Natural convective heat transfer characteristics of Rayleigh-Benard convection of Al<sub>2</sub>O<sub>3</sub>-water nanofluids

Abstract

Transient three-dimensional numerical computations are implemented to clarify the natural convective heat transfer characteristics of the Rayleigh-Benard convection of Al2O3-water nanofluids induced in a shallow vertical cylindrical enclosure. The thermophysical properties of nanofluids, assumed to be a single-phase fluid in the numerical computations, are estimated using the experimental correlation equations reported by Khanafer and Vafai (2011). When the average Nusselt numbers of nanofluids are plotted against the Rayleigh number defined by the thermophysical properties of water, computations for four different volume fractions of nanoparticles were below the average Nusselt number curve experimentally reported by Silveston (1958). The diagram also reveals that the increase of nanoparticles in the base fluid delays the generation of Rayleigh-Benard convection. However, the average Nusselt numbers of nanofluids almost agreed with the average Nusselt numbers of Silveston without depending on the volume fraction of nanoparticles when plotted against the Rayleigh number defined by the thermophysical properties of nanofluids. Thus, the natural convection heat transfer rates of Al2O3-water nanofluids can be considered to be similar to the general fluids reported by Silveston as long as experimental thermophysical properties are employed.