In this paper, experimental investigation on heat transfer and friction characteristics of dual-pipe heat exchanger for single-phase forced convective flow with alternation of clockwise and counterclockwise twisted tape (ACCT tape) and typical twisted tape (TT tape) inserted in the inner tube has been carried out. And effects of different lengths of twisted tapes on heat transfer enhancement were studied through a circular tube using water as testing fluid in turbulent conditions with a range of Reynolds number between 3000 and 9000. In the dual-pipe heat exchanger, hot water was cooled in the inner tube and cold water was as cooling fluid between the inner tube and the outer tube. The results showed that the ACCT tapes performed better on heat transfer enhancement than the typical twisted tapes and the best effect appeared with the full-length (l = 2400 mm) ACCT tape insert in comparison with the twisted tapes of other lengths. The maximum values of PEC (performance evaluation criteria) with the full-length ACCT tape insert reached 1.42 in experimental flowing conditions. Empirical correlations for Nusselt number and friction factors were established and found to fit the experimental data with a deviation within 8%. (C) 2016 Elsevier Ltd. All rights reserved.