Abstract
An experimental and numerical study was performed to investigate the effect of different formulas for nanofluid thermal conductivity and dynamic viscosity on natural convective heat transfer. It was found that the heat transfer across the enclosure using different models can be enhanced or deteriorated with respect to the base fluid. Also, it was found that the inconsistencies in the reported thermal conductivity and dynamic viscosity from different research groups are mainly due to the characterization of the nanofluid, including determination of colloidal stability and particle size, (i.e., aggregates size) within nanofluid.