Investigations Of Thermal Fluctuation And Its Weaken Mechanism In An Elbow Pipe With Thermal Stratification

In nuclear power plant pipeline system, T-pipe is a commonly used pipe structure. In T-pipe as the mixing of high and low temperature fluids brings temperature fluctuation, causing thermal fluctuations and thermal fatigue phenomena in the pipe, which also causing cracks in pipe and leakage accident due to thermal fatigue. In the world, the leakage accidents of nuclear power plant piping system due to thermal fatigue have occurred many times, which causing a widely attention in the field of nuclear power.Based on the research of the thermal stratifications’ flow and heat transfer mechanism in bent pipe, this work uses vortex breaker to weaken the thermal fluctuations and theraml stratifications in T-elbow, the effectiveness of vortex breaker is validated through the numerical simulation and experiment method. In numerical simulation, the temperature fluctuations process in the T-elbow with or without vortex breaker was established and solved by the Large Eddy Simulaiton(LES) numerical method using the FLUENT software platform, gained the informations of dimensionless average temperature and dimensionless RMS tmeperature in elbow. In experiment, the water was used as the working medium and the experiment of thermal stratification with or without vortex breaker was carried out in the T-elbow laboratory bench, the instantaneous temperature of each measuring points in elbow was measured and recorded by the thermocouple temperature sensor and the data acquisition system.After comparied the numerical results and experimental results of dimensionless average temperature and dimensionless RMS tmeperature, we found that they had a highly degree of agreement, which improved the reliability and validity of Large Eddy Simulaiton numerical method.The research results showed that the vortex breaker could weaken the thermal fluctuations of T-elbow effectively. On the basis of Large Eddy Simulaiton validation, we futher analysised and researched vortex breaker’thermal fluctuations weaken performance with the influence of different flow rates, the location of vortex breaker, the size of vortex breaker and the number of vortex breaker’leaves. The numerical research results showed that the thermal stratifications’location in T-elbow decreased with the increasing of thermal fluid velocity. Increased the number of the vortex breaker’leaves, deepen the location of the vortex breaker and increased the length of the vortex breaker were beneficial to weaken the thermal stratifications and thermal fluctuations in T-elbow.