In order to study the heat transfer and flow characteristics of fluid flowing through the built-in twisted belt external thread tubes, in the Reynolds number range of 2000-12,000, the heat transfer and flow characteristics were studied respectively for the Cu, Al, Al2O3, Fe2O3, multiwalled carbon, and Graphite nanofluids with the mass fraction of 0.1-0.6%. The results show that the Cu nanofluids has the best convective heat transfer effect among numerous nanofluids, and the heat transfer characteristics reach the optimum when the mass fraction of Cu nanofluids is 0.5%. The heat transfer performance of built-in twisted belt external thread tubes increased 50.32% compared to the horizontal tube, indicating that built-in twisted belt external thread tubes has the ability to strengthen heat transfer. With the decrease of the pitch, the heat transfer coefficient and flow resistance were both increased. According to the experimental data, the comprehensive analysis of hot performance coefficient was carried out and the correlation of convective heat transfer and flow resistance in the built-in twisted belt external thread tubes was obtained. (C) 2016 Elsevier Ltd. All rights reserved.