This study reports the effect of a curved cross sectional twisted tape in a circular tube on heat transfer enhancement by using ANSYS FLUENT v18. Six kinds of inserts having three curve ratios (1.761, 2.252 and 3.271) and two twist ratios (3 and 4) were used over a range of the Reynolds number between about 5800 and 31000. Air was used as a working fluid. Uniform heat flux was applied on the tube wall. The results of heat transfer, friction factor and performance evaluation criteria (PEC) were compared with smooth pipe. Heat transfer and pressure drop of the curved cross sectional twisted tape inserts were higher than the smooth pipe. Nusselt number of the curved cross sectional twisted tape was higher than the smooth pipe in the range of 31 to 89%. The friction factor was higher than the smooth pipe in the range of 122 to 206%. The range of PEC was determined to be between 1.001 and 1.305. The best PEC was calculated as 1.305 at Reynolds number of 5848 for the maximum curve and minimum twist ratio. The correlations of Nusselt number, friction factor, and PEC of the curved cross sectional twisted tapes are presented.