| Gas-liquid two-phase flow widely exists in industrial process.Its effective parameter measurement is of great importance but is still a problem that has not been solved well.The gas-liquid two-phase flow parameter measurement method based on conductivity detection has received great attentions from researchers because of its simple structure and quick real-time response.However,the present electrical measurement technique based on conductivity detection still has two disadvantages.In terms of the measurement mechanism,it is a contact technique.The electrodes of the sensors are directly in contact with the fluid which will cause the polarization effect and the electrochemical reaction.In terms of the measurement information,the purpose of the present conductivity detection method is merely to obtain the equivalent conductance information.For the complicated gas-liquid two-phase flow,obtaining the complete impedance(the real part,the imaginary part and the amplitude)which contains more flow characteristics will be more beneficial to the measurement of the gas-liquid two-phase flow parameters.According to these two disadvantages,in this dissertation,the shortcomings of the present Capacitively Coupled Contactless Conductivity Detection(C4D)are overcome,a new contactless impeda1ce sensor is developed and the complete impedance information is used to implement the measurement of gas-liquid two-phase flow parameters.The main innovation points and contributtions are listed as follows:1.To overcome the drawback of the industrial C4D sensor(the non-monotonic input-output characteristic)developed in our previous work,a new contactless conductivity detection method based on two-inductor serious resonance principle is proposed and a new industrial C4D sensor with two-inductor structure is developed.In this new method,two practical inductors are connected to the excitation electrode and the detection electrode,respectively.By the two-inductor stricture,the unfavorable influence of the coupling capacitances on the conductivity mearuement and the drawback of our previous industrial C4D sensor are overcome.The experimental results show that the proposed new contactless conductivity detection method is effective and the developed new industrial C4D sensor with two-inductor structure is successful.In four pipes(the inner diameters are 1.8 mm,3.3 mm,5.0 mm and 7.6 mm),the maximum relative errors of conductivity detection are less than 4%.2.According to the drawbacks of the practical inductor(the limited adjustable range of the inductance,the difficulty to develop a large-valued practical inductor and the large size problem),the simulated inductor technique is introduced and a new contactless conductivity detection method based on simulated inductor series resonance principle is proposed.A symmetrical floating simulated inductor and a new C4D sensor with a symmetrical floating simulated inductor are developed.The research results indicate that the designs of the symmetrical floating simulated inductor and the new C4D sensor are successful.The equivalent inductance of the symmetrical floating simulated inductor is adjustable and can be adjusted to a relatively large value.The performance and the conductivity detection accuracies of the new C4D sensor are satisfactory.In three pipes(the inner diameters are 3.0 mm,4.6 mm and 6.4 mm),the maximum relative errors of the conductivity detection are less than 5%.3.Considering the structure complexity and the running stability of the symmetrical floating simulated inductor,two kinds of new C4D sensor with a grounded simulated inductor are developed.One is the new C4D sensor A,which implements the conductivity measurement by the current-to-voltage conversion.The other is the new C4D sensor B,which implements the conductivity Leasurement by the differential voltage measurement.In three pipes(the inner diameters are 3.0 mm,4.6 mm and 6.4 mm),conductivity detection experiments are carried out with C4D sensor A and C4D sensor B.The experimental results indicate that the designs of the grounded simulated inductor and the new C4D sensors are successful.Compared with the symmetrical floating simulated inductor,the grounded simulated inductor has the merits of simple structure and good running stability.The conductivity detection accuracies of the new C4D sensors are satisfactory(In three pipes,the maximum relative errors of the conductivity detection with the new C4D sensor A and the new C4D sensor B are 4.5%and 5.0%,respectively.).The measurement performance of the C4D sensor A is better than that of the C4D sensor B.4.Combining the grounded simulated inductor impedance elimination technique and the Digital Phase Sensitive Demodulation(DPSD)technique,a new contaceless impedance measurement method is proposed and a new contactless impedance sensor is developed.In this new method,the negative influences of the coupling capacitances on the impedance measurement can be eliminated based on the impedance elimination principle.The DPSD technique is introduced to obtain the complete impedance(the real part,the imaginary part and the amplitude)of the gas-liquid two-phase flow.The simulation measurement experiments and the real fluid measurement experiments results indicate that the new method is effective and the contactless impedance sensor is successful.In the real resistance measurement and the real capacitance mearuement experiments,the maximum relative errors are 3.7%and 2.4%,respectively.In the resistance-capacitance combination measurement experiments,the maximum relative errors of resistance and capacitance measurement are 2.1%and 5.1%,respectively.In the conductivity measurmen of KC1 solution and the permittivity measurement of organic solvents experiments,the maximum relative errors are 3.7%and 5.8%,respectively.5.Combining the new contactless impedance sensor with the Wavelet analysis method and the k-means clustering algorithm,a new pattern identification method based on contactless impedance measurement for gas-liquid two-phase flow is proposed.In this new method,the Wavelet analysis method is used to exextract the frequency features of each part of the impedance signal to obtain the feature vector by combining the statistical features.The k-means clustering algorithm which regards the Mahalanobis distance as the distance parameter is applied to classify the flow patterns.The experimental results in three pipes with the inner diameters of 3.0 mm,4.0 mm and 7.0 mm show that the proposed pattern identification method is effective.The minmun identification accuracies of bubble flow and slug flow by using the real part,the imaginary part,the amplitude and the complete impedance information are 91.1%and 90.9,90.2%and 87.9,92.7%and 87.0%,and 91.1%and 93.5%,respectively.The identification results by using the complete impedance information is slightly better than the identification results by using only the real part,the imaginary part or the amplitude.6.A new void fraction measurement method based on contactless impedance measurement for gas-liquid two-phase flow is proposed.In this method,each part of the gas-liquid two-phase flow impedance signals have been fully used.The Least Squares method is introduced to develop the void fraction measurement models for different flow patterns in advance.According to the flow pattern classification results,the corresponding void fraction measurement models will be used to implement the void fraction measurement in the practical measurement process.In three pipes with the inner diameters of 3.0 mm,4.0 mm and 7.0 mm,respectively,the void fraction measurement of bubble flow and slug flow are carried out.The experimental results verify the feasibility and effectiveness of the proposed new method and it is helpful to improve the accuracy of the void fraction measurement by fully using the complete impedance(the real part,the imaginary part and the amplitude)of the gas-liquid two-phase flow. |
PDF Full Text Request