Turbulent forced convection effectiveness of alumina-water nanofluid in a circular tube with elevated inlet fluid temperatures: An experimental study

The present study aims to explore experimentally the influence of elevated inlet fluid temperature on the turbulent forced convective heat transfer effectiveness of using alumina-water nanofluid over pure water in an iso-flux heated horizontal circular tube at a fixed heating power. A copper circular pipe of inner diameter 3.4mm was used in the forced convection experiments undertaken for the pertinent parameters in the following ranges: the inlet fluid temperature, T_in=25°C, 37°C and 50°C; the Reynolds number, Re_bf=3000-13,000; the mass fraction of the alumina nanoparticles in the water-based nanofluid formulated, ω_np=0, 2, 5, and 10wt.%; and the heating flux, q_o^″=57.8-63.1kW/m². The experimental results clearly indicate that the turbulent forced convection heat transfer effectiveness of the alumina-water nanofluid over that of the pure water can be further uplifted by elevating its inlet temperature entering the circular tube well above the ambient, thereby manifesting its potential as an effective warm functional coolant. Specifically, an increase in the averaged heat transfer enhancement of more than 44% arises for the nanofluid of ω_np=2wt.% as the inlet fluid temperature is increased from 25°C to 50°C.