Research On Parameter Measurement Of Small-Pipeline Gas-liquid Two-phase Flow Based On The Three-electrode Contactless Electrical Impedance Sensor

Gas-liquid two-phase flow widely exists in nature and industry,and its parameter detection has important scientific research and practical application value.With the miniaturization of industrial equipment,the small-pipe two-phase gas-liquid flow system is one of the hotspots in the field of current two-phase flow and has drawn more and more attention from researchers.However,the research on the parameter detection technique of small-pipe gas-liquid two-phase flow is still in the developing stage and needs further study.Therefore,the research on the parameter detection of small-pipe gas-liquid two-phase flow has important scientific value and broad application prospect.In this thesis,the flow pattern identification and flow velocity measurement of gas-liquid two-phase flow in small horizontal pipelines are studied by using electrical detection method.The main contents and innovation of this dissertation are as follows:1).Based on the capacitively coupled contactless detection(C4D)and phase sensitive demodulation techniques,a three-electrode capacitively coupled contactless electrical impedance sensor was proposed to obtain the complete electrical impedance of gas-liquid two-phase flow information.Meanwhile,in order to eliminate the influence of the coupling capacitance on the measurement,a series inductance is introduced to eliminate the capacitive reactance generated by the coupling capacitance in the inductance of the series inductance and improve the signal-to-noise ratio.2).Based on the three-electrode capacitively coupled contactless electrical impedance sensor,a gas-liquid two-phase flow parameter measurement system for small pipelines is designed and built.The experimental study has been carried out in small pipelines with different inner diameters of 2.50 mm,3.64 mm and 4.72 mm,respectively,to realize the identification of four typical flow patterns of bubbly flow,slug flow,stratified flow and annular flow in gas-liquid two-phase flow and the velocity measurement of two flow patterns of bubble flow and slug flow,respectively.3).A gas-liquid two-phase flow pattern identification method is proposed.In the method,the real part information and the imaginary part information of the impedance measurement signal are obtained by the three-electrode capacitively coupled contactless electrical impedance sensor.Then,the real part of signals and the imaginary part of signals are decomposed into 4 sub-bands by wavelet packet decomposition technique,and energy distributions of different frequency ranges were calculated.By combining the mean and variance of the real part and the imaginary part of the signal,the feature vectors are constructed.Finally,K-means clustering algorithm is used to establish flow identification model.The experimental results show that the proposed flow pattern identification method is effective,and the flow pattern recognition accuracy can reach 90.7%.The experimental results also show that the accuracy of the flow pattern identification is significantly improved by using the complete electrical impedance information compared with using only one of amplitude information,real part information or imaginary part information.4).A gas-liquid two-phase flow(bubble flow/slug flow)velocity measurement method is proposed.In this method,the upstream signal and the downstream signal are obtained by the three-electrode capacitively coupled contactless electrical impedance sensor.The upstream and downstream signals are cross-correlated to obtain the initial flow velocity.Then,according to the proposed flow identification model,the calibration coefficient is obtained.With the calibration coefficient,flow velocity can be obtained.The experimental results show that the proposed flow velocity measurement technique is effective,and the relative error of flow velocity measurement is less than 6%.