Laminar mixed convection of TiO2-water nanofluid in horizontal uniformly heated pipe flow

Laminar flow experiments in a uniformly heated pipe are carried out over a large range of parameters. As long as free convection is negligible, nanofluid Nusselt number development along the pipe axis is well described by analytical solutions. However, the onset of free convection is delayed. The following development of the Nusselt number departs significantly from the equivalent water values. Moreover, enhancement of heat transfer due to additional free convection is in general much weaker in nanofluid flow than in single-phase flow. The found deterioration is attributed to the movement nanoparticles due to Brownian and thermophoretic diffusion.