Thermal conductivity of aqueous Al2O3/Ag hybrid nanofluid at different temperatures and volume concentrations: An experimental investigation and development of new correlation function

Nanofluids are a new group of materials with potentially broad applications in the industry, especially in the process of heat transfer. Recently, a new class of nanofluids called hybrid nanofluids are being used to enhance the heat transfer rate. In the present study, an experimental investigation on heat transfer characteristics of aqueous Al2O3/Ag hybrid nanofluids is presented. The main idea in producing hybrid nanofluids was to obtain better heat transfer rate compared to nanofluids dispersed with either of the dispersoids. The detailed surface properties of Ag and Al2O3 nanoparticles were performed by X-ray diffraction and transmission electron microscopy. Polyvinylpyrrolidone used to stabilize the nanoparticles (Al2O3/Ag) in water. Dynamic light scattering and zetapotential measurements measured the particle size distribution of the nanoparticles in the nanofluid and the surface charge formed on the surface of the nanopartide by the polyvinylpyrrolidone. The hybrid nanofluid was prepared by dispersing Al2O3/Ag (50.50) in distilled water, and the thermal conductivity measurements were conducted for particle loading varying from 0.005 vol% to 0.1 vol% using transient hot-wire method. The results indicate that Al2O3/Ag hybrid nanofluids exhibit higher thermal conductivity enhancement compared to Al2O3 nanofluids alone. Based on the experimental data, a new correlation for predicting the thermal conductivity of aqueous Al2O3/Ag has been proposed. (C) 2018 Elsevier B.V. All rights reserved.