Model-Based Prediction and Comparative Analysis of Density and Specific Heat Capacity of CuO and Graphene Oxide Nanofluids in Water–Ethylene Glycol

Abstract

Density and specific heat capacity are two very important thermo-physical properties used in evaluating the suitability of nanofluids for heat transfer and thermal management applications. In the present study, a model-driven comparative evaluation of copper oxide (CuO) and graphene oxide (GO) nanofluids suspended in a 60:40 by-volume water–ethylene glycol (W–EG) base fluid is proposed. The calculations were performed for the nanoparticle volume concentrations 0.05, 0.10, 0.25 and 0.50 % in the temperature range 25–55 °C. The density of W–EG base fluid was calculated from the temperature-dependent densities of water and ethylene glycol and the nanofluid density was calculated by a volume-fraction mixture relation. The specific heat capacity was calculated by a thermal-equilibrium, density-weighted mixture equation using the specific heat capacities and densities of base fluid and nanoparticles. The results show that the density decreases with increasing temperature and increases with increasing nanoparticle concentration and that the specific heat capacity increases with increasing temperature and decreases with increasing nanoparticle concentration. The density penalty of CuO is higher than that of GO because of its better density. About 2.51% and 0.38% density augmentation over base fluid at 0.5 vol% and 55 °C are predicted for CuO/W-EG and GO/W-EG respectively. For the same conditions, the calculated specific heat reduction is about 2.55% for CuO/W–EG and 0.70% for GO/W–EG. The trends are in good agreement with the experimental research carried out for GO/W–EG and CuO nanofluids, and also with the recent researches that emphasize the need for models that consider the variation of temperature and concentration. The values for current density and specific heat are theoretical and not experimental, so comparisons to the literature are to validate trends/models rather than claim a direct numerical concordance. Results show that the density penalty is lower and the base-fluid specific heat capacity is less compromised for GO/W-EG than for CuO/W-EG under the studied conditions.