Magnetic field dependent thermal conductivity investigation of water based Fe3O4/CNT and Fe3O4/graphene magnetic hybrid nanofluids using a Helmholtz coil system setup

Magnetic hybrid nanofluids are making a name of themselves in mainstream application areas such as heat transfer, solar systems, acoustic applications, etc. These nanofluids are highly favorable as their ability to advance the properties of their constituent particles such as their thermophysical properties. This study aims to investigate the magnetic field dependent thermal conductivity of Fe3O4/CNT – water and Fe3O4/Graphene – water magnetic hybrid nanofluids. The thermal conductivity investigations are carried out with the 3ω method under a uniform magnetic field generated by a 3D Helmholtz coil system. Fe3O4/CNT – water and Fe3O4/Graphene – water magnetic hybrid nanofluids were purchased commercially as 20 wt% colloids. Then, the samples with 1, 2, 3, 4, and 5 wt% were prepared by diluting them with DI water. Thermal conductivity measurements were carried out for the samples under the external uniform magnetic field in the range of 0–250 G in both parallel and perpendicular directions to the temperature gradient generated by the thermal conductivity measurement probe. The results pointed out that the thermal conductivity of the samples increases as the magnetic field and particle concentration increase for both magnetic hybrid nanofluids. Additionally, it is obtained that the thermal conductivity enhancement of Fe3O4/Graphene – water is up to 3 times higher than Fe3O4/CNT – water samples. Moreover, the maximum thermal conductivity enhancement was observed as ∼12 % and ∼9 % for Fe3O4/CNT – water, and ∼51 % and ∼21 % Fe3O4/Graphene – water under external magnetic field application with parallel and perpendicular direction, respectively.