Preparation of stable TiO₂-Graphene/Water hybrid nanofluids and development of a new correlation for thermal conductivity

The current study investigated the variation of the thermal conductivity coefficient of TiO₂-Graphene/Water hybrid nanofluid. Hybrid nanofluids were tested at different temperatures (25 to 75 °C) and different volume fractions (0.005 to 0.5%). The dispersion and stability of nanofluids were investigated by employing the dynamic light scattering and Zeta Potential techniques. Measurements of the thermal conductivity coefficient showed that increase in temperature and volume fraction results in enhancement of thermal conductivity of nanofluids. The results indicated that enhancement of thermal conductivity with increase of solid volume fraction is more pronounced at higher temperatures. However, the effect of increase in volume fraction on thermal conductivity was larger than the effect of temperature. Thermal conductivity at volume fraction of 0.5% and temperature of 75 °C was increased by 27.84% compared to the base fluid. Finally, a model was proposed for predicting the thermal conductivity of nanofluids based on the measured data. According to the results, this model has a margin of error of 1.44%, indicating that the results obtained from model calculations are compatible with experimental data.