Study On Axial And Radial Distribution Characteristics Of Cavitation Flow Inside Coal Liquefaction Control Valve

Due to the lack of oil resources and the relative abundance of coal resources,coal liquefaction technology can realize the clean and efficient utilization of coal and oil substitution,which is an effective way to alleviate the energy crisis in China.The coal liquefaction control valve is the core component of the coal liquefaction process system,which is often subject to serious cavitation and cavitation / wear damage,reducing its service life.Therefore,in this paper,theoretical analysis,numerical calculation and experimental research methods are used to study the cavitation flow phenomenon and axial and radial flow distribution characteristics of coal liquefaction control valve.In view of the theoretical research on cavitation flow of the control valve,the throttling principle and flow characteristics of the control valve are analyzed.Through the numerical simulation and theoretical formula calculation of the flow characteristic curve of the control valve to be studied,it is concluded that the flow characteristic of the control valve belongs to parabolic type,and the flow capacity increases with the increase of the opening.Based on the basic mathematical model of CFD and the established calculation model of control valve,the flow field characteristics inside the control valve are obtained by simulation.An experimental and cavitation image acquisition system is built,and the visualization technology of flow field is used to capture the cavitation shape.The correlation analysis of cavitation image is carried out by image post-processing technology,and the standard deviation and average value images with the superposition number of cavitation image of 80 are obtained.With the help of the change rule of gray value in the standard deviation and average value image,the axial distribution,axial development and axial distribution characteristics of cavitation flow field in the control valve are analyzed.The results show that with the increase of inlet pressure,cavitation occurs at the valve port and expands to the downstream.The distribution form of cavitation area develops from the inception,collapse area to the inception,development and collapse area of cavitation The length of cavitation axial development increases with the increase of inlet pressure.cavitation is essentially caused by low pressure.The low pressure area is conducive to the development of cavitation,and the occurrence of cavitation enhances the intensity of fluid turbulence.The radial development process of cavitation,the distribution of cavitation flow field and the flow characteristics are analyzed by numerical simulation.With the increase of inlet pressure,the radial development of cavitation ring can be divided into three stages: no cavitation,cavitation formation and cavitation stabilization.The pressure distribution downstream the valve decreases with the increase of inlet pressure,but remains unchanged in the cavitation stabilization stage.The cross-section velocity,cavitation and turbulence intensity increase with the increase of inlet pressure,and the formation of cavitation ring leads to the sudden increase of average velocity.Cavitation results in the increase of fluid energy loss,Reduce the valve flow capacity.The thesis has 63 figures,3 tables and 98 references.