Research On The Pressure Relief Process Of The Safety Valve By CFD Numerical Simulation

As one of the most important ways to ensure the safety of the system,safety valves are widely used in pressure vessel pipelines in various thermal power flelds.Researches on safety valves include experimental studies,auxiliary theoretical calculations and numerical simulations currently.Due to the limitations of the environment in which the safety valve located,this paper combined the results of the pressure relief characteristics test of the safety valve during the maintenance period of a nuclear power plant.It used the numerical simulation method to evaluate the pressure and temperature in the main steam pipe on the opening time of the main valve of the safety valve by setting different process system parameters.According to the results,the potential reasons for the valve opening timeout were analyzed and discussed and guidances for the operation,commissioning,testing and maintenance of the valve were provided.In addition,the transient pressure relief characteristics of high temperature steam safety valve and the factors affecting the pressure relief characteristics were investigated by the complex time-varing topology dynamic mesh numerical method.Thereby,the structure of the safety valve was improved to achieve the optimization of the design.The simulated object was the SE280 type valve,which is a spring loaded safety valve,including a pilot solenoid valve and a main valve.A three-dimensional model of the safety valve was established to simulate the transient pressure relief characteristics of the safety valve during the pressure-release stage of the pilot solenoid valve relief stage(when the disc was in a static state).The flow field characteristics(pressure fields,temperature fields,velocity fields and Mach number)of different cross sections in the safety valve and the mass flow rate of the inlet and outlet were studied.The degree of effect of key structural parameters in the safety valve on the main valve opening time was quantitatively studied.It was found that the area where the solenoid valve pressure relief orifice(the orifice D)and the vertical tube connected has the greatest influence on the main valve opening time.The flow field parameters in the safety valve changed drastically in the local area,and the supersonic flow occurred,resulting in the shock wave phenomenon.Using CFD simulation method,the complex dynamic mesh deformation technology was customized to simulate the valve pressure relief process.The dynamic pressure relief characteristics of high temperature steam safety valve and the dynamic characteristics of the disc were studied.The dynamic characteristics of the disc were studied under different inlet pressure conditions:the main valve opening time became longer as the inlet pressure increased.The operating time of the disc can reach the maximum opening height in several tens of milliseconds.The full opening flow rate of the safety valve had a great relationship with shapes of the disc.According to the results in the literature,the shape of the disc in the geometric model of the safety valve in this paper was in good agreement with the results.The accuracy of the numerical simulation results was also verified.The influence of different superheat,turbulence models and working fluids on the transient pressure relief performance of the valve was studied by using the control variable method and the deformed dynamic mesh technique.The realizable k-?turbulence model and the increase of the steam superheat can make the safety valve open quickly.The safety valve full opening time of with the natural gas as working medium is similar to that of water vapor,which provided the possibility for subsequent safety valve experiments.The flow field characteristics of the lower outlet pipe of the disc were also studied under different opening degrees.When the opening height was within 60 mm,the parameters in the outlet flow path were greatly affected by the area between the disc and the sealing surface of the valve.When the opening height was greater than 60 mm,it was greatly influenced by the extermal atmospheric environment,and the change of the outlet flow field parameters was not obvious compared with the previous stage.