Investigation of the effect of temperature and concentration of ceramic nanoparticles on the thermal conductivity of water-ethylene glycol / nano Alumina-nano Graphen hybrid nanofluid

Nanofluid is a suspension obtained by adding nanoscale particles (100 nm) to a base fluid to improve heat transfer. In this study, the effect of temperature and concentration of nanoparticles consisting of Alumina nanoparticles and Graphene nanosheets on the thermal conductivity of a base fluid consisting of water and ethylene glycol was studied. Also, 0.2% by volume of oleic acid (OA) and 0.2% by weight of sodium dodecyl sulfonate (SDS) were added to the base fluid as a surfactant to stabilize and disperse the nanoparticles. The volume fraction of nanoparticles of 0.05, 0.1, 0.5, 1, 1.5, 2 and 2.5% by volume and the tested temperatures were selected in the temperature range of 260-305 K. The morphology and microstructure of the nanoparticles were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermal conductivity of hybrid nanofluids was measured and compared with the base fluid. Results showed that thermal conductivity of water-ethylene glycol / nano Graphene-nano Alumina hybrid nanofluid depends on nanoparticle concentration and temperature. The thermal conductivity measurements of water-ethylene glycol / nano Graphene-nano Alumina hybrid nanofluid were compared with the thermal conductivity prediction models of nanofluids but there was no acceptable agreement. The results showed that increasing the temperature and volumetric concentration of nanoparticles increases the thermal conductivity of hybrid nanofluids. The maximum increase in thermal conductivity of hybrid nanofluid was 44.02% which was obtained in solid volume fraction of 2.5% and at temperature of 303 K.