The Study On Mechanism And Optimization Control Of Metering Process For Volatile Liquid

The high saturated vapor pressure and low viscosity characteristics of gasoline and other easily vaporized medium make the filling process extremely volatile and vaporizable,which results in leakage and cavitation,leads to pressure fluctuations in the measurement system,thereby reduces the stability of the pipeline flow and causes serious measurement accuracy influences.In this paper,based on the deep understanding of the physical characteristics of the easily vaporized medium and the above problems,the mechanism of the metering process of the piston-type positive displacement flowmeter and the ultrasonic flowmeter,which are commonly used in the vaporization media measurement system,respectively,is studied in depth and the corresponding optimization control scheme.The main contents are summarized as follows:First of all,taking the reciprocating piston positive displacement flowmeter as the research object,which is commonly used in the measurement system of easy vaporized medium,the measurement error characteristics and the pressure loss characteristics are studied by the combination of theory and experiment.Subsequently,the model of the piston ring-cylinder liner eccentric annular leakage is established,and the main factors affecting the internal leakage are theoretically investigated.Then,in order to optimize the structure of the internal leakage gap,an optimization method of ring-shaped pressure equalization groove on the piston ring is proposed.For the optimization of the internal leakage gap value,the internal leakage lubrication model is established based on hydrodynamic lubrication theory.According to the numerical calculation results,the design values of theoretical clearance when the metering medium is gasoline and diesel are given respectively.Secondly,based on the ultrasonic measurement technology of time difference method,the ultrasonic measurement scheme of three U-shaped measuring units in series is designed for the case that the inner diameter of the easy-to-evaporate medium measuring system is too small to install multiple measuring channels on the same section.Moreover,based on self-learning weighted least-squares multisensor data fusion method of calculating the cumulative flow,the flow calculation formula of the three-channel ultrasonic flowmeter is derived.Then,the flow characteristics and secondary flow of the flowmeter pipeline are analyzed by means of numerical simulation.After that,the ultrasonic flowmeter measurement testing platform is set up,and the measurement error characteristics and reliability are studied respectively.Then,aiming at the problem of serious cavitation caused by the overfilling of the flow and the decrease of the pumping efficiency when the filling flow is too small,based on the principle of a flow control valve and the technology of variable frequency filling,a dynamic feedback control scheme of flow rate range is proposed.Finally,based on the sliding discrete Fourier transform(DFT),a high-precision ultrasonic propagation time estimation method is proposed,which can obtain high estimation accuracy of propagation time difference with a lower sampling frequency.It can not only improve ultrasonic measurement accuracy,but also reduce the amount of computation to process back-end signal.