Research On The Characteristics Of Axial Swirling Flow Field And Behavior Of Droplet

In the process of mixed transportation of petroleum resources,the water phase in the flow field which influenced by internal or external factors will precipitate and accumulate at the bottom of the pipeline and form a liquid film,which will have a serious impact on the pipeline life and oil quality.Axial swirling technique is one of oil-gas-water pipeline separation method.It generates swirling flow field by means of diversion structure and replaces gravity settlement with swirling separation,which has an advantages of high efficiency and small occupation of land.In this paper,the technology is introduced into the treatment of liquid film in long-distance pipeline,and a convex helical diversion structure is proposed.In order to explore its working performance and flow field characteristics,a series of research work is carried out by combining experimental research with numerical simulation.Firstly,an oil-water two-phase flow circulation system is built.The inner diameter of the pipeline is 50 mm,the slope is 10%.White oil is used in oil phase and domestic water is used in water phase.And conduct the test of using transportation oil phase carrying water phase and flow field characteristic in the pipeline with convex helical diversion structure.Secondly,Reynolds stress model(RSM)?Volume of fluid(VOF)?velocity inlet and pressure outlet boundary conditions and Semi-implicit method for pressure linked equation(SIMPLE)are selected to solve the unsteady state.The oil-water two-phase settings are consistent with the experiment.The oil-water phase transport and flow field characteristics under different flow conditions are studied.Finally,the discrete phase is simulated,and the droplet motion is simulated by Discrete phase model(DPM).The droplet breakup and coalescence behavior is simulated by TAB model and O'rouke's model.The droplet motion and characteristic particle size change under different flow rates are studied.Results: The water phase will be rolled up and carried in the swirling flow field,and the carrying time is approximately exponential with the flow velocity.After the swirling flow field is generated,it develops to the strongest in the downstream 2 times pipe diameter,and can maintain 24 times pipe diameter distance.The larger the flow velocity,the stronger the swirling flow field is.The maximum of velocity amplitude is located in the center of the diversion zone,which is more than three times of the inlet velocity.The axial and tangential velocities are fan-shaped in the cross section of the diversion zone,and the pressure is inverted bell-shaped in the longitudinal section of the diversion zone.For discrete phase droplets,the collision and coalescence of droplets are dominant before the swirling flow field is stable,and then the breakup is dominant.When leaving the diversion zone,the cliff-breaking decreases occurred on the minimum particle diameter.