The characteristics of heat transfer and flow resistance on the air side in a finned circular-tube air-cooler with a pair of oblique-cut semi-elliptic cylinder shells or delta winglets behind circular-tubes were investigated numerically.In-line and staggered arrangements of two rows of circular-tubes in the air cooler were considered

separately.The Reynolds number of the air flow ranged from 400 to 2200.The heat transfer enhancement and flow resistance of these two vortex generators were compared by using the comprehensive performance factor R=(j/j0)/(f/f0).The results show that the two vortex generators have almost the same heat transfer enhancement performance.However

due to the streamlined design of oblique-cut semi-elliptic cylinder shells

the corresponding flow resistances in the air coolers with in-line and staggered tubes are 0.07%—2.53% and 1.51%—5.31% lower than those of delta winglets

respectively.The two vortex generators have better effect on flow resistance reduction in the air cooler with staggered tubes at higher Reynolds numbers.The reduction of oblique-cut semi-elliptic cylinder shells is 6.40% at most and that of delta winglets is 4.39%.The R value of oblique-cut semi-elliptic cylinder shells is 0.68%—4.36% higher than that of delta winglets in the air cooler with in-line tubes for Re>700

and it is 0.79%—4.78% higher in the air cooler with staggered tubes.Moreover

the R value of oblique-cut semi-elliptic cylinder shells in the air cooler with staggered tubes is 3.11%—28.38% higher than that with in-line tubes.