Numerical Study Of The Characteristics Of Flow And Heat Transfer Of Oil Flowing In A Circular Tube Inserterd With Vortex Generators

Heat exchanger is widely applied in all kinds of industrial equipment.It is not only an indispensable part to ensure the normal operation of engineering equipment,but also plays an important role in energy consumption,power consumption and investment.The heat transfer ability of heat exchanger is an important standard to evaluate the heat exchanger.How to improve the heat transfer ability of heat exchanger has become one of the most significant research topics.Therefore,it is an inevitable trend to strengthen heat transfer of heat exchanger.The heat transfer enhancement technology can improve the heat transfer capability of heat exchanger,which is mainly realized by increasing heat transfer area,using the interposed flow element and changing the characteristics of working medium.The use of a spoiler is the most common technique for enhancing heat transfer.Based on this background,this thesis investigates the flow and heat transfer of lubricating oil in a tube with a coaxial cross vortex generator.Moreover,based on the study of coaxial cross vortex generators,regular interval coaxial cross vortex generators and hollow coaxial cross vortex generators are proposed.The effects of the shape,twist ratio Y,pitch S_n and base-band width D₀ of the coaxial cross-vortex generator on the flow and heat transfer of lubricating oil in the tube are studied in detail,and the relationship between the secondary flow intensity and convection heat transfer is analyzed.Meanwhile,the effects of the spacing of regular-spaced coaxial cross-vortex generators and the torsion ratio of hollow coaxial cross-vortex generators on the flow and heat transfer of lubricating oil in the pipe are investigated.The results are as follows:（1）The heat transfer of lubricating oil in the tube is enhanced by inserting different shaped coaxial cross vortex generators.The order of heat transfer enhancement of vortex generators is isosceles coaxial cross vortex generators,right angle trapezoid coaxial cross vortex generators,parallelogram coaxial cross vortex generators and rectangular coaxial cross vortex generators.（2）The flow of oil in the tube is fully developed in the range of x=0.315m～0.353m,and the mean nusselt number varies periodically.（3）The mean nusselt number Nu increases with the increase of Reno number Re,and the drag coefficient f decreases with the increase of Reno number Re,when the torsion and spacing of the isosceles trapezoid coaxial cross vortex generator are fixed,and the heat transfer enhancement factor JF and the secondary flow intensity Se increase with the increase of Re.When Re is fixed,with the decrease of the torsion ratio and the distance,the heat transfer enhancement factor JF increases,and the secondary flow intensity Se in the tube increases.（4）The average Nu of regular-spaced coaxial cross-vortex generators is 2.51 times of the average Nu of smooth tube,and the flow resistance is 2.25 times of smooth tube.（5）At the same torsion rate,with the increase of Re,the average Nu number of the hollow coaxial cross-vortex generator increases,and the drag coefficient f decreases.At the same time,the maximum average Nu number of the hollow coaxial cross vortex generator is3.51 times that of the optical tube.The heat transfer enhancement factor JF is greater than 1,indicating that the hollow coaxial vortex generator inserted in the tube can effectively enhance the heat transfer of lubricating oil.