Electrical Capacitance Tomography And Its Applications In Two-Phase Flow Measurements

Electrical capacitance tomography(ECT)technology is a process tomography technology based on capacitance sensitive fields,which can use the measured capacitance values by the capacitance sensor to reconstruct distribution images of different dielectrics in the measured field,this technology enables visualization measurement the internal state of two-phase or multi-phase flows.ECT technology is one of the popular research techniques in the field of process tomography because of simple structure,low cost and no radiation,and it is now widely used in agricultural production,geological exploration,aerospace and other fields.This thesis explores and improves ECT image reconstruction algorithms,and analyses practical application in two-phase flow measurement according8-electrode electrical capacitance tomography system,and aims to reduce the number of iteration steps,and promotes the speed of stable convergence and the image reconstruction quality.The main works are as follows:(1)This thesis elaborates on the system structure of electrical capacitance tomography technology,which mainly includes three parts: capacitance sensor unit,data acquisition unit,and image reconstruction unit,and introduces the composition of each part and the current research direction;And introduces the principle of electrical capacitance tomography technology and two main problems: forward problem and inverse problem;The calculation of the sensitivity matrix is derived at length and the key information of the ECT image reconstruction is specified.(2)The principles of several traditional image reconstruction algorithms in electrical capacitance tomography are mainly summarized.Based on this,four flow patterns named laminar flow,annular flow,core flow and bubble flow are reconstructed.The subjective evaluation method is used to roughly compare and analyze the reconstructed image quality of different algorithms;then the relative error,correlation coefficient and comprehensive score are introduced as objective evaluation indexes to quantitatively describe the ability of different algorithms to reconstruct images.And combination of both subjective and objective evaluation methods provides an evaluation basis for comparing the quality of reconstructed images.(3)The ECT image reconstruction is achieved based on numerical simulation experiments,the image reconstruction speed and quality of different algorithms are compared and analyzed from the perspective of both subjective and objective evaluation,respectively.The results show that the Landweber algorithm has relatively low computational complexity,but the number of iteration steps is relatively long,and relatively poor stability and low image reconstruction accuracy,it still has the need to improve.So,by analyzing the principle of Landweber algorithm,the residual matrix is constructed,and the weight factor is added to make it reach the stable convergence condition,and the Landweber algorithm based on the weight factor is obtained.(4)Aiming at the ill-posedness of ECT inverse problem,several improved algorithms are proposed according to different ideas such as double loop,gradient acceleration,homotopy perturbation regularization.The numerical simulation experiment of ECT image reconstruction is conducted by selecting four common flow patterns:laminar flow,annular flow,core flow and bubble flow.The results show that each of the improved algorithms has their own advantages,which can not only ensure the stability of the reconstructed flow pattern results,but also significantly reduce the number of iteration steps and improve the speed of stable convergence,at the same time,they are insensitive to initial values and have certain anti-noise performance.These are beneficial for industrial applications of two-phase flow measurement,and reflect practical application value to a certain extent.