Gas-liquid Flow Behavior And Separation Mechanism For The Upper Cylinder In Gas-liquid Cylindrical Cyclone(GLCC)

The Gas-liquid Cylindrical Cyclone?GLCC?,an extremely lightweight gas-liquid separation device,has a promising application prospect in the underwater production system of offshore oil and gas.However,its application as a complete separator is still immature yet due to the underperformed separation efficiency.One reason for this is the phenomenon of Liquid Carry-over?LCO?,which refers to the liquid phase being carried away by gas from the outlet.To solve the problem,the recognition of separation process and mechanism is an inevitable and crucial point.In this thesis,the flow behaviors of liquid film phase and droplet phase in the upper cylinder of GLCC are studied in detail by means of numerical simulation,experimental verification and theoretical analysis.The results and conclusions are as follows:?1?The simulating methods of gas-liquid flow in GLCC are improved.Optimization for the turbulence model,multiphase model,drag force model of gas-liquid flow field is realized,together with a user-defined boundary which has taken the inlet non-uniform profile of gas-liquid two phase flow into consideration.Then the liquid film and droplets are simulated respectively.For the liquid film,the Eulerian Wall Film?EWF?model is introduced to obtain the film`s flow characteristics on the cylinder wall,which is coupled with the Eulerian-Eulerian approach and the Population Balance Model?PBM?.For the droplets,the effects of turbulent diffusion and wall film are included into the Discrete Phase Model?DPM?to track the original droplets,and then the TAB breakup model and O`Rourke coalescence model are added to calculate the secondary droplets.By these above-mentioned improvements,a comprehensive numerical simulation method is established for the GLCC`s gas-liquid two phase flow.Its simulated pressure drop,film thickness and droplets size distribution are all in good agreement with our experimental results.?2?This thesis explores the flow behavior of liquid containing both film phase and droplet phase in the GLCC upper cylinder.According to the liquid holdup law and the spatial distribution of centrifugal force and axial drag force under different operating conditions,it is found that the percent-LCO shows a positively linear relationship with the entrainment rate F_E,a decreasing-then-increasing relationship with the Somofield number K?the turning point K 57.7?,and an opposite relationship with the critical diameter separated factor S_p0.?3?The change law of film thickness,axial velocity and tangential velocity with the gas-liquid throughput are analyzed for the Upper Swirling Liquid Film?USLF?.Typical flow features of USLF are refined and summarized.The liquid film thickness and film tangential velocity gradually decay along the axis,while the film axial velocity decays along the axis with vibration and fluctuation.These variables are more sensitive to the gas flowrates than to the liquid flowrates.Moreover,it is observed that the axial velocity of liquid film may reverse from negative to positive.Accordingly,the flow regimes of USLF can be recgonized as swirling flow,churn flow and annular flow.When the film axial velocity keeps negative,the USLF can be identified as swirling flow.When the axial velocity reverses from negative to positive,the USLF can be identified as churn flow.And when the axial velocity keeps positive all the way,it can be identified as annular flow.?4?The trajectory tracking of droplets is able to depict the size distribution of escaped droplets?1?10?m?.Meanwhile,the influences of secondary droplets?breakup,coalescence and splashing?on the separation efficiency of GLCC are evaluated by particle statistics.It shows that these influences can generally be ignored because they usually occur when liquid droplets are over 30?50?m.?5?A judgment criterion of USLF flow pattern is established based on the flooding theory.The transitions of flow patterns from swirling flow to churn flow or from churn flow to annular flow can be identified through analyses of force balance and upward flow rate.By verification,this criterion model matches the experimental phenomena very well for the air-water,air-glycerin and air-T55 systems.?6?A feasible pattern-classified-based calculation model for the percent-LCO is presented.In view of the liquid mass conservation in the cylinder space,a quantitative treatment method which regards the percent-LCO as a sum of the droplets escaping rate?percent-LDCO?and the film overflow rate?percent-LFCO?is proposed.The percent-LFCO are calculated respectively according to the flim flow characteristics under different USLF flow patterns.And the percent-LDCO are calculated correspondingly for different size distribution of inlet droplets.For the swirling flow,its percent-LFCO is zero.For the annular flow,its percent-LCO can be calculated as a stable film overflow rate by using the separated fluid model.For the churn flow,the percent-LFCO can be obtained by iterating of a multi-standing waves model,which is developed from the standing wave theory.This mothed corrects the shortcomings of previous methods which did not consider the liquid film overflow.The calculated results are in agreement with the experimental results.It can provide guidance for the design and application of GLCC.