Research On The Flow And Heat Transfer Of Thermal Stratification In An Injection Pipeline Of Steam Generator

Kinds of pipes exist extensively in nuclear power plants. Because of the temperature differences of fluids in pipes, it may cause thermal stratification. Thermal stratification is an important reason causing pipes thermal fatigue, which may lead to pipe fatigue failure and rupture and it would badly affect nuclear power plant safety operation. Investigators had paid close attention to many pipe rupture accidents happened in the past, and did extensive research on pipe system safety.In this research, water flow in an injection pipeline of steam generator in power plant has been simulated using Large Eddy Simulation method and fluids velocity and temperature over time has been obtained. By comparison of simulation results and experiment data, well agreement was found between the two, and the LES method was validated, which laying foundation for further study on thermal stratification flow and heat transfer. Large Eddy Simulation results show that the speed of cold water at the bottom of the horizontal section is higher than the speed of hot water at the top. With increasing the height of the cold fluid field, hot water is remaining at the top of the pipe and the thermal stratification keeps for many time because it is controlled by almost all cold water in the water exit holes.On the basis of validation of LES method, simulation results of temperature contours and velocity vector of five different conditions were obtained by changing inlet clod water mass flow rate and temperature difference between the cold and hot water. Following are temperature variation analyzed:temperature variation of monitoring points in different planes, temperature change over time along diameter direction, temperature variation of different monitoring points at the same level in the same plane and Temperature difference between the highest position and the lowest position.The results show that velocity and temperature difference both influence secondary flow cooling effect on pipe center. Different velocity and temperature difference have great influence on cooling velocity of fluids in pipe, temperature decrease amplitude, thermal stratification thickness and cooling sequence of upstream and downstream of planes.