| Gas-liquid two-phase flow exists widely in the nature and industrial process,its parameter measurement is of great importance for academic research and industrial application.Up to date,the parameter measurement methods of gas-liquid two-phase flow cannot meet the higher and higher measurement requirements,so more research works should be carried out.The parameter measurement methods based on the conductance measurement technique are classic measurement methods and have been widely applied and studied for many decades.These methods have simple structure,good real-time performance and are suitable for industrial environment.Although significant progress has been obtained,there are still two drawbacks of the conventional methods:(1)Most of the methods are on the basis of contact conductance measurement technique and electrodes are directly in contact with the measured fluid,which will lead to the electrode polarization and the electrochemical erosion,and may disturb the fluid flow.(2)In most of the methods,only the real part or the amplitude of the obtained impedance information of gas-liquid two-phase flow is used and the usage of the obtained impedance information(especially the imaginary part of the impedance)is not sufficient.The emergence of the Contactless Conductivity Detection(CCD)technique provides an approach to overcome the problems of contact conductance measurement technique.However,as a developing technique,the conventional CCD technique still does not utilize the impedance information sufficiently.In this dissertation,two new Contactless Impedance Detection(CID)sensors are developed by extending and modifying the conventional CCD sensor.Meanwhile,by combining the new CID sensors and information processing methods,new parameter measurement methods for gas-liquid two-phase flow are proposed to realize the flow pattern identification,the velocity measurement and the void fraction measurement of the gas-liquid two-phase flow.The main innovations and contributions are listed as follows:1.A new Inductance Elimination based Contactless Impedance Detection(IE-CID)sensor is developed.In the IE-CID sensor,a simulated inductor is introduced to overcome the unfavorable influence of coupling capacitances.The analog phase sensitive demodulation(APSD)technique is introduced to obtain the total impedance information(including the real part and the imaginary part)of the measured fluid.The experimental results show that the development of the TE-CID sensor is successful and the impedance measurement accuracy is satisfactory.In the simulation experiments the maximum relative errors of the resistance measurement and the capacitance measurement are 3.86%and 4.85%,respectively.In the conductivity measurement experiments,the maximum relative error of the conductivity measurement is 4.80%.2.A new Conductance Elimination based Contactless Impedance Detection(CE-CID)sensor is developed.In the CE-CID sensor,a capacitance model is introduced to overcome the unfavorable influence of coupling capacitances.The analog phase sensitive demodulation(APSD)technique is introduced to obtain the total impedance information(including the real part and the imaginary part)of the measured fluid.The experimental results show that the development of the CE-CID sensor is successful and the impedance measurement accuracy is satisfactory.In the simulation experiments the maximum relative errors of the resistance measurement and the capacitance measurement are 4.42%and 5.14%,respectively.In the conductivity measurement experiments the maximum relative error of the conductivity measurement is 4.56%.3.Combining the two CID sensors(the IE-CID sensor and the CE-CID sensor)with the Fuzzy C-Means(FCM)algorithm,the IE-CID based flow pattern identification method for gas-liquid two-phase flow and the CE-CID based flow pattern identification method for gas-liquid two-phase flow are proposed.The CID sensors are used to obtain the total impedance information and the FCM algorithm is used to develop flow pattern classifiers.Flow pattern identification experiments are carried out with channels of different inner diameters(2.48mm,3.64mm and 4.52mm).The experimental results show that the proposed methods are effective.For the two new CID sensors,the flow pattern identification accuracies of bubble flow and slug flow are all higher than 96.0%.4.The two new CID sensors(the IE-CID sensor and the CE-CID sensor)are introduced to implement velocity measurement of gas-liquid two-phase flow.The IE-CID based velocity measurement method for gas-liquid two-phase flow and the CE-CID based velocity measurement method for gas-liquid two-phase flow are proposed.Correspondingly,the IE-CID based three-electrode velocity measurement system and the CE-CTD based four-electrode velocity measurement system are developed.With the new methods,the velocity measurement systems are used to obtain the impedance information of the measured gas-liquid two-phase flow.With the principle of cross-correlation velocity measurement two initial velocities of gas-liquid two-phase flow are obtained by real part and imaginary part signals.A velocity measurement model,which is developed by the penalty function method in advance,is adopted to fuse the two initial velocities.Three prototypes of velocity measurement systems with different inner diameters(2.48mm,3.64mm and 4.52mm)are developed to carry out velocity measurement experiments.The experimental results show that the proposed velocity measurement methods are effective.For the two velocity measurement systems,the maximum relative errors of velocity measurement are all less than 4.5%.Meanwhile,the experimental results verify that making full use of the total impedance information is an effective approach to improve the accuracy of bubble/slug velocity measurement.5.Based on the two new CID sensors(the IE-CID sensor and the CE-CID sensor),the IE-CID based void fraction measurement method for gas-liquid two-phase flow and the CE-CID based void fraction measurement method for gas-liquid two-phase flow are proposed.With the new methods,the CID sensor is used to obtain the impedance(real part and imaginary part)information.Two initial void fractions are obtained by two initial void fraction models which are developed based on the real part and imaginary part,respectively.Then the final void fraction is obtained by fusing the two initial void fractions with a final void fraction model.The void fraction models(the two initial void fraction models and the final void fraction model)are developed in advance based on the Levenberg-Marquardt method,by studying the relation between the impedance and the void fraction.Void fraction measurement experiments are carried out with channels of different inner diameters(2.48mm,3.64mm and 4.52mm).The experimental results show that the proposed methods are effective.For the two new CID sensors,the maximum absolute errors of void fraction measurement of bubble flow are all less than 1.0%and the maximum absolute errors of void fraction measurement slug flow are all less than 5.5%.Meanwhile,the experimental results also show that making full use of the total impedance information can improve the measurement performance of bubble/slug void fraction measurement. |
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