Flow Characteristics And Measurement In Wet Gas By Using Vortex Flowmeter Coupled With Conductance Ring Sensor

Wet gas two-phase flow widely exist in natural gas,steam boilers,nuclear reactors,aerospace and other engineering applications,among which annular mist flow is the most common two-phase flow pattern.Vortex flowmeters are widely used in the flowrate metering of wet gas flow.However,the presence of liquid affects output signal and can result in the positive deviation of gas flow rate,which affects the accuracy of two-phase measurement.Online accurate measurement of gas and liquid flow rates is beneficial to improve economic benefits.To improve the measuring accuracy of vortex flowmeters in annular mist flow,the analysis of experimental measurement technology and related prediction models is carried out.The research is carried out on the meter overreading and vortex street stability.The main research contents and innovative results are listed as follows:1.Design a liquid film flow parameter measurement system based on the conductance ring.On the basis of the existing conductance ring size,COMSOL finite element simulation is used to optimize the size of the upstream and downstream conductance ring sensors,and the corresponding software and hardware in the measurement system is designed.Aiming at the problem that it is difficult to directly calibrate the thickness of the liquid film below 2 mm for the conductance ring,an equivalent calibration scheme is proposed,and the feasibility of equivalent calibration is proved by simulation and experiment.Finally,the equivalent calibration experiment was carried out,and the output characteristic curve of the conductance ring sensor in the range of 0.1-1 mm was obtained.The measurement error of the sensor is within±3%,which lays the foundation for the accurate measurement of liquid film thickness,disturbance wave velocity and frequency in annular mist flow.2.Measure and analyze the changes of the liquid film flow parameters in the annular mist flow and conduct theoretical research and modeling.According to the experimental conditions such as gas-liquid flow rates and pressure in annular mist flow,the corresponding sampling parameters are determined,and the liquid film flow data under different working conditions are measured.The change trend of the liquid film flow is analyzed using the measured experimental data.By summarizing the past classic empirical formulas of liquid film thickness and disturbance wave velocity,combined with the dimensionless gas and liquid Weber numbers,prediction models of liquid film flow parameters are obtained.The experimental results show that the percentage errors of the prediction results of the liquid film thickness and the disturbance wave velocity are both within ±5%.3.Analyze the overreading characteristics and stability of the vortex street in the annular mist flow and establish the overreading model.The vortex street overreading signal under different conditions is measured by the annular flow loop experimental device,combined with the measured liquid film fluctuation frequency,the quality factor and Strouhal are used as a medium to analyze the correlation between the vortex street signal stability and the liquid film fluctuation.At the same time,by studying the changes of the overreading coefficient under different flow conditions,a mathematical model between the overreading coefficient and the Weber numbers is obtained.The prediction accuracy of the model is within ±1%,which establishes a foundation for the subsequent exploration of the relationship between the vortex signal and the liquid film signal.4.Two prediction models of gas and liquid flow rates in annular mist flow are proposed: a vortex street overreading compensation model based on Newton iterative algorithm and liquid film flow parameters.Two different solutions are used and corresponding algorithms are designed to predict the flow rates of gas and liquid in the annular mist flow,and the advantages and disadvantages of the two algorithms are analyzed.The gas flow rate percentage error PE predicted by the two methods is ±1.5%,and the maximum full-scale percentage error FSPE predicted by the liquid flow rate is±5%.By combining the vortex flowmeter and the liquid film flow parameter measurement system,it provides an economical and accurate online measurement program for the gas and liquid flow rates measurement of the annular mist flow.