Nanofluids are colloidal solutions which contain a small volume fraction of suspended submicron particles or fibers in heat transfer liquids, such as water or glycol mixtures. Compared with the base fluid, numerous experiments have generally indicated an increase in effective thermal conductivity and a strong temperature dependence of the static effective thermal conductivity. However, in practical applications, a heat conduction mechanism may not be sufficient for cooling high-heat-dissipation devices such as microelectronics or powerful optical equipment. Thus, the thermal performance under convective heat transfer conditions becomes our main task. We report here the heat transfer coefficient in both developing and fully-developed regions by using water-based alumina nanofluids. Our experimental test section consists of a single 1.02-mm-diameter stainless steel tube, which is electrically heated to provide a constant wall heat flux. Both pressure drop and temperature differences are measured. The characterization of nanofluids such as pH, electrical conductivity, particle sizing and zeta potential are also documented. Based on these results, the analysis and applicability of convective heat sinks containing nanofluids are evaluated for contemporary uses.