Study of rheological behavior of water-ethylene glycol /nano Al2O3 –nano graphene hybrid nanofluid at low temperatures

Nanofluids are a new generation of fluids with very high potential in industrial applications. In this study, the effect of temperature and concentration of nanoparticles consisting of Al2O3 nanoparticles and graphene nanoplates on the rheological behavior of the base fluid consisting of water and ethylene glycol was studied. Also, 0.2% vol. of oleic acid (OA) and 0.2% wt. 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 in this study was considered 0.05, 0.1, 0.5, 1, 1.5, 2 and 2.5% by volume and also to investigate the effect of temperature, the tested temperatures were selected in the temperature range of 263-293 K. The morphology and microstructure of the nanoparticles were investigated by SEM and TEM. Detection of phases in nanoparticles was performed by XRD analysis. Also, specific area and porosity of nanoparticles were determined by BET analysis. Dynamic viscosity of hybrid nanofluids was measured and compared with the base fluid. The results showed that the rheological properties of water-ethylene glycol/nano graphene-nano alumina hybrid nanofluid were highly dependent on temperature and nanoparticle concentration, especially at sub-zero temperatures. Dynamic viscosity results showed that hybrid nanofluid samples with solid volume fractions less than 0.5% Newtonian behavior, while samples with higher solid volume fractions showed non-Newtonian shear thinning behavior.