3D NUMERICAL ANALYSIS ON FLOW CONFIGURATIONS AND HEAT TRANSFER CHARACTERISTICS FOR FIN-AND-OVAL-TUBE HEAT EXCHANGER WITH V-DOWNSTREAM DELTA WINGLET VORTEX GENERATORS

摘要

3D numerical investigations for heat transfer characteristics and flow configurations in a fin–and-oval-tube heat exchanger with V-tip pointing downstream delta winglet pairs (DDWP) are examined. The DDWPs are placed on the fin surface with pointing downstream and the oval tube row number is set at three in a staggered arrangement. The flow attack angles (α = 15o, 30o, 45o and 60o) and the distance from V-tip to the oval tube center in transverse axis (a = 3.77, 4.77 and 5.77 mm) are investigated for Reynolds number based on hydraulic diameter, Re = 500 – 2500. The numerical results are compared with the previous experimental results and the validations of the grid system on both heat transfer and friction factor are also reported. As the results, it is found that the use of the DDWP performs higher heat transfer rate and the friction factor over than the smooth fin with no DDWP for all cases. The vortex flows and the impinging jet of the flows over the oval-tube walls lead to the increase in heat transfer rate, but also increase in pressure loss. The augmentations are maximum around 1.59 and 4.4 times higher than the smooth fin for heat transfer and friction factor, respectively. In addition, the optimum thermal enhancement factor, TEF is around 1.09 at Re = 2500, a = 5.77 mm and α = 15o.