The Mechanism Research Of Thermal Fluctuation Of Hot And Cold Fluids Mixing In Tee Junctions And Its Weakening

The tee junction is a typical structure type in pipe systems of nuclear power, coal-fired power and chemical industry, it is mainly used for connection, mixing and diffluence of fluids. When two kinds of fluids at different temperatures are mixed, due to the temperature difference between them, there will be strong temperature fluctuations on the pipe wall because of turbulence and buoyancy, it causes cracks on the pipe wall and even leads to thermal fatigue failure of pipes. So far, many pipeline damage accidents have occurred in nuclear piping systems because of the thermal fatigue phenomenon, so there are some academic value and practical significance to research how to reduce and weaken the temperature fluctuations on the pipe wall.In this paper, both of experimental and theoretical studies are used to study the effect of adding the branch liquid distributor on flow and heat transfer of hot and cold fluids mixing in the T-junction, the normalized mean temperature and the normalized RMS temperature of large-eddy simulation are in a good agreement with experimental results, it proves that the large-eddy simulation method is of some validity and reliability and it shows that the large-eddy simulation method could predict the temperature fluctuations of hot and cold fluids mixing in the T-junction with the liquid distributor.On the basis of validation of the large-eddy simulation turbulence model, the T-junction wall temperature fluctuations in different diameter ratios and velocity ratios of main pipe and branch pipe are simulated by the large-eddy simulation to study the effect of the branch liquid distributor. Firstly the trend of temperature fluctuations on the pipe wall in different jet types are analysed, secondly the effect of the liquid distributor in different direction of arrangement are researched. The numerical results show that the branch liquid distributor could weaken thermal fluctuations of pipe wall in the type of wall jet, but in the type of deflecting jet and impinging jet, the effect of the liquid distributor on weakening thermal fluctuations is limited. When the gravity direction is opposite to the direction of the flow in the main pipe, the branch liquid distributor could improve the efficiency of mixing in the T-junction.