Study On Gas-liquid Two-phase Churn Flow In A Vertical Pipe

The churn flow is an important flow pattern between the slug flow and the annular flow in the vertical pipe.Because of its complex flow pattern,it is also called "frothy slug".Owing to the instantaneous change of the proportion of gas and liquid in the cross section,the flow pattern has the characteristics of oscillation and pulsation.This kind of instability will cause damage to the parts in the process of power and heat transfer in the pipeline transportation.Because the churn flow widely exists in the gas-liquid two-phase flow,there is little research on the flow pattern in all flow patterns,so the exploration of the churn flow it has important research value and practical significance.In this paper,we use three-dimensional geometric model and structured mesh,and select Euler-VOF multiphase flow model,RNG k-e turbulence model and slip free boundary conditions.Fluent is used to simulate the gas-liquid two-phase churn flow in vertical pipe.The void fraction,liquid holdup and pressure drop of cross section and axial section under the condition of air and liquid water churn flow in vertical pipe are studied The change of gas-liquid velocity in the axial direction is simulated.It is observed that the flow parameters of the cross section fluctuate irregularly with time.The reason is that the gas phase moves upward with different amount of liquid phase in different time.The numerical curve shows that the average void fraction of the cross section increases rapidly with the increase of the apparent gas velocity,and decreases slowly with the increase of the apparent liquid velocity.Analysis the variation of void fraction,liquid holdup and gas-liquid velocity along the vertical pipe section along the pipe length is analyzed.The generation and development process of the churn flow is obtained through the analysis of the phase cloud atlas.The change of the parameters of the cross section is confirmed by comparing the phase cloud atlas under different working conditions,and the flow field and pressure distribution of the gas-liquid churn flow along the pipe rectangle under different working conditions are analyzed.The results of this paper are helpful to explain the movement process of gas-liquid two-phase churn flow in vertical pipe and the change rule of parameters,which has certain guiding significance.