An experimental study was carried out to examine the heat transfer enhancement a circular straight tube by using the Cu-water nanofluid flow and different inserts. The investigated parameters were (1) three concentrations of Cu nanoparticles: 0.0%, 0.1%, and 0.3% by volume (2) six different shapes of inserts: perforated-tape, jagged-tape, twisted-tape, helical-screw, vortex-generator, and offset-strip (3) seven volumetric flow rates: 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0l/min. Test results indicated that the thermal-hydraulic performance of the tube was strongly related to the shape of inserts. It was found that the tube fitted with the vortex-generator insert offered the highest values of the heat transfer coefficient and pressure drop. It was also detected that the best thermal-hydraulic performance compared to the empty tube was obtained by the vortex-generator insert and followed by the twisted-tape and jagged-tape inserts. Over the tested range of the flow rate, the considered performance evaluation criterion of the jagged-tape, twisted-tape, helical-screw, vortex-generator, and offset-strip inserts averagely increased, respectively, by about 76.9%, 100.1%, 55.3%, 228.5%, and 8.4% compared to that of the empty tube. Furthermore, the use of nanofluid had more benefit at the higher flow rates and high nanoparticle weight fractions. (C) 2015 Elsevier B.V. All rights reserved.