Reduced Graphene Oxide-Fe₃O₄ Nanocomposite Based Nanofluids: Study on Ultrasonic Assisted Synthesis, Thermal Conductivity, Rheology, and Convective Heat Transfer

The present work deals with the preparation of reduced graphene oxide-Fe 3 O 4 (rGO-Fe 3 O 4 ) nanocomposite and its nanofluid by an ultrasound assisted method for convective heat transfer study. Formation of the rGO-Fe 3 O 4 nanocomposite with a uniform distribution of smaller sized (10–20 nm) Fe 3 O 4 nanoparticles on graphene nanosheets was confirmed from UV/vis, transmission electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron spectroscopy analysis. Thermal conductivity of prepared rGO-Fe 3 O 4 nanocomposite based nanofluids with the aid of ultrasound showed an 83.44% enhancement for 0.2 vol % concentration of the rGO-Fe 3 O 4 nanocomposite at 40 °C. Rheological study revealed non-Newtonian behavior of the nanofluids. Various viscosity models were used to predict the behavior of rGO-Fe 3 O 4 nanocomposite based nanofluids. The estimated heat transfer coefficient with the use of 0.02 vol % rGO-Fe 3 O 4 nanofluid at the exit of the test section was 4289.5 W/m 2 ·K for the Reynolds number equal to 7510 ± 5. A new correlation for the estimation of Nusselt number has been proposed for the rGO-Fe 3 O 4 nanofluid which fits the experimental data very well.