Experimental investigation of thermal conductivity and viscosity of ethylene glycol based ZnO nanofluids

In this work, well dispersed ethylene glycol (EG) based nanofluids containing ZnO nanoparticles with different mass fractions between 1.75% and 10.5% were prepared by a typical two-step method. Structural properties of the dry ZnO nanoparticles were measured with X-ray diffraction（XRD）and Transmission Electron Microscopy (TEM). Thermal transport properties including thermal conductivity and viscosity were experimentally measured for the nanofluids. The experimental results show that thermal conductivity increases slightly with increasing the temperature from 15 to 55 °C. It depends strongly on particle concentration and increases nonlinearly with the concentration within the range studied. The enhanced value is higher than the value predicted by the Hamilton and Crosser (H–C) model. Moreover, viscosity increases with concentration as usual for ZnO nanoparticles and decreases with temperature. For an analysis of the rheological behaviors, it shows that ZnO-EG nanofluids with mass fraction wt.% ≤ 10.5 demonstrate Newtonian behaviors.