Viscosity, thermal conductivity and density of carbon quantum dots nanofluids: an experimental investigation and development of new correlation function and ANN modeling

Abstract

This paper reports an experimental investigation on the viscosity, thermal conductivity and density of water, ethylene glycol, and water–ethylene glycol mixture (60:40 vol%)-based carbon quantum dots (CQDs) nanofluids. Stable nanofluids were prepared by two-step technique at room temperature, and the thermophysical properties of them were measured at various temperatures and volume fractions (0.2–1 vol%). The presence of CQDs enhances the viscosity and thermal conductivity of nanofluids noticeably. The maximum thermal conductivity enhancement reaches up to 8.2%, 25.1%, and 13.3% for the nanofluid containing 1% CQDs at 50 °C in ethylene glycol, water, and water–ethylene glycol mixture (60:40) as base fluids, respectively. In addition, the viscosity of each solution was measured, and the results show that it increases with increasing volume fractions of CQDs nanoparticles and decreased with increasing temperature. Additionally, to correlate viscosity, thermal conductivity, and density of nanofluids, some new empirical equations are derived and compared with experimental data and other theoretical models. Besides, three artificial neural network models are applied to predict the viscosity, thermal conductivity, and density of nanofluids and they are in excellent agreement with experimental data with the AAD = 1.29% and R2 = 0.99994 for viscosity, AAD = 0.85% and R2 = 0.99867 for thermal conductivity, and AAD = 0.01% and R2 = 0.99999 for density of nanofluids.