Effect of core-rod diameter on wire coil inserts for heat transfer and friction factor of high-prandtl number magnetic Fe₃O₄nanofluids in a fully developed laminar flow

An experimental analysis was conducted to estimate the heat transfer, friction factor, and thermal performance factor of high-Prandtl number vacuum pump oil-based magnetic Fe3O4 nanofluids flow in a tube with various core-rod inserted wire coil inserts. The experiments were conducted for 0.05 vol.%, 0.2 vol.%, and 0.5 vol.% concentrations and core-rod diameters of 2, 4, and 6 mm and the pitch/diameter ratio of wire coil inserts equal to 1.79, 2.54, 3.24, 2.17, 3.17, 4.05, 2.90, 4.23, and 5.40. The results show that with the use of 0.05 vol.%, 0.2 vol.%, and 0.5 vol.% concentrations of nanofluid, the Nusselt number is increased by 5.75%, 9.43%, and 13.48% at a mass flow rate of 0.208 kg/s. The influence of core-rod diameter and p/d ratio of the wire coil inserts is observed for the Nusselt number enhancement. Using the core-rod diameter of 6 and p/d value of wire coil equal to 1.79, a maximum enhancement of 63.89% with friction factor penalty of 102.5% was observed for 0.5 vol.% concentration of nanofluid at a flow rate of 0.208 kg/s against base fluid data without inserts. The thermal performance factor is enhanced by 22% for all the measured cases compared to the base fluid.