Numerical Study On Laminar Flow And Heat Transfer Characteristics In Circular Tube With Different Twisted Vortex Generators

Nowdays,the problem of energy is become more and more tight,it promoted the heat exchanger to light weight and low loss,at the same time,the heat transfer enhancement technology in tube has been rapidly developed.The twisted tape is the simplest interpolating spoiler element,which is widely used to enhance the heat transfer inside the tube.It is very effective for enhancing the convective heat transfer of low Reynolds number fluid or high Prandtl number fluid,but it also increases the pressure drop and resistance of fluid in the tube.In order to reduce the frictional resistance and body resistance of the fluid in the tube,a twisted winglet vortex generators is obtained by modifying the twisted tape,on this basis,a twisted hollow vortex generators is proposed.In this paper,the laminar flow and heat transfer in a tube with different shapes of twisted vortex generators are firstly simulated by numerical method.The effects of different shapes of vortex generators on the fluid flow and heat transfer in the tube are compared.The influence of the structural parameters of the isosceles trapezoid vortex generators on the fluid flow and heat transfer in the tube is further analyzed.The fluid flow and heat transfer characteristics of the hollow vortex generators inserted in the tube were studied.The effects of different inserts element on the fluid flow and heat transfer in the tube were compared.The relationship between the secondary flow intensity and the convective heat transfer in the tube with different inserts element were analyzed.The study showns that:(1)When the area of the twisted tape cut off is equal,the shape of the vortex generators has a certain influence on the convective heat transfer in the tube.The heat exchange capacity of the isosceles trapezoidal vortex generators is best,followed the right angle trapezoidal vortex generators,rectangular vortex generators have the worst heat transfer capacity.(2)After inserting different shapes of vortex generators in the tube,the fluid flow is fully developed in the cross section along the main flow direction in the range of x = 0.29 ~ 0.333 meter,and the average Nu number in the cross section along the main flow direction changes periodically.(3)For the isosceles trapezoidal vortex generators,with the same structural parameters except the vortex generators twisted rate or the vortex generators spacing,the average Nu of the isosceles trapezoidal vortex generator decreases as the vortex generators twisted rate or the vortex generators spacing increases.For the twisted hollow vortex generators,with the same structural parameters except the vortex generators twisted rate,the average Nu and the drag coefficient f of the twisted hollow vortex generators decrease as the vortex generators twist rate increases.(4)After inserting different inserts element in the tube,the comprehensive heat transfer enhancement capacity of the hollow vortex generator is the best in the range of Re = 50 ~ 200,and the vortex generators is the worst;In the range of Re = 200 ~ 800,the comprehensive heat transfer enhancement capacity of the hollow twisted tape is the best,and the vortex generators is the worst.(5)For the isosceles trapezoidal vortex generators,with the same structural parameters except the vortex generators twisted rate or the vortex generators spacing,the secondary flow intensity in the tube increases as the vortex generators twisted rate or the vortex generators spacing decreases;The variation of the based tape width of the isosceles trapezoidal vortex generators has no obvious dependence on the change of the secondary flow intensity in the tube.For the twisted hollow vortex generators with the same structural parameters except the vortex generators twisted rate,the secondary flow intensity in the tube increases with the decrease of the twisted hollow vortex generators’ twist rate;as the twist ratio of the hollow twisted tape decreases,the secondary flow intensity in the tube increases.