Abstract
The heat transfer coefficient and friction factor of Fe3O4/vacuum pump oil nanofluids flowing in a tube with twisted tape inserts were analyzed experimentally. The experiments were conducted for different mass flow rates (0.04 kg/s to 0.208 kg/s), volume concentrations (0.05% to 0.5%), Prandtl numbers (440 to 2534), Graetz numbers (500 to 3000) and twisted tape inserts (H/D = 5, 10 and 15). Results reveal that the Nusselt number is enhanced by 8.94% and 13.48% for the 0.5% nanofluid for the mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, relative to the base fluid. For the mass flow rate of 0.208 kg/s with 0.5 vol. % nanofluid, the friction factor penalty is 1.21-times compared to the base fluid. By using twisted tape insert of H/D = 5, the Nusselt number is further enhanced by 23.86% and 39.53% for the 0.5% nanofluid for mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, relative to the base fluid. For the twisted tape insert of H/D = 5 with mass flow rate of 0.208 kg/s and 0.5 vol. % nanofluid, the friction factor penalty is 1.44-times compared to the base fluid. New Nusselt number and friction factor correlations are proposed.