The influences of twisted-leaf piech Lp

swirl angle β and twist angle α on the characteristics of heat transfer and flow resistance of plain circular tube with inserted twisted-leaves discontinuously for air turbulent flow were analyzed in detail by numerical simulation and the optimized structure of the twisted-leaves was obtained based on heat transfer enhancement valuation factor η.In addition

the numerical simulation predictions were verified by experiment.The results indicated that the larger the α

the better the performance of heat transfer and the greater the flow resistance; the larger the Lp

the worse the performance of heat transfer and the smaller the flow resistance; the larger the β

the better performance of heat transfer while the variation of flow resistance was not monotone because of the combined control of friction resistance and shape drag.The optimized structure parameters of twisted-leaf were swirl angle β=20.3°

twist angle α=180°

twisted-leaf pitch Lp=33d（d means the width of twisted-leaf）.Furthermore

compared with twist angle α

the influence of swirl angle β on heat transfer enhancement was much stronger.