Study On Modeling And Optimal Design Of Capacitively Coupled Electrical Resistance Tomography System

Electrical resistance tomography (ERT) technique is one of the most important process tomography (PT) techniques. Compared with other PT techniques, ERT has advantages including simple construction, high speed response, low cost, etc. ERT has a broad application prospect in the research field of parameters measurement of two-phase flow.However, the electrodes in conventional ERT sensor are directly in contact with the fluid, which will lead to polarization effect and electrochemical erosion effect. These drawbacks limit the practical application of conventional ERT in industry. Based on capacitively coupled contactless conductivity detection (C4D) technique, a new kind of ERT named capacitively coupled ERT (CCERT) technique is proposed by our research group. In the new CCERT sensor, the electrodes of CCERT sensor are mounted around outer surface of the pipe, therefore, the polarization effect and the electrochemical effect can be avoided. Preliminary work has been performed which has verified the feasibility of applying the C4D technique to PT. However, due to the difference between CCERT and conventional ERT, the current research experience and results of the conventional ERT can't be applied to CCERT directly and more research works should be undertaken, such as theoretical analysis and modeling, study on criteria of CCERT sensor design and image reconstruction, etc. The main focus of the research work is to study the modeling and optimal design of the CCERT sensor. Meanwhile, preliminary research on image reconstruction is also performed. A CCERT optimized prototype is developed based on the obtained optimized results and real-time image reconstruction experiments are carried out. The main works and innovation points are listed as follows:(1) The mathematical model of the CCERT sensor is established, and the effectiveness of the equivalent circuit (the series of resistance and capacitance between excitation and detection electrodes) is verified by simulation in 2D and 3D electromagnetic field based on finite element method.(2) To reduce the influence of the stray capacitance formed from the outer space of the pipe, the measurement performance of CCERT sensor by installing the radial electrodes is investigated. The experiment results show that the influence to the measurements caused by the radial electrodes is much larger than that caused by the stray capacitances, so this construction is not recommended.(3) To reduce the difficulty of the design of data acquisition unit and improve the measurement sensitivity, the physical and geometrical parameters of CCERT sensor are optimized. The optimization criteria obtained from the simulation results are smaller thickness of the pipe wall, higher permittivity of the pipe wall and larger sensor electrode angles.(4) The CCERT prototype is designed based on the optimized criteria, and real-time image reconstruction experiments are carried out. The sensitivity field needed by the image reconstruction is studied by simulation and the LBP algorithm for the image reconstruction is applied to the CCERT system. The results show that the reconstructed image can show the correct positions of the objects in the sensitive zone. The results also show that the modeling and the optimal design of CCERT sensor is effective, and the sensitivity field is practical.