Functionalized graphene nanoplatelet nanofluids based on a commercial industrial antifreeze for the thermal performance enhancement of wind turbines

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 (R) 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, theological 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.