Research On Two Measurement Methods Of Liquid Volume Fraction For Wet Gas Based On Simulation

Wet-gas is widely found in petroleum,chemical industry,metallurgy industries.As one of the important parameters of gas-liquid two-phase flow,the volume fraction of liquid can not only directly affect the measurement accuracy of flow rate,but also has important significance for industrial production and scientific research.In this thesis,the combination of computational fluid dynamics numerical simulation and real-time experiment is used to study the method of measuring the volume fraction of liquid phase.The main contents include the following aspects:(1)Optimization of Venturi Expansion Section and Measurement of liquid volume fractionThe theoretical analysis is made on the accelerating pressure drop and the frictional pressure drop of the venturi tube based on the suppose that the gas-liquid two-phase is approximation regarded as an mist flow,and find out the main factors that affect the pressure drop change.Based on the combination of DPM model and EWF,a long-throat venturi with a diameter of 50 mm and a throttling ratio of 0.55 was numerically simulated under temperature of 308.15 K and pressure of 4MPa.Four structures were designed based on the expansion angle and the shape of the expanding section.Just to find out the optimum structure which is suitable for wet-gas flow and can improve the ability of linear identification between venturi differential pressure ratio K and liquid volume fraction LVF.It is found that ellipse-straight expansion segment venturi is the optimum structure.Finally,it is further verified by the experiment under pressure of 0.4MPa and 0.8MPa that the ellipse-straight expansion segment venturi ensuring the stability of wet-gas flow and broadened the linearity between differential pressure ratio K and LVF from original LVF 1.5% to LVF 5%.Breaking the limit of long throat venturi measured in the high ratio of liquid phase.(2)Method for liquid volume fraction measurement with capacitor based on Integrated hydrocyclone technologyStarting from the capacitor structure,an integrated hydrocyclone device is designed.The device achieves the gas concentration in the central region and the phase distribution of the liquid phase along the pipe wall through the swirling vanes.Using the mixed turbulence in the RNG k-? turbulence model provided by Fluent 14.0 software,two-phase high-intensity rotating flow inside the measuring section was solved.Combined with the Eulerian multiphase flow model,the velocity and volume fraction of gas-liquid two-phase flow at 0.6,0.9 and 1.2 MPa were analyzed and compared respectively,and the capacitor which was uniquely related to the volume fraction of liquid phase was constructed.That is,a metal cylinder with radius of 50 mm and length of 300 mm.A metal inner electrode with diameter of 32 mm and length of 216 mm is inserted at the center of the metal cylinder,and 4 turns of insulating swirler vanes are provided between the inner and outer electrodes.Based on that,the capacitance values corresponding to different liquid levels were obtained by 3D finite element Comsol simulation.A prototype of capacitance-water measurement principle was developed based on the above parameters,the same experiment was carried out on the medium-pressure moisture experimental device of Tianjin University Flow Laboratory.The results show that the simulation and experimental comparison are more ideal when the gas flow velocity is more than 5m / s,when the flow velocity is lower than 5m / s the deviations are large.However,the simulation was used to confirm the limitation of the prototype,it is that liquid phase distribution will cause short circuit of capacitor in the case of low flow rate and high liquid content.So the study lays the foundation for the further research of the subsequent water analyzer.