Study On The Flow And Heat Transfer Of Vortex Generator To Enhance Heat Transfer

It is one of the most widely used passive enhanced convection methods to design vortex generators on the inner surface of heat exchange pipes for convection heat transfer.Vortex structure is generated when the fluid passes through the heat exchange pipe equipped with vortex generator?VG?,which results in the destruction of the fluid boundary layer,so as to enhance the heat exchangeIn this paper,large eddy simulation?LES? is the main method,and particle image velocimetry?PIV?experiment is the auxiliary method.First,the feasibility of using the large eddy simulation method to obtain the subtle vortex structure and flow image behind the vortex generator in turbulent flow is studied.Then,the arc and trapezoidal vortex generators with different angles of attack are arranged in the rectangular channel to study their The influence of flow field and heat transfer and the interaction mechanism between flow and heat transfer.Details are as follows:?1?Effect of vortex generator on flow field:by studying the distribution of vortex structure,vortex intensity and velocity,turbulent kinetic energy and turbulent dissipation rate in the flow field,the flow field changes caused by vortex generator can be visualized.The results show that there are four types of vortex structures behind the vortex generator.The positions of the four types of vortex structures are different in space,and different vortex structures have different contributions to heat transfer enhancement.The strengthening effect of primary vortex pair is better than that of secondary vortex pair,and the hairpin vortex pair can maintain the existence of reverse vortex pair better,so as to improve the heat exchange effect.?2?The effect of vortex generator on heat transfer:the effects of different Reynolds number and angle of attack on the enhanced heat transfer characteristics of vortex generators are explored,the heat transfer enhancement effect?the increase of Nusselt number?and flow resistance are recorded.The flow resistance characteristics,enhanced heat transfer performance and comprehensive heat transfer performance of the vortex generator are described by dimensionless numbers of f/f₀,Nu/Nu₀ and PEC respectively.At the same time,the expressions of Nusselt number and resistance coefficient for the structure parameters and flow parameters of vortex generator are fitted.The results show that the heat transfer enhancement effect increases with the increase of angle of attack and Reynolds number;the trapezoidal vortex generator with an angle of attack of 45°shows the best heat exchange effect and comprehensive performance in all working conditions,that is,PEC can reach 1.65-1.43;under the condition of the same attack angle,the heat transfer effect of trapezoidal vortex generator in rectangular channel is better than that of arc vortex generator.?3?Flow characteristics and heat transfer characteristics of vortex generators to enhance heat transfer:the vortex structure and the distribution of Nusselt number are compared,and the influence of the secondary flow intensity on the heat transfer effect and the field synergy theory are analyzed to reveal the flow characteristics of the vortex generator and the interaction mechanism between the heat transfer characteristics.The results show that the vortex structure is in good agreement with the normal temperature gradient distribution,indicating that the Hairpin Vortex has a great effect on heat transfer in the normal direction;the larger the secondary flow intensity is,the better the heat transfer is,and the larger the resistance coefficient in the rectangular channel is;based on the analysis and comparison of the local field synergy angle?and Nusselt number Nu of the rear section of the rectangular channel vortex generator,it is found that the Nusselt number in the region with smaller field synergy angle is larger;the vortex structure induced by vortex generator can improve the coordination of velocity field and temperature gradient field,and ultimately affect the heat transfer effect.This paper has 35 pictures,8 tables,and 65 references.