Convective Heat Transfer and Friction Factor Characteristics in Internally Threaded Tube with Constant Heat Flux for Al2O3/Water Nanofluid

This work presents an experimental study on the mean Nusselt number, friction factor and thermal enhancement factor characteristics in a circular plain tube and internally threaded tube under uniform wall heat flux boundary conditions for pure water and Al2O3 nanofluid as working fluid. The effects of the internal threads and nanofluid on the Nusselt number and the friction factor are determined in a circular tube with a fully developed turbulent flow for the Reynolds number in the range between 3000 and 25000. The horizontal tube with 1200 mm length was used as the test section having internal knuckle threads of pitch 12 mm. Firstly the experiments were performed on plain tube and internally threaded tube with pure water as working fluid and secondly with nanofluid consisted of Al2O3 nanoparticles with an average diameter of 12 nm dispersed in water having volume fraction of 1.5 %. The heat transfer and pressure drop data obtained was compared with the data obtained from a plain tube under similar geometric and flow conditions. It is observed that at all Reynolds number, the Nusselt number and thermal performance increases for a tube with internal threads and nanofluid as compared with plain tube and pure water. These are because of increase in thermal diffusivity of nanofluid and also because of strength and intensity of vortices ejected from the internal threads. Subsequently an empirical correlation is also formulated to match with experimental results with 7 % and 8 %, variation respectively for Nusselt number and friction factor.