estimation

A review on image reconstruction algorithms for electrical capacitance/resistance tomography

Purpose Electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) are promising techniques for multiphase flow measurement due to their high speed, low cost, non-invasive and visualization features. There are two major difficulties in image reconstruction for ECT and ERT: the “soft-field”effect, and the ill-posedness of the inverse problem, which includes two problems: under-determined problem and the solution is not stable, i.e. is very sensitive to measurement errors and noise. This paper aims to summarize and evaluate various reconstruction algorithms which have been studied and developed in the word for many years and to provide reference for further research and application. Design/methodology/approach In the past 10 years, various image reconstruction algorithms have been developed to deal with these problems, including in the field of industrial multi-phase flow measurement and biological medical diagnosis. Findings This paper reviews existing image reconstruction algorithms and the new algorithms proposed by the authors for electrical capacitance tomography and electrical resistance tomography in multi-phase flow measurement and biological medical diagnosis. Originality/value The authors systematically summarize and evaluate various reconstruction algorithms which have been studied and developed in the word for many years and to provide valuable reference for practical applications.

Online monitoring of oil film using electrical capacitance tomography and level set method

In the application of oil-air lubrication system, electrical capacitance tomography (ECT) provides a promising way for monitoring oil film in the pipelines by reconstructing cross sectional oil distributions in real time. While in the case of small diameter pipe and thin oil film, the thickness of the oil film is hard to be observed visually since the interface of oil and air is not obvious in the reconstructed images. And the existence of artifacts in the reconstructions has seriously influenced the effectiveness of image segmentation techniques such as level set method. Besides, level set method is also unavailable for online monitoring due to its low computation speed. To address these problems, a modified level set method is developed: a distance regularized level set evolution formulation is extended to image two-phase flow online using an ECT system, a narrowband image filter is defined to eliminate the influence of artifacts, and considering the continuity of the oil distribution variation, the detected oil-air interface of a former image can be used as the initial contour for the detection of the subsequent frame; thus, the propagation from the initial contour to the boundary can be greatly accelerated, making it possible for real time tracking. To testify the feasibility of the proposed method, an oil-air lubrication facility with 4 mm inner diameter pipe is measured in normal operation using an 8-electrode ECT system. Both simulation and experiment results indicate that the modified level set method is capable of visualizing the oil-air interface accurately online.

An ECT/ERT dual-modality sensor for oil-water two-phase flow measurement

This paper presents a new sensor for ECT/ERT dual-modality system which can simultaneously obtain the permittivity and conductivity of the materials in the pipeline. Quasi-static electromagnetic fields are produced by the inner electrodes array sensor of electrical capacitance tomography (ECT) system. The results of simulation show that the data of permittivity and conductivity can be simultaneously obtained from the same measurement electrode and the fusion of two kinds of data may improve the quality of the reconstructed images. For uniform oil-water mixtures, the performance of designed dual-modality sensor for measuring the various oil fractions has been tested on representative data and the results of experiments show that the designed sensor broadens the measurement range compared to single modality.

Modified sparse regularization for electrical impedance tomography

Electrical impedance tomography (EIT) aims to estimate the electrical properties at the interior of an object from current-voltage measurements on its boundary. It has been widely investigated due to its advantages of low cost, non-radiation, non-invasiveness, and high speed. Image reconstruction of EIT is a nonlinear and ill-posed inverse problem. Therefore, regularization techniques like Tikhonov regularization are used to solve the inverse problem. A sparse regularization based on L1 norm exhibits superiority in preserving boundary information at sharp changes or discontinuous areas in the image. However, the limitation of sparse regularization lies in the time consumption for solving the problem. In order to further improve the calculation speed of sparse regularization, a modified method based on separable approximation algorithm is proposed by using adaptive step-size and preconditioning technique. Both simulation and experimental results show the effectiveness of the proposed method in improving the image quality and real-time performance in the presence of different noise intensities and conductivity contrasts.

Optimal distance of multi-plane sensor in three-dimensional electrical impedance tomography

Abstract Electrical impedance tomography (EIT) is a visual imaging technique for obtaining the conductivity and permittivity distributions in the domain of interest. As an advanced technique, EIT has the potential to be a valuable tool for continuously bedside monitoring of pulmonary function. The EIT applications in any three-dimensional (3 D) field are very limited to the 3 D effects, i.e. the distribution of electric field spreads far beyond the electrode plane. The 3 D effects can result in measurement errors and image distortion. An important way to overcome the 3 D effect is to use the multiple groups of sensors. The aim of this paper is to find the best space resolution of EIT image over various electrode planes and select an optimal plane spacing in a 3 D EIT sensor, and provide guidance for 3 D EIT electrodes placement in monitoring lung function. In simulation and experiment, several typical conductivity distribution models, such as one rod (central, midway and edge), two rods and three rods, are set at different plane spacings between the two electrode planes. A Tikhonov regularization algorithm is utilized for reconstructing the images; the relative error and the correlation coefficient are utilized for evaluating the image quality. Based on numerical simulation and experimental results, the image performance at different spacing conditions is evaluated. The results demonstrate that there exists an optimal plane spacing between the two electrode planes for 3 D EIT sensor. And then the selection of the optimal plane spacing between the electrode planes is suggested for the electrodes placement of multi-plane EIT sensor.

Level set based image segmentation for oil film monitoring using ECT

In air/oil lubrication system, the flow regime and oil film thickness are significant for lubrication efficiency and can only be monitored online. Electrical capacitance tomography (ECT) provides a promising strategy for monitoring air/oil two phase flow in the pipelines by reconstructing cross sectional oil distributions with good real-time performance. While the low spatial resolution of ECT reconstructions has seriously influenced the visualization of the interface of oil and air. To apply ECT to oil film monitoring and film thickness estimation, a modified level set-based image segmentation technique is introduced: a distance regularized level set evolution (DRLSE) formulation is adopted to accelerate the computation process while guaranteeing the stability of the evolution, and since the interface propagates in different directions (inwards or outwards) at different regions of the cross section, the image is divided into 4 regions, and contour evolutions are carried out in different regions respectively using local void fractions to determine the direction of evolution (inward or outward). Experiment is carried out using an 8-electrode ECT system installed on an air/oil lubrication facility, the results demonstrate that the proposed method is capable of visualizing the air/oil interface online.

Early lung cancer identification based on ERT measurements

Early lung cancer identification is a very promising way to prevent and cure lung cancer. The current lung cancer identification method based on the X-ray computed tomography difficultly identify the early lung cancer, while the electrical resistance tomography (ERT) technique has potential to overcome the problem by visualizing the human respiratory system. The original ERT system has poor quality of reconstructed images. One feasible method to improve image quality is to incorporate prior information into ET imaging process. In this paper, we first extract the prior information from a group of patients CT images (e.g., the general structure, conductivity distributions of human respiratory, and etc.). Then a new ERT imaging method is proposed based on the prior information and the existing Tikhonov regularization method. Experimental results demonstrate that the proposed method can greatly enhance the spatial resolution of ERT imaging and make the lung cancer identification better.

Patch-based sparse reconstruction for electrical impedance tomography

Purpose Electrical impedance tomography (EIT) is a technique for reconstructing the conductivity distribution by injecting currents at the boundary of a subject and measuring the resulting changes in voltage. Image reconstruction for EIT is a nonlinear problem. A generalized inverse operator is usually ill-posed and ill-conditioned. Therefore, the solutions for EIT are not unique and highly sensitive to the measurement noise. Design/methodology/approach This paper develops a novel image reconstruction algorithm for EIT based on patch-based sparse representation. The sparsifying dictionary optimization and image reconstruction are performed alternately. Two patch-based sparsity, namely, square-patch sparsity and column-patch sparsity, are discussed and compared with the global sparsity. Findings Both simulation and experimental results indicate that the patch based sparsity method can improve the quality of image reconstruction and tolerate a relatively high level of noise in the measured voltages. Originality/value EIT image is reconstructed based on patch-based sparse representation. Square-patch sparsity and column-patch sparsity are proposed and compared. Sparse dictionary optimization and image reconstruction are performed alternately. The new method tolerates a relatively high level of noise in measured voltages.

An ECT/ERT dual-modality system based on an internal electrode sensor

Electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) are the two most developed ET methods nowadays. ERT is suitable to measure the two-phase flow in which conductive medium is taken as the continuous phase, while ECT is suitable to measure the two-phase flow in which non-conducting medium is taken as the continuous phase. In order to broaden the measurement range, generally combing the both ECT and ERT modalities to form an ECT/ERT dual-modality system is used. Therefore, this paper presents a novel unified sensor which can operate in both ECT and ERT modality and a series of experiments for oil-water two phase flow measurement are studied based on this dual-modality sensor with the inner electrode. The results demonstrate that the dual-modality system can operate stably, flexibly, and expand the measurement range.