Research On Measurement Method Of Gas-liquid Two-phase Annular Flow Based On Multimodal Ultrasonic Technology

Gas-liquid annular flow widely exists in industrial fields such as oil-gas field development and natural gas pipeline transportation.Its online non-separation measurement is significant for reducing production and development costs,optimizing production process technology and improving dynamic monitoring level.Due to the complex flow state and mechanism of gas-liquid flow,it is very difficult to accurately measure the flow rate under the non-separation condition.At present,it is still a research difficulty and hotspot in the multiphase flow field.Therefore,the flow measurement method of gas-liquid annular flow without separation based on multimodal ultrasonic technology is studied in this thesis.The main research contents are as follows:(1)Aiming at the defects of ultrasonic technology in measuring thin liquid film,the ultrasonic echo resonance main frequency method and the ultrasonic reference signal elimination method are proposed.These two ultrasonic methods are compared and verified by using particle image method,conductance probe method and numerical simulation method.The minimum liquid film thickness measured by the two ultrasonic methods are 0.3 mm and 0.01 mm,respectively.Based on this,the experimental data of disturbance wave velocity under five pressure conditions of 0.1 MPa～0.7 MPa are obtained,and the existing four disturbance wave velocity predictive models are analyzed and evaluated.By introducing the influence of system pressure on disturbance wave velocity,the optimized wave velocity model suitable for horizontal gas-liquid flow is established.Compared with the experimental data in this thesis and the existing literature,the average absolute errors of the optimized wave velocity model are 6.179%and 14.979%,respectively,and the relative errors of 95% working conditions is less than ± 15% and that of 94% working conditions is less than ±25%,respectively.(2)The distributed ultrasonic sensor system is designed,and the multi-channel synchronous ultrasonic measurement system is developed.The specific selection and parameter configuration of each module in the self-developed transceiver circuit and data acquisition system are discussed,and the distributed measurement of the circumferential liquid film thickness of the pipe is realized.Besides,the fluctuating characteristics,distribution asymmetry and average film thickness of circumferential liquid film are deeply analyzed.A predictive model of circumferential liquid film thickness suitable for horizontal pipe under medium and high pressure is proposed,and the relative errors of 94% working conditions is within ±25%.(3)The specific parameter setting for simulating the horizontal gas-liquid annular flow based on CFD numerical simulation method is discussed.The correctness of the simulation method is verified by comparing the physical quantities such as liquid film thickness and wave velocity in the simulation results with the experimental values.On this basis,the generation mechanism and dynamic evolution process of entrained droplets in annular flow are revealed,and the generation and deposition characteristics of entrained droplets are studied.Moreover,the droplet entrainment model is determined,and the closure equations such as droplet velocity and gas-liquid interface velocity in two-fluid model are established.(4)A two-fluid model modeling measurement system is established.The circumferential film thickness and pressure drop are obtained using the aforementioned distributed ultrasonic thickness measurement technology and differential pressure transmitter.Combined with the closure equation of disturbance wave velocity,droplet entrainment rate,droplet velocity and gas-liquid interface velocity determined by CFD numerical simulation method,the closure equation of gas-liquid interface friction factor is established.Thus,a new two-fluid model suitable for horizontal pipe under medium and high pressure is constructed.Then the flow rate measurement system is designed.Under the conditions of atmospheric pressure and gas superficial velocity with 10m/s～20 m/s and liquid volume fraction with 0.4%～5%,the gas and liquid flow rate are obtained through distributed ultrasonic thickness measurement technology and velocity measurement technology of gas ultrasonic flow sensor combining with the new twofluid model.The relative errors are within ±10% and ±15%,respectively.(5)The numerical simulation method suitable for air-droplet two-phase flow is studied.Based on the simulation,the applicability of the existing ultrasonic attenuation theoretical model in air-droplet two-phase flow is compared and analyzed,and the MCBL ultrasonic attenuation theoretical model suitable for the whole wavelength range is established.The MCBL model and hybrid particle swarm algorithm are used to inverse the droplet size and volume fraction in simulation and static experiments,and the relative errors are within ±15%.The problems existing in static experiments and real flow experiments are summarized and analyzed.