The Research On The Optimal Design And Excitation Mode Of Direct Three Dimensional ECT System

On line detection of two-phase flow parameters is very important for industrial production process.Due to the complex flow process,it’s difficult to measure accurately.ECT(Electrical Capacitance Tomohgraphy),which has the advantages of non-invasive,high security and visualization,is widely studied and applied in two-phase flow detection fields..The traditional two-dimensional ECT and indirect three-dimensional ECT systems can not obtain the three-dimensional information such as geometric shape,spatial location.It can not measure accurate or realize high-quality three-dimensional visualization detection.Aiming at these problems,it is necessary to research on direct three-dimensional ECT technology.This thesis was set in the ECT technology,the multi-physical field finite element analysis software COMSOL is taken as research platform.The three-dimensional ECT sensor as the research object.Account of the poor reconstruction image quality,the three-dimensional excitation measurement mode was explored and new kinds of multi-electrode excitation modes are proposed.A multi-objective optimization design of the three-dimensional ECT sensor structure was proposed which made use of simulatiom and physical experiments.The normalization algorithm was made a deep study and improved.A Landweber iterative algorithm with automatic threshold adjustment was proposed.The main work of this thesis is showed as follow:(1)The rapid modeling of ECT system was realizded based on multi-physical field software and MATLAB script file.The method of finite element was discussed to calculate capacitance value and distribution of sensitive.The forward problem of 3D ECT system was completed.(2)Aiming at the disadvantage in traditional single-electrode excitation mode,multi-electrode excitation modes were proposed to improve the uniformity of sensitive field distribution,increase the amount of projection data and improve the quality of reconstructed image.(3)Considering the uncertainty of three-dimensional ECT sensor structure,the advantages and disadvantages of several ECT sensor structures are analyzed based on finite element simulation.The sensor model was determined.The influences of structural parameters on sensor sensitivity field and optimization index were analyzed in detail on sensor.The critical structural parameters were determined.According to the imaging requirement,the parameters of reconstructed image are proposed as the optimization objective.The multi-objective optimization design of sensor structure was realized by response surface method.The correlation coefficient of reconstruction image was increased by about 10%after optimization.(4)In view of the fact that the two-dimensional imaging and interpolation algorithms can not accurately reflect the distribution,the normalization algorithm of 3D projection data is improved.Based on the study of LBP algorithm and Landweber iteration algorithm,a Landweber iterative algorithm with automatic threshold adjustment was proposed.Experiments show that the correlation coefficient of reconstruction image was increased by about 10%,even above 15%.(5)In order to verify the actual measurement,gas-liquid two phase flow in vertical pipeline was established in the condition of multi-physical coupling(flow field-electrostatic field)by COMSOL software.The out data of three-dimensional ECT system were obtained and studied according to flow patterns.The optimized sensor structure,improved algorithm and excitation mode are validated by comparing the quality of reconstructed image.The ECT sensor was made according to the optimal design results for experimental verification in aboratory conditions.The output of physical experiment was consistent with simulation output,which improved that three-dimensional ECT can meet the need of actual measurement.