Numerical Study On Fluid Flow And Heat Transfer In The Channel Of Annular Finned Tube

As one of the important heat exchange equipment, the heat exchanger has great influence on the economy, reliability and efficiency of the thermal system.Annular finned tube is widely used in air conditioning, electric power, chemical and other industries because of its high thermal efficiency and compact structure,which has been the attention of many experts and scholars. Scholars focused on increasing the heat transfer at the same time reducing the resistance loss. In order to research the annular finned tube with high efficiency, compactness and low resistance, we must fully understand channel internal complex flow field and temperature field in details, reveal the flow characteristics, analysis the reason why the resistance loss generates and how heat transfer mechanism is enhanced. Therefore, we obtain air velocity, temperature,pressure outside the annular fin tube, temperature and nusselt number distribution on the surface of fin by means of numerical simulation,shape factor, the structural parameters, and the flow parameters of annular finned tube are researched about heat transfer,resistance loss, the comprehensive heat transfer, fin efficiency and heat dissipation of annular fin tube.In this paper, the numerical simulation of fluid flow and heat transfer in an annular finned tube channel is carried out by using Fluent numerical simulation software. First of all, under the condition of the same dimension of the base tube,5 kinds of elliptical fins respectively have same fin minimum cross-sectional area(A_min), fin area(A_fin), fin equivalent diameter（D_e）, fin perimeter(P_er) and fin ratio（β） with circular finned tube(C_ir), 6 kinds of annular finned tubes have been compared for heat transfer, pressure drop, fin efficiency and heat dissipation.Secondly, when the annular fins are equal in area, the influence of the change of the fin shape factor on air velocity and pressure distribution between the annular finned tube is studied. In addition, when the size of the annular fin and the base tube is constant, the change of tube position and arrangement of tube bundle heat exchanger are researched for heat transfer, resistance loss, comprehensive heat transfer, fin efficiency, heat dissipation, which provides important theoretical guidance.The study shows: Among 6 annular fin tubes that are researched, the back-flow area of finned tube Amin is smallest and its heat transfer is best, which is suitable for higher heat transfer requirements. The resistance coefficient and power consumption of Elliptical f_in tube A_fin, P_er, β is lower than the circular fin,but the fin efficiency of elliptical fin tubes is higher. Under the same structural parameters, with the increase of the fin shape factor, the heat transfer performance of the annular finned tube is decreased, the resistance coefficient is reduced, and the comprehensive heat transfer is reduced. When the velocity of air inlet is constant, there is the best shape factor, so that the maximum value of the annular fin efficiency can be achieved. When the shape parameters of the annular fin tube are constant, with the base tube backward bias, windward fin surface area increases, while the leeward surface area decreases, which reduces the influence of the inverse flow zone, and comprehensive heat transfer performance gradually is improved, increasing the amount of heat dissipation;the heat transfer performance is gradually increased, the heat transfer is increased, and the optimum base tube position is existed for the maximum fin efficiency. Staggered annular finned tube bundle arrangement increases thechange of turbulence in the fluid between the annular fin tube bundles, reduces the tube wake region. A large whirlpool area is formed after the in-line annular fin tube. As a result, the comprehensive heat transfer performance of the staggered annular fin tube bundles is better, but the fin efficiency of the staggered annular fin tube bundles is relatively lower.