Investigation of Thermal Fatigue in T-Junction Pipe

Abstract

The T-junction pipes are used in the cooling system of the nuclear power plants for the mixing of hot and cold fluid streams. There is cyclic variation in the temperature of the fluid near the junction. This cyclic variation is then transmitted to the pipe wall. This causes cyclic variation in the temperature and induction of thermal fatigue in the wall and the system can fail. The prediction of thermal fatigue is thus important for thermal mixing in T-junction pipes for a good design. The prediction of thermal fatigue requires the solution of the flow field and the temperature field in the flow as well as that of the temperature field in the pipe wall and subsequent prediction of the thermal stress in the pipe wall. There are parameters such as the velocity of the cold and hot streams, the diameter of the main and the branch pipe etc., that influence the thermal mixing in the T-junction pipe. Prediction of the effects of these parameters on the mixing is also important for a good design.

The aim of the present study is to investigate the effects of the aforementioned parameters on the thermal mixing and its subsequent effect on the thermal fatigue in a T-junction pipe. The objectives are to solve the concerned governing equations using numerical tools such as CFD. The flow and the temperature fields in the fluid as well as the temperature field in the pipe wall are predicted for different values of the parameters. Subsequently, the thermal stress in the pipe wall is predicted. The analysis is carried out for the thermal fatigue in the wall.