Experimental And Numerical Studies On Distribution Characteristics Of Mist Flow In Pipes

Pipeline mist flow is a common gas-liquid flow pattern in the gas-liquid transportation links in the fields of oil and natural gas exploration,chemical industry,boilers and nuclear reactors.The distribution of droplets in the mist flow directly affects the gas delivery efficiency and gas-liquid mixing levels.The predecessors’ research on the gas-liquid flow in pipes is mainly aimed at the flow pattern with high liquid holdup,while the research on the droplet is mainly carried out in the spray field or on the mechanism of the single droplet,and the research of mist flow in pipes has not been fully carried out.This paper mainly analyzes the mechanism of the influencing factors of the distribution characteristics of droplets in the mist flow in the pipes through experiments and numerical simulations,and studies and optimizes the distribution level of the pipeline flow field.The research content is mainly divided into the following two aspects:Firstly,based on the gas-liquid flow in pipes experimental platform and a highspeed imaging experimental platform,the mist flow droplet data is collected in multiple working conditions and multiple regions.According to the analysis of the experimental results,the following points are summarized:(1)At the section in the middle of the pipeline,the particle size of the droplets decreases with the increase of the apparent gas velocity of the pipeline,and the distribution of the droplets tends to be uniform;(2)The distribution of droplets is greatly affected by the foamy liquid layer at the bottom of the pipe,and the height of the foamy liquid layer loses aerodynamic force,which reduces the overall droplet size carried by the gas;(3)There are differences in the distribution of droplets in different spatial positions of the pipeline,which are affected by aerodynamic force,droplet gravity and drag,the droplet size in the axial direction gradually decreases;(4)Under the condition of no foamy liquid layer,the droplet particle size at the central axis in the radial direction in pipeline is the highest and the concentration is the lowest,and the droplet particle size at the position far from the central axis in pipeline gradually decreases,under the condition of foamy liquid layer,the droplet size is the lowest at the central axis of the pipe in the radial direction,,and the particle size increases near the pipeline wall;(5)Introduce the droplet characteristic diameter,distribution function and uniformity index m to evaluate droplet distribution level,and fit droplet particle size diameter correlation and evenness index prediction.Secondly,based on the CFD simulation modeling of the flow channel in the pipeline,and verify the reliability of the numerical simulation results with the experimental results,analyze the effect of the pipeline flow field on the gas phase and the droplets,the specific summary is as follows:(1)The radial gas velocity makes The unstable area in the flow field is the main reason for the unstable distribution of the pipeline foamy liquid layer and the droplet;(2)The radial velocity of the droplet causes the uneven distribution of the droplet concentration,and the droplet particle size is proportional to the velocity;(3)Optimize the structural parameters of the orifice plate of the pipeline: the number of holes n,the relative thickness t/d,the equivalent diameter ratio β,improve the gas distribution level,shorten the gas phase instability area,reduce the gas turbulence intensity,improve the gas phase uniformity in the pipeline and droplet distribution level.