High-precision Extraction Of Electrical Impedance Tomography Objects And Three-dimensional Visualisation Of Two-phase Flow

Two-phase flow is widely used in many industrial processes,such as petroleum,chemical,energy,power and pharmaceutical.The accurate measurement and high-quality visualisation of two-phase flow are of great significance for understanding and predicting fluid dynamics,process operation and control,and analysing and optimising flow equipment.Due to the interaction of many complex factors,such as the phase interface,wave phenomena and the fluid spatial structure,the phase distribution and flow pattern in the two-phase flow are complex and variable.Therefore,the detail description of the flow process and mechanism,as well as the accurate flow measurement and hgh-quailty visualisation meet great challenges for engineers and researchers.Based on the analysis and review of two-phase measurement and visualisation tecniques,the electrical impedance tomography(EIT)is employed to conduct series of studies.The highprocision extraction of objects and three dimensional visualisation of two-phase flow are proposed to improve the object measurement accuracy and enhance the visual performance of EIT measurement results in displaying flow pattern phenomena and revealing flow mechanisms.The main work and innovations of this research are as follows:According to the EIT basic theories,the influence of EIT electrode size on electric field characteristics is discussed and analyze.Aiming at the problem that the point-electrode model affects the accuracy of finite element simulation,an EIT finite element simulation based on electrode-nodes grouping model is proposed.The EIT forward and inverse processes are optimised,which effectively reduces the electrode size in EIT finite element simulation and improves the accuracy of the EIT forward solution and the sensitivity matrix.Simultaneously,the common image reconstruction algorithms are evaluated Therefore,an appropriate image reconstruction algorithm should be selected for meeting the reconstruction target and requirements in EIT applications.Aiming at the significant reconstruction artifacts in the EIT reconstructed image,a highprecision object extraction method base on size projection algorithm and measurement parameters is proposed.Here,the EIT measurement parameters are introduced into the object extraction process with multi-step optimization,where the high-precision quantitative information is obtained,such as the object boundary,size in EIT reconstruction image.Simulation,static and dynamic measurement experiments are conducted and verify that the proposed size projection method can effectively improve the accuracy of object extraction.For the demand of gas-liquid two-phase flow 3D visualisation and the basis of object measurement,a 3D visualisation method based on the fusion of size projection and bubble mapping is proposed,which can display the size,shape and position information of bubbles in two-phase flow.It greatly improves the bubbles visualisation performance in gas-liquid flow.It has a strong visual enhancement effect for the explanation of flow regimes and flow mechanism based on EIT measurement.The gas-liquid flow experiments both in horizontal and vertical pipelines are conducted to verify the efficiency of the proposed method.And the effects of key parameters are also discussed.In addition,the performance of the online EIT algorithm on gas-liquid flow measurement is also analyzed and evaluated.The results show that the sensitivity back-projection algorithm is suitable for horizontal gas-liquid flow measurement,while the modified sensitivity back-projection algorithm is suitable for vertical gas-liquid flow measurement.For the measurement and monitoring of solid-liquid flow,a solution for visually monitoring solid-liquid flow using a dual-plane EIT system is proposed,which can measure the solid volumetric fraction and solid axial velocity,and can provide the visually monitoring with the cross-sectional solid phase distribution.The results of solid-liquid flow experiment initialy verify the feasibility of the proposed method.The visualisation results are consistent with the photo recorded by a high-speed camera through a transparent section,and the experimental phenomenon found is consistent with the solid-liquid flow theory.