Experimental study on the convective heat transfer of CuO-water nanofluid in a turbulent flow

The turbulent convective heat transfer behavior of nanoparticle dispersions in water with three different particle sizes (23 nm, 51 nm, and 76 nm) is investigated experimentally in a flow loop with a constant heat flux. The main purpose of this study is to evaluate the effect of particle size on convective heat transfer in a turbulent region. The experimental results show that suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid, and the nanofluid with 76-nm particles shows a higher heat transfer coefficient than nanofluids containing the other two particle sizes, especially at a high Reynolds number. The experimental data are compared with the Xuan and Roetzel correlation 2000. Based on the effective medium approximation and the fractal theory, we have obtained the effective thermal conductivity of suspension. It is shown that if the new effective thermal conductivity correlation of nanofluids is used in calculating the Prandtl and Nusselt numbers, the new correlation accurately reproduces the convective heat transfer behavior in tubes.