| Spring Loaded Pressure Safety Valve(SLPSV)is an important safety accessory in the energy field and is the last barrier to ensure the safety of a pressure system.SLPSVs are widely used for overpressure protection of pressure vessels,pipelines,and important actuators.However,in practical applications,SLPSVs often face a series of failure problems such as valve disk jamming,sealing surface damage and spring fatigue,which seriously threaten the performance and safety of the pressure system.Existing research believe that dynamic instabilities of the SLPSV,such as valve disk ’flutter’,’chatter’ or ’low frequency cycling’,are the main causes of these failures.To explore the mechanism and suppression strategy of these dynamic instabilities,both experimental and numerical studies were performed on a SLPSV with a typical structure and its associated Pressure vessel-piping-safety valve(PVPSV)system in this paper.The details are as follows:1)Steady and dynamic experiments on the SLPSV/pressure system was carried out.In the steady state experimental study of the SLPSV,the influence of key valve parameters on the fluid disk force and the valve flux is studied,the results show that the fluid disk force changes stepwise with the increase of the valve opening upon certain valve configurations.In the dynamic experimental study of the pressure system,the dynamic responses of the pressure system under different valve configurations were tested,and based on the test results,the impacts of valve setting pressure and spring stiffness on the dynamics of pressure system were analyzed.2)A CFD(Computational Fluid Dynamics)simulation model for the SLPSV/pressure system is constructed.In the development of steady-state model of the SLPSV,by compared to the experiments,the SST(Shear Stress Transport)k-w turbulence model and 2-D axisymmetric mesh model were confirmed to be the optimal choice for the calculations of fluid disk force and valve inlet flux;Based on the simulation results of this optimal model,the mechanism of the "discontinuous fluid disk force" found in the steady-state experiments is analyzed;in the dynamic model development of the pressure system,a system-level simulation model which is based on dynamic mesh,UDF(User Defined Functions)and equivalent pressure point theory,was constructed,and its accuracy has been verified through experiments.3)A system-level reduced-order model of the SLPSV/pressure system is constructed.In view of the multi-parameter,multi-dimensional,strong coupling,and non-linear characteristics of the SLPSV/pressure system,approaches of the equivalent pressure point,the Method of Characteristics(MOC)as well as the surrogate model are used to simplify the models of pressure vessel,the connecting pipe and the SLPSV,respectively.Based on the simplifications mentioned-above,a system-level reduced-order model for dynamic response fast calculation of the pressure system is constructed.4)The inducing mechanism of the dynamic instabilities and a method of design optimization of the SLPSV/pressure system is revealed and proposed,consecutively.Based on results of the parameter sensitivity analysis and the system-level CFD simulations of the pressure system,the "pressure in front of the valve cannot be quickly restored due to long connecting pipelines" and "the large spring force between the spring force and the fluid disk force under large spring stiffness valve configuration" were considered to be the main causes of the dynamic instabilities of the SLPSV/pressure system.To suppress dynamic instabilities of the SLPSV/pressure system,a design optimization method which is based on surrogate models is proposed and design optimization of the pressure system was carried out.Through verification,the optimized pressure system can remain stable,meanwhile,the blowdown of the SLPSV can be reduced to 2.77%. |
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