| Gas-liquid two-phase flow is widely involved in nature and industrial production,and the measurement of its parameters has great scientific research value and industrial application significance.Flow pattern is a very important parameter in gas-liquid two-phase flow,which has a significant impact on gas-liquid two-phase flow,so the identification of flow pattern is an important element in the field of gas-liquid two-phase flow research.The gas-liquid two-phase flow parameter detection method based on equivalent conductance detection has the advantages of good robustness,low cost and fast response,and is a common method for gas-liquid two-phase flow parameter detection.However,most of the methods are contact detection methods,in which the direct contact between the detection electrode and the measured fluid will affect the normal flow of the fluid and even cause problems such as chemical corrosion of the electrode;and the conductivity detection method aims to obtain the equivalent conductivity signal of the fluid,but for gas-liquid two-phase fluids,obtaining electrical impedance information containing more flow characteristics will be more beneficial to the detection of gas-liquid two-phase flow patterns.In the equivalent conductivity detection,the method based on Capacitively Coupled Contactless Conductivity Detection(C~4D)can overcome the above problems,but the C~4D technique currently has a small application range and is affected by interference signals during detection.In view of the above problems,this thesis improves the problems of existing C~4D technology,develops a composite shielded C~4D sensor with double inductance structure,and tests the performance of this sensor,and designs a flow pattern detection system based on this C~4D sensor,and finally uses this measurement system to realize the flow pattern recognition of the two-phase gas-liquid flow segment plug flow and bubbly flow.The main work of this thesis includes:1)The current research status of C~4D sensors was investigated and sorted out,and the problems of external signal interference,internal signal interference,and the equivalent capacitive impact of sensors in traditional C~4D sensors were improved by external shielding design,internal shielding design,and series inductor structure design,respectively.The subsequent detection circuit was also designed and built.Based on this,a composite shielded C~4D sensor is developed and its shielding performance is experimentally verified.2)The results show that the input and output(input is the measured conductance value and output is the output voltage signal)characteristics of the C~4D sensor with single inductor structure are nonlinear,while the input and output characteristics of the C~4D sensor with dual inductor structure are linear.It can be seen that the single inductor composite shielded C~4D sensor is not suitable for the detection of flow field parameters,while the dual inductor composite shielded C~4D sensor is suitable for the detection of flow field parameters.The C~4D sensor with dual inductance structure was further tested and analyzed,and the results showed that the developed composite shielded C~4D sensor with dual inductance structure is suitable for low conductivity conditions,and its accuracy of conductivity measurement is higher than 96%.3)Using the developed sensor,the flow pattern identification experiments of gas-liquid two-phase flow under different working conditions were carried out in combination with the designed gas-liquid two-phase flow pattern measurement system.Based on the differences in the time and frequency domains of the equivalent electrical impedance signals of the segment plug and bubble flows obtained by the double inductance shielded C~4D sensor,the electrical impedance signals are extracted;the correspondence between the electrical impedance signals and the segment plug and bubble flows is established by feature classification;the k-mean clustering method is used to realize the flow pattern identification of the segment plug and bubble flows. |
