| Tube fin heat exchanger has the advantages of compact structure and convenient processing, which is widely used in many fields such as refrigeration, air conditioning,chemical industry, power production and so on. Fin side fluid of the most tube fin heat exchangers is air, due to the large flow coefficient of the fin side, the operation cost of the heat exchanger is increased, so it is a very important task to reduce the flow resistance coefficient of the fin side. Stamping the flow distributors in ball shaped convex before the stagnation point of the tube is one way to reduce flow resistance. When the fluid flows through the fin side channel of tube fin heat exchanger, flow distributors change the streamline and effectively reduce the flow resistance. The numerical method is used to get the fin side channel heat transfer, flow resistance and the mechanical energy dissipation characteristics, and makes a detailed analysis of its mechanism.This article selects the fin side channel of the tube fin heat exchanger with flow distributors in ball shaped convex as computational domain, and the reasonable grid system is generated. In order to guarantee the correctness of the numerical simulation results, the rationality of the grid size is assessed. In order to prove the rationality of the numerical simulation method, the numerical data is compared with experimental data. Then, based on numerical results, various performances are compared under the same size of tube bank fin with flow distributors in the ball shaped convex and the plain fin, these performances mainly include the flow fields and the temperature fields on the transversal and longitudinal sections of the channel, Nusselt number Nu and flow resistance coefficient f changes with Reynolds number Re. The influence of the structural parameters of flow distributors in ball shaped convex, such as fin spacing of Tp, horizontal tube spacing S1, spacing of convex ball S3,convex ball base level axis ratio Bit（the ratio of the long axis and short axis）, deepness c are obtained. The mechanical energy dissipation characteristics of fluid flow in the channel, and the reasons for the formation of the flow resistance characteristics are revealed.The results show that, compared with the plain fin, under the condition of the same structure and working condition, with flow distributors in ball shaped convex fin decreases heat transfer of 2.72%, decreases the flow resistance coefficient of 2.86%, when the Reynolds number is large, flow distributors in ball shaped convex can decrease more the flow resistance coefficient. The heat transfer ability on the bottom surface is stronger than on the top surface.The mechanical energy dissipation φ are mainly distributed in the fin and tube surface, and φare large in the region near the convex ball front surface and in the region near the tube surface with arc angle of 20°-110°（angle starts from the stagnation point）. The local mechanical energy dissipation and the local Nusselt number distribution trend along themainstream direction are consistent. The mechanical energy dissipation of the plain fin channel is larger than that with flow distributors in ball shaped convex fin channel, the flow distributors in ball shaped convex reduce the mechanical energy dissipation of the fin side channel, thus reduce the pressure loss of the fin side channel. Transversal average mechanical energy dissipation and transversal average Nusselt number have a certain correlated relationship. |
