This article presents an experimental evaluation of the thermal-hydraulic performance of carbon nanotube (CNT) nanoparticles dispersed in distilled water in single-phase flow in a horizontal tube. An experimental bench was constructed to evaluate the convective heat transfer coefficient during flow in the transition and turbulent regimes and determine the pressure drop in the flow. The tests were performed while maintaining constant input temperatures in the section of 10, 15, and 20 degrees C, where the heat flux varied between 10 and 18 kW/m(2) and the mass flow rate varied between 20 and 100 g/s. The nanofluids with the multi-walled carbon nanotubes (MWCNTs) in water were tested at volume concentrations that varied between 0.12% and 0.24% with distinct aspect ratios, length by diameter, of 100, 600, and 2400. The experimental heat transfer results were evaluated as a function of mass velocity, G, and Reynolds number, where differences in the behavior were observed. Regarding the pressure drop, the nanofluids exhibited pressure drops between 5% and 8.7% greater than that of the base fluid. Finally, a parameter was proposed to evaluate the obtained results, which relates the increase in heat transfer as a function of pumping power. (C) 2015 Elsevier Ltd. All rights reserved.