Comparison of experimental and theoretical methods of obtaining the thermal properties of alumina/iron mono and hybrid nanofluids

Abstract

The use of hybrid nanofluids is gaining wide application due to their reported improvement in heat transfer properties rising from the combined thermal properties of two or more nanoparticles. This study presents an experimental investigation into the thermal performance of Al2O3 nanofluids and Al2O3-Fe hybrid nanofluids both using water as the base fluids. The nanoparticles are carefully characterized using Scanning electron microscopy (SEM) and X-ray diffractometric analysis (XRD), while a zeta potential test is conducted to ascertain the stability of the nanofluids. The thermo-physical properties measurements are carried out over 5 temperature ranges from 25 °C–65 °C at three nanoparticle concentration of 0.05%, 0.1%, and 0.2%. To ensure the reliability of the obtained measurements, the thermal properties of pure water was measured and compared with the globally accepted ASHRAE standard. The performance of the experimentally obtained data for both nanofluids was then compared to theoretical models. The results show that the use of the nanofluids led to a reduction in the values of specific heat capacity. The highest mean reduction recorded was 37% which was for the hybrid Al2O3-Fe nanofluids at 0.2% concentration. The use of the hybrid nanofluids showed significant improvements in the thermal conductivity of the base fluid especially at higher values of nanoparticle volumetric concentrations. A 14% mean enhancement in thermal conductivity was recorded at 0.2% concentration for the hybrid nanofluids, while an enhancement of 7.8% and 7.5% were recorded with the use of Al2O3-Fe nanofluids and Al2O3 nanofluids respectively at 0.1% concentrations. For the theoretical models, better correlations are needed that would account for both the interfacial interactions and existence of nanolayers in the fluids. This would aid in making better predictions of the properties of viscosity and specific heat capacities of nanofluids respectively.