The convective heat transfer characteristics of Al2O3/water and CNT/water nanofluids through uniformly heated horizontal circular tube in transition regime with helical twisted tape inserts are estimated experimentally. Tests were performed with varied range of particle volume concentration (0.15%, 0.45%, 0.60% and 1%) and helical tape inserts of twist ratio (TR) = 1.5, 2.5 and 3. It is observed that the heat transfer performance of both the nanofluids increases with the increase in the particle volume fraction. The CNT/water nanofluids with helical screw tape inserts exhibits higher thermal performance compared to Al2O3/water nanofluid. The maximum enhancement in heat transfer was obtained by using CNT/water nanofluid (phi = 1%) with helical tape inserts of twist ratio 1.5. For all the twist ratio of helical screw tape inserts the pressure drop for Al2O3 nanofluid with helical screw tape inserts is higher compared to the CNT nanofluid. (C) 2014 Elsevier B.V. All rights reserved.