The overheating of mechanical and electrical components in generators of wind turbines considerably reduces their overall performance. Consequently, their cooling systems usually need to dissipate large amounts of heat, leading to high electrical energy consumptions. These systems habitually use commercial industrial coolants as working fluids in order to avoid freezing at low temperatures and corrosion of mechanisms. Dispersions of graphene nanoplatelets are expected to enhance the thermal conductivity of glycolated water-based fluids, but scarce studies were reported in the literature using commercial industrial antifreezes as base fluid. In this study a comprehensive thermophysical characterization of different loaded polycarboxylate chemically modified graphene nanoplatelet nanofluids (0.25, 0.50, 0.75 and 1.0 wt.%) based on a commercial coolant, Havoline ® XLC Premixed 50/50, extensively employed in cooling systems of wind turbines, was carried out. Firstly, with the purpose of achieving long-term stabilities, it was found the optimum sodium dodecyl benzene sulphonate concentration, 0.125 wt.%, through zeta potential and dynamic light scattering measurements, finding no substantial alteration of the original pH value. Densities were measured by pycnometry, heat capacities by differential scanning calorimetry and thermal conductivities by transient hot wire technique, in the temperature range from 293.15 to 343.15 K. Moreover, rheological behaviour was experimentally determined by means of a rotational rheometer with cone-plate geometry at temperatures from 293.15 to 323.15 K. Thermal conductivity enhancements reaching 7.3 % and dynamic viscosity increases up to 20 % were found. Potential heat transfer performance capabilities and pumping power consumptions in both laminar and turbulent flow conditions were investigated through the analysis of equivalent ratios derived from the experimentally measured properties, optimal concentrations for both regimes being determined.

Convection heat transfer coefficients and pressure drops of four functionalized graphene nanoplatelet nanofluids based on the commercial coolant Havoline® XLC Pre-mixed 50/50 were experimentally determined to assess its thermal performance. The potential heat transfer enhancement produced by nanofluids could play an important role in increasing the efficiency of cooling systems. Particularly in wind power, the increasing size of the wind turbines, up to 10 MW nowadays, requires sophisticated liquid cooling systems to keep the nominal temperature conditions and protect the components from temperature degradation and hazardous environment in off-shore wind parks. The effect of nanoadditive loading, temperature and Reynolds number in convection heat transfer coefficients and pressure drops is discussed. A dimensionless analysis of the results is carried out and empirical correlations for the Nusselt number and Darcy friction factor are proposed. A maximum enhancement in the convection heat transfer coefficient of 7% was found for the nanofluid with nanoadditive loading of 0.25 wt %. Contrarily, no enhancement was found for the nanofluids of higher functionalized graphene nanoplatelet mass fraction.