Numerical Study On Heat Transfer Enhancement By Curved Vortex Generators In The Heat Exchange Channel

Installing the vortex generator in the heat exchange channel is an efficient and passive method to enhance heat transfer.The vortex generator destroys the boundary layer by generating longitudinal vortex,so that the fluids are better mixed and achieve the purpose of enhancing heat transfer.The angle of attack,height,shape,location and curvature of the vortex generator affect the intensity of the longitudinal vortex.At present,there are few researches on curved vortex generators,and even less research on curved delta winglet vortex generators.The study of the curvature of the curved delta winglet vortex generator of equal arc length on the plain fin and the location of the curved delta winglet vortex generator on the tube-fin has not been reported.Therefore,this paper numerically studies the effect of the curvature of the curved delta winglet vortex generator on the heat transfer performance of the plain fin,and it turns out that there exists an optimal curvature of the vortex generator to make the fin has the best heat transfer performance.In addition,the influence of the transverse location and longitudinal location of the curved delta winglet vortex generator on the heat transfer performance of the tube-fin is also studied.This paper shows the following results through numerical simulation:This paper studied the effect of the curvature of the curved delta winglet vortex generator on the heat transfer of the plain fin.The results show that the change of curvature affects the heat transfer and flow characteristics in the flow channel of the heat exchange.The heat transfer performance of the concave vortex generator is stronger than the straight vortex generator,and the heat transfer performance of the straight vortex generator is stronger than the convex vortex generator.The vortex generator with the best curvature can optimize the heat transfer and flow characteristics of the plain fin.Compared with the smooth channel,the Nusselt number and thermal performance evaluation factor JF of the vortex generator with the best curvature increased by 34.4% and 16.5%,respectively.The maximum difference between different curvature of the Nusselt number and the thermal performance evaluation factor is22.9% and 11.2%,respectively.Numerical study of the influence of the transverse location of the curved delta winglet vortex generator on the heat transfer of the tube-fin shows that different transverse location has different performance on the heat transfer of the tube-fin.When the vortex generator moves upward from the original transverse location,the average Nusselt number and the heat transfer evaluation factor JF decrease gradually,which means that the upward movement of the vortex generator is not conducive to heat transfer.When the vortex generator moves downward from the original transverse location,Nu and JF decrease gradually at low Reynolds number,and Nu and JF first increase and then decrease at high Reynolds number.There is an optimal transverse location of the fin to achieve the best heat transfer performance.Compared with the original location,Nu and JF increased by 1.28% and 1.38%,respectively.The maximum difference between Nu and JF in different transverse locations is 16.9% and16.0%,respectively.Numerical study on the effect of the longitudinal location of the curved delta winglet vortex generator on the heat transfer of the tube-fin shows that the longitudinal vortex intensity and heat transfer are obviously affected by the longitudinal location of the vortex generator.The vortex generator has the best longitudinal location to achieve the greatest heat transfer performance.Compared with the smooth channel,the Nusselt number Nu and the friction coefficient f at the optimal longitudinal location increased by 15.2%~43.9% and12.2%~15.7%,respectively.Compared with the original location,the Nusselt number and friction coefficient increased by 5.4%~9.8% and 4.8%~12.2%,respectively.Compared with the original location,the thermal performance evaluation factor increased by 8.1%,and reached to 1.38.There is a good correspondence between the Nusselt number and the intensity of the longitudinal vortex,which means that the intensity of the secondary flow determines the heat transfer.The results are of great significance in the design and optimization of the fin-tube heat exchanger of the studied curved delta winglet vortex generator.