Experimental study of mixed convection with water–Al2O3 nanofluid in inclined tube with uniform wall heat flux

An experimental investigation was carried out to study mixed convection of Al2O3–water nanofluid inside an inclined copper tube submitted to a uniform wall heat flux at its outer surface. The effects of nanoparticles concentration and power supply on the development of the thermal field are studied and discussed under laminar flow condition. Results show that the experimental heat transfer coefficient decreases slightly with an increase of particle volume concentration from 0 to 4%. Two new correlations are proposed to calculate the Nusselt number in the fully developed region for horizontal and vertical tubes, for Rayleigh number from 5 × 105 to 9.6 × 105, Reynolds number from 350 to 900 and particle volume concentrations up to 4%.