Research On Irregular Cross-Section ECT Sensor And Image Reconstruction

Electrical capacitance tomography(ECT)is a process tomography technology based on capacitance sensing mechanism,which can visually measure the distribution of media with different dielectric constants in a closed pipeline or reactor.This technology needs to install the measuring plate on the surface of the insulated pipe to form a capacitance sensor;The capacitance between each pair of polar plates is obtained by using a micro capacitance measuring circuit and a data acquisition system;Use appropriate reconstruction algorithm to reconstruct the measured medium distribution.This technology has the advantages of non-invasion,low cost,good safety and so on,and has a broad application prospect in chemical fluidized bed,oil pipeline,coated particle reactor and other fields.At present,the cross section of pipeline or reactor measured by ECT technology is usually circular.However,in the industrial process,there are a large number of pipelines or equipment with irregular cross sections,such as the multi-ring inclined hole fluidized bed with small inclination,complex angle and structure for preparing nuclear fuel coated particles.When ECT system is used to image irregular cross-section pipes,the gap between the irregular pipes and the inner wall of the sensor is usually filled with materials with known dielectric constant.Because of high temperature,corrosion and other reasons,the same gap filling problem exists in industrial occasions where the measuring plate cannot be installed on the outer wall of the pipeline or reactor.Taking hexagonal cross-section as an example,this paper studies the ECT sensor with irregular cross-section and image reconstruction.The main work and achievements of this paper are as follows:1.Taking hexagonal pipe as an example,two kinds of ECT sensor models with irregular cross-section,direct installation and filling,are established.The sensitive field of these two sensors is analyzed and the influence of sensor parameters on their performance is studied.The parameters of two kinds of ECT sensors with irregular cross-section used in this paper are determined.2.A complete finite element analysis model of filled ECT sensor is established.Different from the conventional sensitivity calculation method and empty-full-field calibration method,the adverse effects of pipe wall and filling area on reconstruction quality are reduced.By using the known dielectric constant of the filled area and the decomposition of the sensitivity matrix,a reduced-dimension ECT forward problem model is established,which reduces the ill-posed of the inverse problem.The improved Landweber iteration method is used to solve the inverse problem.The simulation results show that the proposed method can obviously improve the reconstruction quality.3.The image reconstruction of the direct-mounted sensor is studied by finite element simulation,and the image reconstruction results of the two sensors are compared and analyzed.4.Self-made filled ECT sensor,combined with the capacitance data acquisition system in the laboratory,established an experimental system of ECT image reconstruction with irregular cross section.Using this system,the effectiveness of the proposed method is verified by experiments.