| In the coal liquefaction project,the control valve is the key control element in the entire system.Because the control valve has been working in an environment of high temperature and large pressure difference for a long time,and it is also subject to cavitation and erosion,it has a short service life,which seriously affects the development of coal liquefaction technology.Therefore,this paper uses a combination of numerical simulation and experimental research to study the distribution characteristics of the flow field in the control valve and the erosion characteristics of the spool and seat of the control valve.Based on the CFD numerical simulation theory,a simulation calculation model of the coal liquefaction control valve is established.Three typical flow fields of control valve are studied by combining the hydrodynamic equation and mathematical model.A visualization experiment platform was built,and the real flow of fluid in the control valve was observed combined with particle image velocimetry technology.The numerical and experimental methods are used to study the velocity and pressure distribution characteristics of the fluid quality in the flow field of the regulating valve.It is found that in the flow field of the control valve,the high-speed area is mainly distributed in the orifice and the middle area of the throat,and the low-speed area is distributed in the expansion section and the outlet area.Downstream of the spool head,there is a medium backflow vortex caused by the reverse pressure gradient.Pressure difference and opening degree are important factors that affect the axial and radial distribution characteristics of velocity and pressure in the flow field.With the change of the pressure difference between the inlet and outlet of the control valve,the velocity in the flow field increases with the increase of the pressure difference,and the area of the return vortex downstream of the spool head also increases with the increase of the pressure difference.As the opening of the control valve increases,the fluid velocity in the flow field shows an overall increasing trend;the pressure distribution remains basically unchanged.When the control valve is in operation,the medium in its flow field will inevitably contain a certain amount of solid particles,and the solid particles will cause erosion damage to the spool and seat of the control valve.The study found that the most severely abraded part of the spool head is the top of the arc section of the spool head,followed by the parabolic section.The more severely abraded area on the valve seat wall is located at the orifice and the junction between the seat throat and the expansion section.The damage on the parabolic section of the spool head is mainly cutting wear,and the damage on the top of the arc section is the result of the combined effect of cutting wear and deformation wear.On the wall of the valve seat,before the contraction section,the damage on the valve seat wall is mainly caused by cutting wear,and after the contraction section,it is caused by the combined action of cutting wear and deformation wear.In addition,considering the four factors of control valve opening,pressure difference between inlet and outlet,erosive particle size and particle concentration,an orthogonal experiment was designed.It is found that the two factors that have the greatest influence on the wear rate are the erosive particle size and the pressure difference between inlet and outlet.Changing the particle size basically has no effect on the distribution characteristics of erosion damage,and the erosion rate will increase with the increase of the particle size.When the pressure difference increases,the obstructive effect of fluid inertial force and cavitation will reduce the erosion rate on the wall of the spool and valve seat in cavitation area,and the erosion rate of the remaining parts will increase with the increase of the pressure difference.The thesis has 55 figures,5 tables and 90 references. |
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