Study On Two-Phase Flow Detection Method Based On Ultrasonic Tomography

The requirement of multiphase detection widely exist in industrial fields.According to the number of classes involved in the flow multiphase flow can be divided into two-phase flow and three-phase flow,of which two-phase flow is the most commom.In the gas/liquid two-phase flow system,because of the interaction between gas and liquid,the existence of phase interface which is varying randomly in time and space,resulting in two-phase flow system has a complex flow characteristics,so its parameter detection is very difficult.Ultrasonic tomography is a non-destructive testing technique,which can be used to continuously provide two-dimensional visualization information of the two-phase flow profile.The post-processing is used to extract the relevant characteristic parameters of the measured two-phase fluid,which has important engineering application value.The transmission-mode ultrasonic tomography is used to detect gas/liquid two-phase flow's indicators such as flow pattern and gas content in this dissertation.The main research works include:(1)Research on UT system imaging algorithm for gas/liquid two-phase flow detection.In this paper,four imaging algorithms with potential application value in industrial inspection field are studied for detecting gas/liquid two-phase flow under weak scattering conditions.First,it is ellipse imaging algorithm,which is widely used in the field of non-destructive testing of plate materials.This dissertation attempts to introduce it into UT detection,and analyze its advantages and disadvantages.Then,the attenuated linear back projection algorithm is proposed,and its imaging effect and applicable reconstruction flow pattern are analyzed.After that,aiming at the linear back projection algorithm based on ray theory for the current mainstream application,an improved fan-shaped linear back projection algorithm is proposed.Because of the different methods of constructing the sensitivity matrix,the influence to the reconstructed results of the two algorithms is obvious.For this reason,the imaging effect of the two algorithms are compared quantitatively.(2)Quantitative evaluation of imaging results of different flow patterns.It is one of the main contents of this dissertation to quantitatively evaluate the reconstructing results of the same flow pattern rebuilded using different reconstruction algorithms.The reconstructed results are quantitatively evaluated by four parameters,namely,image correlation coefficient,position error,shape deformation and resolution,which were introduced by this paper,and the applicability of the four reconstruction algorithms to reconstruct different flow patterns is given.(3)Comparative study on the different threshold processing method.In order to improve the image quality,two kinds of threshold processing methods,namely,hybrid reconstruction algorithm(HR)and adaptive threshold filtering algorithm(ATF),are used to process the original imaging results.The effect of the two methods is compared,and it is found that the ATF method is superior to the HR method.(4)Research on optimization of sensor number in UT system.There are many parameters that can affect the image quality in UT system,of which the most important is the number of sensors.For this reason,different sets of sensor arrays are used to optimize the imaging results of different flow patterns,and the number of optimal sensors was found to be 32.