Flow Field And Thermal Stress Analysis Of Gate Valve In Transient Condition

The fourth-generation reactor technology puts forward higher requirements for the safety of the reactor.The main gate valve is an important component of the reactor's primary circuit system and its structure is relatively complex,so there are many factors to be considered in the design.The main gate valve is an important structure on the flow channel,which is responsible for flow rate adjustment and other important tasks.In certain transient processes,the main gate valve may have to withstand rapid changes in flow and temperature,which will cause rapid changes in the internal stress field and the temperature field of the valve body and create additional thermal stress.This will have an impact on the deformation and sealing of the gate valve,which need to be clarified during design.Under transient conditions,it is sometimes impossible to control the thermal stress within the allowable range of the traditional standard.Therefore,the thermal stress may exceed the allowable value and may cause the sealing failure of the gate valve,which is not allowed.In this paper,Computational Fluid Dynamics method is used to conduct transient three-dimensional fluid-structure coupling analysis of gate valve including part of piping system.First,the complete geometric model of the system is built,then the selection of the turbulence model is analyzed.The flow field and the secondary flow in the gate valve under steady state are analyzed and compared in detail using Reynolds stress model(RSM)and Standard k-? model.It is verified that the standard k-? model combined with the scaled wall function can analyze the flow field and secondary flow in the gate valve accurately.Through the transient numerical simulation,the temperature field,the thermal deformation and thermal stress are obtained.In the transient process,the secondary flow intensity in the gate valve will increase,which will enhance the heat exchange between the valve body and the fluid.The average temperature of the gate valve will drop by 10.47K during the transient process.The thermal stress on the outer surface of the gate valve is lower,and the thermal stress in the middle of the gate valve reaches 100MPa.The thermal stress on the wall that directly exchanges heat with the fluid inside the gate valve is relatively large.In the transient process,the maximum additional thermal stress reaches 246.46 MPa,which is located on the wall near the junction of the upper chamber and the internal flow channel of the gate valve.The middle and upper parts of the gate valve deform greatly.The maximum deformation reaches 0.242mm,which is located on the bonnet of the gate valve.The closer to the bonnet of the gate valve,the greater the deformation.On this basis,different boundary conditions and different valve structures are analyzed and evaluated for investigating decreasing the deformation.By comparing the calculation results of different working conditions,because the flow rate of the branch pipe is small,changing the time of injecting the hot fluid into the branch pipe has little effect on the change of the temperature field and stress field in the gate valve.In comparison,moving the branch pipe position,using the orifice plate to increase mixing,and adding a baffle inside has very limited influence on the change law and value of the valve body temperature.That is to say,the thermal stratification phenomenon formed by improving the temperature of the branch pipe and the main pipe is not effective,only by changing the structure of the valve body,such as reducing the gap between the valve plate and the valve body in the first improvement measure,can have a relatively significant effect.Therefore,through the research in this article,it can be seen that if the deformation of the valve body is to be reduced,it is necessary to design carefully of the valve body structure.The results can be used as a reference for the design of the gate valve that need to withstand rapid temperature changes.