Thermophysical profile of ethylene glycol-based ZnO nanofluids

• Newtonian behaviour has been reported for ZnO–EG nanofluids.
• Thermal conductivity increases nonlinearly with temperature.
• The high pressure volumetric trend of the nanofluid is shown to be non ideal.

This work presents values of the experimental thermal conductivity, viscosity and density of homogeneous and stable nanofluids consisting of both synthesized and commercial ZnO nanoparticles dispersed in ethylene glycol (EG). The influence of variables such as particle size, temperature and volume fraction on their thermophysical properties were studied at concentrations up to 6.2%. The experimental results provide the evidence that thermal conductivity increases non-linearly with concentration and temperature within the range studied. Viscosity increases with concentration as usual for this type of dispersion and decreases with temperature. Density as a function of pressure has been also examined. The mixing volumes show little dependence on temperature and pressure over the range studied. Nevertheless, these results show a contractive behaviour on mixing and a departure from ideal behaviour, and this effect increases with concentration. The influence of particle size is significant for the measured properties, especially on viscosity. Finally, experimental values of thermal conductivity and viscosity have been compared to estimations provided by several simple theoretical models.