Study On Flow Characteristics Of Two-phase Flow Through Horizontal Pipe With Sudden Expansion

Sudden expansion structure is widely used in energy power,chemical industry,environmental protection and other fields.With the development of most onshore oil fields in China has entered the middle and late stages of development,water injection development makes the surface gathering and transportation system and long-distance pipeline network in the oil-water two-phase flow widespread.Therefore,it is very important to study the flow characteristics of two-phase flow in the sudden expansion pipe for the reasonable selection of oil transportation mode and pumping efficiency.Based on the basic principles of fluid mechanics and the basic governing equations of fluid motion,combined with the relevant knowledge of oil-water two-phase flow,the CFD software FLUENT is used to simulate the structural parameters(sudden expansion ratio,thin tube length,thick tube length)and physical parameters(water content,viscosity,Reynolds number)of oil-water two-phase flow through the sudden expansion section.Combined with phase distribution cloud map,pressure distribution map,flow chart and other intuitive means,it is found that the sudden change of boundary shape leads to flow separation and reattachment after sudden expansion cross section,and then leads to vortex.different sudden expansion ratio has a great influence on the horizontal sudden expansion flow.When the sudden expansion ratio is less than 2,the reflux at the upper and lower shoulder of the sudden expansion is basically symmetrical and the flow is relatively stable,However,when the sudden expansion ratio is greater than 2.5,the flow at the upper and lower shoulders of the sudden expansion appears obvious asymmetry,and the slope of pressure drop corresponding to different sudden expansion ratio is quite different.The length of the thin tube and the thick pipe at the sudden expansion section have no effect on the flow,but have little effect on the friction coefficient,when the water content is low,the flow pattern of the two-phase flow is "oil-in-water",and the flow resistance is larger and the pressure loss is larger.When the water cut increases to 0.5,the two-phase flow pattern becomes "oil in water",and the flow resistance is smallerand the pressure loss is smaller.With the continuous increase of crude oil viscosity,the length of the water phase wetting wall decreases,the oil phase wetting wall length increases,and the pressure loss increases gradually.With the continuous increase of Reynolds number,the reflux vortex structure of upper and lower shoulders increases continuously after sudden expansion,which increases the flow loss and pressure loss.The research results in this paper are very important for understanding the flow characteristics of sudden-expanding two-phase flow in crude oil gathering pipeline network,reducing pipeline corrosion,optimizing pipeline structure,and reducing energy loss,so as to ensure safe production and optimize process.