Vortex Dynamics And Its Relationship With Heat Transfer Characteristic In A Bundle Of Spirally Serrated Annular Fins

Tube fin heat exchanger has been widely used in industrial production,and its potential efficiency has attracted much attention in recent years.As an important part of tube fin heat exchanger,spiral serrated annular finned tube is widely used in large industrial boilers,economizers and other industrial equipment.The spiral serrated annular finned is developed from the spiral annular fin.Compared with the continuous fin,the spiral serrated annular finned tube has severe disturbance in the channel,better turbulence condition,higher efficiency and better heat transfer ability.However,the numerical study on the vortex dynamics characteristics of spiral serrated annular finned tubes is rare,and the influence of the vortex dynamics characteristics on the heat transfer characteristics is less concerned.In order to explore the characteristics of vortex dynamics and heat transfer in the channel composed of spiral serrated annular fin single tube and tube bundle,and the relationship between the characteristics of vortex dynamics and heat transfer,the channel composed of spiral serrated annular fin single tube and tube bundle was studied.This dissertation,the unsteady calculation of three-dimensional spiral serrated annular finned tube is carried out by numerical simulation.Four turbulence models and two wall functions are selected to simulate the circular finned tube.The results are compared with those of other scholars.The results show that SST k-ωturbulence model is the best,and can accurately capture the Kármán vortex street behind the finned tube,and predict the heat transfer and pressure drop characteristics;After the verification of numerical method,firstly,the vortex dynamics and heat transfer characteristics of spiral serrated annular fin single tube under different structural parameters（fin spacing and fin height）are simulated respectively.The vortex dynamics and heat transfer characteristics of spiral serrated annular fin single tube under different structural parameters are studied,The relationship between the vortex dynamics and the heat transfer characteristics is analyzed.Secondly,the vortex dynamics and heat transfer characteristics of spiral serrated annular fin tube bundle under different longitudinal tube spacing are simulated respectively.The vortex dynamics and heat transfer characteristics of spiral serrated annular fin tube bundle under different longitudinal tube spacing are studied,and the relationship between the vortex dynamics and heat transfer characteristics of the finned tube bundle is analyzed.（1）When Re is fixed,the f and St of spiral serrated annular fin single tube increase with the increase of fin spacing;f and St decreases with the increase of fin height.The f of spiral serrated annular fin tube bundle increases first and then decreases with the increase of longitudinal tube spacing;When Re<10000,St decreased with Re,and then gradually slowed down with Re increase.（2）In the range of the parameter distance studied this dissertation（S_f/D₀=0.11、0.16、0.21;h_f/D₀=0.34、0.40、0.46;S_T/S_L=1.09、1.00、0.92）.When Re is constant,（?）_m increases with the increase of fin spacing and fin height;Both （?）m and C_dm decrease with the increase of fin spacing,while （?）m and C_dm increase with the increase of fin height.Moreover,the enhancement of heat transfer ability of spiral serrated annular fin is not obvious with the increase of fin height.In practical application,the loss caused by the increase of fin height should be considered.（?） m and （?）m decrease with the increase of longitudinal tube spacing.（3）For the spiral serrated annular finned single tube and spiral serrated annular finned tube bundle considered this dissertation,Karman vortex shedding can be observed on both sides of the finned tube;Their lift coefficient and drag coefficient fluctuate periodically in the form of trigonometric function,and the frequency of drag coefficient is about twice that of lift coefficient;In addition to each vortex shedding period,there is a large period in which the amplitudes of lift coefficient and drag coefficient first increase and then decrease.（4）Karman vortex has an important influence on the heat transfer capacity of fins.The temperature and （?）_local distribution on the finned tube are related to Karman vortex.When the fin spacing increases,the generation of Karman vortex is beneficial to the convection heat transfer of finned tube,while when the fin height increases,the high frequency Karman vortex is not conducive to the heat transfer of the finned tube;When S_T/S_L is less than 10000,the effect of the generation of the finned Karman vortex on the heat transfer capacity of the fin tube bundle is small;When S_T/S_L is more than 10000,the effect of Karman vortex on the heat transfer capacity of fin tube increases.Therefore,the vortex dynamics and heat transfer characteristics of fin tube bundle should be considered comprehensively for the selection of longitudinal tube spacing.