Performance evaluation of Al₂O₃ nanofluid as an enhanced heat transfer fluid

Thermal performance of Al₂O₃ nanoparticles dispersed in water was evaluated experimentally in a fully instrumented circular tube under turbulent flow conditions. Thermophysical properties of Al₂O₃ nanofluids at three different volumetric concentrations (0.38%, 0.81%, and 1.30%) were determined as a function of temperature. Pressure drop and heat transfer experiments were carried out at different volumetric concentrations and inlet fluid temperatures (10°C–30°C). The overall performance of the Al₂O₃ nanofluids was evaluated by considering both their hydraulic and heat transfer characteristics. The experimental results showed that the use of Al₂O₃ nanofluids increases the pressure drop by up to about 13% due to the greater viscosity. In addition, the heat transfer coefficient of nanofluids increased with the volumetric concentration by up to approximately 19% induced by the enhanced thermal conductivity. Furthermore, the experimental results indicated that the nanofluid with a volume fraction of 0.81% at the highest inlet fluid temperature increases the overall performance by up to around 8% and performs better than the other volume fractions. Enhancement in the overall performance increases with increasing inlet fluid temperature because of both the enhanced effective thermal conductivity and the decreased viscosity, which increases the energy exchange and decreases the pressure loss, respectively.