Research On Characteristics Of Precessing Vortex Based On Three-axis Acceleration Sensor

The swirlmeter,which is widely used in industry,uses the principle of forced vibration vortex precession to measure flowrate.When pure gas passes through the swirler,the flow rate is calculated according to the precession frequency signal of the vortex.However,when the swirlmeter is used in wet gas measurement,accuracy will be decreased due to the influence of liquid-phase on the vortex signal.In order to study the characteristics of wet gas flowing through the swirlmeter,a complete measurement system was built,in which the traditional piezoelectric probe was replaced by a MEMS three-axis acceleration sensor.In the cases of dry gas,wet gas,and pseudo-slug flow,the three-axis acceleration sensor was used to detect the vortex signal.The main research contents include:Each side of the traditional swirlmeter was connected with a differential pressure transmitter in parallel.The dimensional analysis method was used to dig out the key parameters that affect the frequency signal and the pressure loss signal,such as gasphase Froude number,liquid-to-gas density ratio and Lockhart-Martineli parameter.The experiment was carried out on the wet gas flow rig.By analyzing the relationship between frequency,pressure loss and liquid volume fraction(LVF),a dual-model of frequency and pressure loss was established.The dual-model completed the correction of the gas-phase flow rate and achieved the measurement of ultra-low LVF.When the confidence probability is 95%,the relative error of the gas volume flow rate is 0.797%,and the absolute error of the LVF is 0.028%.In order to extract more abundant vortex signals,the traditional piezoelectric probe in the swirlmeter was replaced by a MEMS three-axis acceleration sensor,and a matching sensor measurement system was designed.This system is composed of the measurement circuit and power supply circuit,the design and packaging of the probe structure,the sampling module of three-axis signals,and the online storage and display interface.The dry gas experiment under normal pressure was carried out based on the threeaxis acceleration sensor measurement system.In the experiment,a sampling frequency of 5KHz was set,and an extended experiment with a sampling frequency of 8KHz was added.On the one hand,after observing the law of the amplitude and frequency parameters of the three-axis acceleration signal,it was shown that there was a linear relationship between the main frequency of the Z-axis signal and the gas-phase flow rate.On the other hand,frequency overlapping and probe resonant were found.The experiment results of dry gas showed that the three-axis acceleration sensor has a high sensitivity with a minimum resolution of 0.001 g.At the same time,the extended experiment showed that the three-axis acceleration sensor has a good reproducibility.Furthermore,based on the three-axis acceleration sensor,the characteristics of wet gas and pseudo-slug flow were studied.In wet gas flow,the amplitude and main frequency of the Z-axis signal showed a non-linear decline trend.Under pseudo-slug flow,the amplitude and frequency characteristics of the vortex signal were relatively complex.From the release to the disappearance of the liquid slug,it was found that the change interval of Y-axis amplitude was the duration of pseudo-slug flow.At the same time,when the pseudo-slug flow came,obvious vortex signals can be detected on the Z-axis.Based on this,the assumption of the combined effect of gas-phase and liquidphase was proposed.In addition,there is an approximately linear rise trend between the total liquid-phase flow rate and the Z-axis frequency.According to the relationship,the estimating formula for the slug volume was given.The results showed that the average absolute error of the estimated value of the liquid slug volume is 0.899 L,and the average relative error is 30.0%.