Study On Flow-induced Vibration In High Temperature And Pressure Pilot-operated Steam Traps

This thesis is completed with the funding from the Ministry of Science andTechnology Project Personnel Service Corporate Actions “the research and develop-ment of high temperature, high pressure and ultra-high capacity inverted bucket pi-lot-operated steam traps”(NO:2009GJG10005). Steam trap is widely used in steamheating and steam pipe network as a kind of self-control valve. With the developmentof technology and the expansion of the industrial scale, industrial production hasshowed the trends of large capacity, high parameters, high efficiency and low con-sumption. The demand for working pressure, temperature and capacity has increas-ingly risen. However, under high temperature and high pressure conditions, the vibra-tion problem of pilot-operated steam trap is prominent, especially the severe vibrationof the piping system, result in wear of valve components and stem fracture phenome-non. It seriously affects the device’s safety and service life, as well as the physical andmental health of operator. In response to this situation, a series of studies were carriedout with the high temperature, high pressure and ultra-high capacity inverted bucketpilot-operated steam traps developed by Lanzhou University of Technology and GansuHongfeng Machinery Co.Ltd as the study object, which provide reliable references forthe pilot-operated steam trap with noise elimination, vibration damping and capabilitychoiceness.(1) The principle of flow-induced vibration and vibration in the pilot-operatedsteam traps were analyzed, the preventive measures of vibration were put forward. Thegeneral structure and working principle of the high temperature and pressure invertedbucket pilot-operated steam traps were introduced. Then, an equal percent flow regu-lating sleeve and a two-stage throttle cover were designed in the limited space of valveto reduce the noise and fluid erosion of seal surface on valve seat and core, preventcavitation and alleviate the vibration of valve and pipeline system.(2) Based on the force analysis of inverted bucket pilot-operated steam traps inthe critical opening and closing conditions, the static mathematical model was estab-lished, the range of spring force in critical conditions was determined. Based on dy-namic principle, the dynamic mathematical model of inverted bucket pilot-operatedsteam traps was set up, the influences of structure parameters on the dynamic per-formance of the steam trap was obtained. The conclusions can provide theoretic guid-ance for the further optimal design of the pilot-operated steam traps’ stability in future. (3) Three-dimensional model of the inverted bucket pilot-operated steam trap wasset up by using Solidworks software, three-dimensional numerical simulation of theinternal turbulent fluid field was performed by using Fluent of computational fluiddynamics software. The distribution of internal pressure field, velocity field and ve-locity vector field in each section and the export speed curve under different openingwas obtained. The flow rate regulating property and export velocity variation of steamtrap with flow rate regulating sleeve or without flow rate regulating sleeve in the steamtrap were analyzed comparatively, and the change law of the pressure field, velocityfield and velocity vector field in the steam trap with throttle sleeve or without throttlesleeve were also analyzed.(4) Valve core modal was analyzed by using finite element software ANSYS/Workbench, the influence of fluid-solid coupling, spring prestress, different slenderratio and different restriction which act on modal frequencies and vibration mode ofvalve core were explored.