Thermal and Flow Properties of Graphene/Fe3O4 Water-Based Hybrid Nanofluids

Carbon-iron oxide nanoparticles represent a promising class of hybrid nanomaterials for the development of nanofluids aimed at enhancing heat transfer in thermal systems. This study presents a comprehensive investigation into the thermal conductivity (k), specific heat capacity at constant pressure (C_p), rheological behavior and viscosity (μ) of graphene: Fe₃O₄ (mass ratio of 70:30) dispersions in distilled water, stabilized using a surfactant mixture of karaya gum and cocoamidopropyl betaine. Experimental results were thoughtfully analyzed to elucidate the effects that surfactant mixture’s presence, hybrid nanoparticle’s concentration (0.005–0.100 wt.%) and temperature (283.15–313.15 K) may have on the three thermophysical properties under study. Findings highlight that, while the used surfactant content exerts a negligible influence on thermal conductivity, the addition of graphene-Fe₃O₄ nanoparticles leads to a marked improvement in k, reaching up to a 6% enhancement at a mass concentration of 0.1 wt.%. Modest reductions were observed in the isobaric heat capacity, 0.3–2.4% in the investigated concentration range. Rheological studies showed a transition from the Newtonian behavior of 0.005 and 0.010 wt.% samples to the shear-thinning of 0.025–0.100 wt.%. Finally, results are compared to some theoretical correlations, novel regression models are proposed to describe the temperature and concentration dependence of nanofluid thermal conductivity and viscosity.