The aim of this research was to synthesize copper oxide nanoparticles, which were then applied to prepare CuO-water nanofluid, using a spinning disk reactor (SDR). The precursors of copper oxide were first prepared in a continuous mode through a liquid-liquid reaction using copper (II) sulfate pentahydrate and sodium carbonate as reactants. Then, the precursors were calcined up to 500 degrees C to obtain copper oxide nanoparticles. The effects of operating variables, including disk rotation speed, reactant concentration, and liquid flow rate, on the size of the copper oxide nanoparticles were investigated. Smaller copper oxide particles were obtained under lower reactant concentrations and higher disk rotation speeds. The size of the obtained primary particles of copper oxide ranged between 20 and 30 nm observed under a scanning electron microscope as compared to the number mean size of 40-50 nm determined by a particle size analyzer. Finally, a CuO-water nanofluid was prepared for enhancing the thermal conductivity using various CuO contents and surfactant concentrations. (C) 2010 Elsevier B.V. All rights reserved.