Study On Gas-Liquid Two-Phase Flow Characteristics Inside Blind-Tee Pipes

In offshore oil and gas production systems,multiphase flow transportation technology is often used to simplify the equipment structure of the production platform and reduce operating costs.In order to improve the mixing condition of oil and gas products in mixed transport system,blind-tee pipes are widely used as mixing device upstream of multiphase flowmeter in subsea pipelines.However,the selection of the installation position of multiphase flowmeter downstream of the blind-tee and the design of the blind-tee structure still rely on experience,without specific theoretical guidance.For deeply understand the flow characteristics and mixing mechanism of gas-liquid two-phase flow in blind-tee pipes and determine the optimal installation position of multiphase flowmeter downstream of the blind-tee pipe,a series of numerical and experimental studies were carried out on the gas-liquid two-phase flow in blindtee pipes.Firstly,the population balance model coupled with the Eulerian-Eulerian two-fluid model were used to simulate the gas-liquid two-phase flow in traditional elbow pipes and typical blindtee pipes,and the accuracy and reliability of the numerical method were verified by comparing with the experimental and simulation data in the existing literature.On this basis,the flow characteristics of gas-liquid two-phase fluid flowing through the traditional elbow and the typical blind-tee structure were analyzed in detail,in order to explore the mixing mechanism of multiphase flow in different turning structures and its influence on the downstream flow characteristics.Then,the change of the flow condition at the entrance of the blind-tee,the length of the blind-tee and the flow direction were studied,to explore the change rule of the fluid flow in the downstream of the blind-tee pipe and the main factors affecting the mixing effect.Finally,based on the existing multiphase flow experiment platform,the pipeline needed for the multiphase flow experiment in different turning structures is reformed,and the experimental results are combined with the simulation results for the overall analysis.The results of this thesis show that the uniformity downstream of the blind-tee is greater than that of the elbow.The uniformity value of the blind-tee pipe is 50.89% higher than that of the elbow pipe where the uniformity change is relatively stable.The uniformity of fluid distribution downstream of the blind-tee increases first and then decreases.The increasing of the length of the blind end has little effect on the uniformity of fluid distribution downstream of the blind-tee.The change of flow direction has a great influence on the distribution of multiphase fluid flow in the blind-tee pipe.In the case of horizontal to horizontal and horizontal to vertical upward flow,most of the gas phase will directly flow into the downstream.In the case of horizontal to vertical downward,the gas-liquid two-phase fluid is divided into two parts.One-part flows directly into the downstream of the blind-tee pipe through the turning structure,and the other part flows into the blind end of the blind-tee to form a flow circulation.In conclusion,the blind-tee structure has a better mixing effect on the flow of multiphase fluid than the traditional elbow structure.The distribution of multiphase flow with higher uniformity can always be obtained at 8 times pipe diameter downstream of the blind-tee.When the length of the blind tee is less than 2 times pipe diameter,the flow mixing effect can be sufficient for the downstream fluid.The research results of this paper help deepen the understanding of the mixing mechanism of the fluid flow in the blind-tee pipe,and provide theoretical guidance for the design of pipelines in offshore oil and gas production systems,as well as the installation of the flowmeter in the multiphase flow measurement system.