A New Contactless Impedance Sensor For Gas-liquid Two-phase Flow Parameter Measurement

Gas-Liquid two-phase flow widely exists in the nature and many industrial processes,such as petroleum,energy,chemical,etc..Its parameter measurement is of great significance but faces great difficulties.The equivalent conductivity detection method of gas-liquid two-phase flow is important because of its simple structure,low cost,fast response and high safety.There are problems of electrode polarization and electrochemical erosion in conventional contact conductivity detection.The capacitance coupled contactless conductivity detection(C4D)technique proposed in recent years provides an effective way to solve the mentioned problems.However,the purpose of existing C4D sensors is to obtain the conductance information of the fluid,that is,only the real part or amplitude information of the fluid resistance is obtained.When it is applied to gas-liquid two-phase flow,the acquisition and utilization of the measurement information is incomplete.In order to obtain the whole impedance information of gas-liquid two-phase flow,a new contactless impedance sensor is developed on the basis of the C4D technique,and hence to apply to flow pattern identification and void fraction measurement of gas-liquid two-phase flow.The main works and innovations of this thesis are as follows:(1)A contactless impedance measurement method based on a radial two-electrode sensor is proposed to obtain the whole impedance information of gas-liquid two-phase flow.In this method,aiming to obtain the whole fluid impedance information precisely,a series inductance is introduced to eliminate the unfavorable influence of coupling capacitances.Meanwhile,the phase sensitive demodulation method is used in the signal processing circuit to obtain the real part and the imaginary part of the impedance information,and hence the complete impedance information is obtained.(2)Geometric structure parameters of the radial contactless resistance sensor used in the proposed impedance measurement method are optimized.Simulation and practical experimental results show that the sensitivity of the sensor is optimal when the electrode length is 1.5 times of the pipeline inner diameter and the electrode angle is 120 degrees.(3)A new contactless impedance sensor is developed on the basis of the above simulation and experimental results.To test the performance of the designed sensor,both simulated impedance measurement experiments and practical conductivity measurement experiments are carried out.The experimental results show that the relative errors of the simulated impedance measurement experimental results are within 5%and the relative errors of the practical conductivity measurement experimental results are within 5%as well.The proposed method is effective,and the development of the sensor is successful.(4)The new contactless impedance sensor is used to implement the pattern identification of gas-liquid two-phase flow.With the K-means clustering algorithm,a new method of pattern identification for gas-liquid two-phase flow is proposed.Experiments are carried out respectively in three pipelines with different inner diameters(3.5mm,5.5 mm and 8.2 mm).The experimental results show that the proposed pattern identification method is effective.The experimental results also show that compared with the experimental results of flow pattern identification using only the real part,the imaginary part or the amplitude information,the identification accuracy is improved obviously with the proposed method.The feature vectors of the measured signal are constructed by using the mean values,variances,and the frequency characteristics(extracted by Fourier transform)of the real part,the imaginary part and the amplitude.Flow pattern identification of four typical flow regimes(annular flow,bubble flow,slug flow,and stratified flow)was conducted by K-means clustering algorithm.The accuracy of flow pattern identification is above 88%?97%?90%?90%,respectively.(5)The new contactless impedance sensor is preliminarily applied to the void fraction measurement of gas-liquid two-phase flow,and a new method of gas-liquid two-phase flow void fraction measurement is proposed.The void fraction measurement models are established for four flow regimes,respectively.According to the results of flow pattern identification,different measurement model is selected to calculate the void fraction of gas-liquid two-phase flow.Experiments are carried out respectively in three pipelines with different inner diameters(5.5 mm and 8.2 mm).The experimental results show that the proposed void fraction measurement method is effective.The absolute errors of the experimental results in two pipelines are both within 7%.Compared with the experimental results using only the real part,the imaginary part or the amplitude information,the accuracy of void fraction measurement is improved with the proposed method.In summary,the research results obtained in this work verify that the proposed contactless impedance measurement method is feasible.The developed contactless impedance measurement sensor can obtain the whole impedance information of two-phase flow.The sensor can realize pattern identification and void fraction measurement of gas-liquid two-phase flow successfully.The work of this thesis can provide a useful reference for the parameter measurement of gas-liquid two-phase flow.