NUMERICAL SIMULATION ON TURBULENT FLUID FLOW AND HEAT TRANSFER ENHANCEMENT OF A TUBE BANK FIN HEAT EXCHANGER WITH MOUNTED VORTEX GENERATORS ON THE FINS

摘要

Three-dimensional turbulent flow and heat transfer enhancement in the channel formed by staggered tube bank fin heat exchangers with vortex generators (VGs) were studied using a numerical method. Numerical calculations were performed in the range of Reynolds number from 3000 to 20,000. The average Nusselt number and the corresponding friction factor obtained from the numerical study were compared with those obtained from naphthalene sublimation heat/mass analogy experiments in order to validate the numerical method. It was found that the average Nusselt number for the four-row tube bank fin channel mounted with VGs increased by 30.9-47.7% over its counterpart without VGs, and the corresponding friction factor increased by 56.0-66.3%. The local Nusselt number distribution reveals that when VGs are mounted on one fin surface, they can efficiently enhance the heat transfer in the region behind the tube on both fin surfaces. The average Nusselt number increases with increasing the angle of attack 9. However, if the angle of attack is too large, the vortex may break down and decrease heat transfer enhancement. The optimum attack angle for heat transfer augmentation is about θ = 45 deg. Both the average Nu and friction factor decrease with an increase in the tube row numbers. When the Reynolds number is less than 9000, two tube rows are recommended, and when the Re is higher than 9000, the number of tube rows has a small effect on heat transfer performance.