One major hurdle in efficient design of electronic devices as they get smaller is to remove the generated heat. In this study, the thermal performance of a cylindrical microchannel heat sink was experimentally investigated for potential cooling of electronic devices. The heat sink comprised of 86 rectangular microchannels with hydraulic diameter of 560 mu m assembled into a cylindrical geometry. A number of thermocouples were embedded along the microchannel to provide local temperature measurements. The Cu-water nanofluid with different concentrations was used as coolant for heat fluxes of 35 and 50 kW/m(2). The Nusselt numbers of nanofluids with 0.05, 0.1 and 0.3 wt% concentration were enhanced approximately 17%, 19% and 23% compared to that of pure water for similar Reynolds numbers. Further increase of Re in laminar flow regime (Re < 900) led to lower Nusselt numbers for the nanofluid. Moreover, the increase of pressure drop versus Re was evaluated. While an appreciable enhancement was obtained for the heat transfer coefficient of 0.3 wt% compared to that of pure water, the corresponding pressure drop was nonetheless less than 0.15 bar. (C) 2015 Elsevier Ltd. All rights reserved.