Experimental Study On Thermal Mixing Characteristics Of Cold And Hot Flows In The T-junction

The T-junction is one of the most basic fluid transmission and distribution components in industrial production.As the connection between pipelines,it is often used for the diversion and confluence of working fluid in pipelines.It plays an important role in many fields such as nuclear power and chemical industry.When two fluid streams with different temperatures are mixed near the surface of the pipe structure,periodic fluctuations or layered thermal stresses will occur on the pipe wall,resulting in thermal failure of the pipe material.The research on the temperature fluctuation mechanism of the T-junction hot and cold fluid mixing process and the temperature fluctuation characteristics of the hot and cold mixing under different influence prime conditions have always been the research hotspots of scholars.This paper summarizes the research on the mixing process of hot and cold fluids in the T-junction firstly,including the research contents and results of domestic and foreign scholars on the temperature distribution and temperature fluctuation characteristics of the mixing process by experiments and simulation methods.At the same time,the thermal fatigue mechanism and mixing flow pattern of the hot and cold fluid mixing process in the T-junction were analyzed.A visualized experimental bench for hot and cold mixing is set up to analyze the influence of various influencing factors on the temperature characteristics of the hot and cold fluid mixing process in the T-junction through experimental research.Based on the different flow and heat transfer characteristics of the fluid,related experimental studies including different momentum ratios and temperature differences are conducted,and the development process of mixed flow patterns is analyzed to obtain the normalized mean temperature and the normalized root mean square under each working condition.Regular characteristics of temperature distribution and temperature fluctuation amplitude and frequency.The results show that the momentum ratio has a great influence on the normalized mean temperature distribution of the hot and cold mixing process,and as the momentum ratio increases,the temperature fluctuation intensity will be more severe,and the mixing length will be significantly reduced.The increase of the momentum ratio will also cause the amplitude and frequency of the most severe temperature fluctuations of the mixing pipe section to increase.At the same time,the increase in temperature difference has almost no effect on the normalized mean temperature distribution of the mixing pipe section.The effect of the change in buoyancy caused by the temperature difference on the intensity of temperature fluctuations during the mixing of hot and cold fluids is also very weak.In addition,related experimental studies were conducted under the structural conditions of different injection angles and injection positions.The development process of mixed flow patterns and the characteristics of the value and frequency were analyzed.The results show that different injection angles have a great influence on the normalized mean temperature distribution.When the incident angle is 45°,the mixing degree and temperature fluctuation degree are weaker than when the incident angle is 90°,and the mixing length increases significantly.Different injection positions have no significant effect on the normalized mean temperature distribution and mixing length of the branch pipe injects from above the main pipe(UP)and the branch pipe injects from below the main pipe(DW).In the wall jet stage,the degree of temperature fluctuation when the branch pipe injects from below the main pipe(DW)is greater than when the branch pipe injects from above the main pipe(UP);in the deflected jet and impinging jet stage,the degree of temperature fluctuation when the branch pipe injects from below the main pipe(DW)Less than when the branch pipe injects from above the main pipe(UP),but the changes in positions have a very limited effect on the temperature fluctuation.This paper researches the temperature characteristics of the hot and cold fluid mixing process in the T-junctions under different factors,and provides strong support for the optimization of safe and stable operation of the pipeline.It lays the foundation for avoiding thermal fatigue accidents and improving pipeline service life and has great scientific and practical significance.