Investigation of thermal conductivity and viscosity of ethylene glycol based ZnO nanofluid

Ethylene glycol (EG) based nanofluids containing ZnO nanoparticles were prepared, and the thermal transport properties including thermal conductivity and viscosity were measured. The results show that the thermal conductivity of ZnO-EG nanofluids is independent of setting time from 20 to 360 min. The absolute thermal conductivity increases with temperature for different temperatures ranging from 10 to 60 °C, while the enhanced ratios are almost constant. The thermal conductivity of ZnO-EG nanofluids depends strongly on particle concentration, and it increases nonlinearly with the volume fraction of nanoparticles. The enhanced value of 5.0 vol.% ZnO-EG nanofluid is 26.5%, consistent with the prediction values by the combination of the aggregation mechanism with the Maxwell and Bruggeman models. The facts indicate that there is no magic physics behind nanofluids and the classical theories predict the measurements well. The rheological behaviors of the nanofluids show that ZnO-EG nanofluids with low volume concentrations demonstrate Newtonian behaviors, and for higher volume concentrations nanofluids, the shear-shinning behavior will be observed, because the effective volume fraction of aggregates is much higher than the actual solid volume fraction.