Simulation And Experimental Research On Wet Gas Measurement Characteristics Of Venturi And Crescent Orifice

As a special gas-liquid two-phase flow,wet gas generally exists in the production process of petrochemical industry and natural gas industry.Due to its complexity,the precise measurement of wet gas is still a topic worthy of research.The flow characteristics of wet gas flowing through long throat venturi and crescent orifice were simulated by CFD.At the same time,the experimental models were established for comparative study.The main research contents include:(1)Simulation study on wet gas flow field of long throat venturi.Based on the VOF multiphase flow model and the RNG k-ε turbulence model,the flow law and differential pressure characteristics of the stratified flow through the long throat venturi were simulated.As the fluid flows through the venturi throat and expansion section,the change of the flow state is well simulated,and the entrainment phenomenon of the liquid film is observed.When the fluid flows through the throat of the venturi,the true flow velocity of the gas and liquid phases increase,the velocity slip between the gas and liquid phases increases,and the velocity slip ratio decreases.Within the range of 5% of the liquid content,there is a relatively monotonous relationship between the K value of the long throat venturi and the liquid content.(2)Simulation study on wet gas flow field of crescent orifice.In order to solve the problem of low liquid content measured by traditional axisymmetric throttling flowmeter,a non axisymmetric crescent orifice with bottom flow channel was proposed.The flow characteristics of stratified flow through the crescent orifice were simulated with the use of the VOF model.The simulation results show that after the fluid flows through the orifice,the pressure recovers at about 6D(0.3m)downstream,and the flow tends to be stable.With the increase of gas velocity,the vortex increases,the flow becomes more complex,and the vortex length decreases.The void fraction is higher than that in front of the orifice plate,and the liquid level decreases.In the range of liquid content of 15%,there is a good monotonous relationship between the K value and the liquid content,which can effectively identify the liquid content.(3)Comparison of wet gas measurement characteristics between long throat venturi and crescent orifice.The experiments of two kinds of flow meters were carried out on the adjustable pressure medium pressure wet gas experimental facility of Tianjin University.The experimental results show that based on the VOF model,the differential pressure of the flowmeter is better predicted.When the liquid content is greater than 5%,the inflection point exists in the relationship curve between venturi K value and liquid content.But,the measuring range of crescent orifice plate is wider,and there is no inflection point within15% liquid content.For long throat venturi,when the liquid content is less than 5%,the relative error of gas flow rates is within ± 3%,and there are 99.2% operating points where the full-scale error of liquid flow rates is within ± 3%.For crescent orifice,within the range of liquid content of 0～15%,the relative error of gas flow rates at 97%operating points is within ± 5%,and the full-scale error of liquid flow rates at 99%operating points is within ± 5%.