Influence of Aspect Ratio of Rectangular Enclosure and Nanoparticles Volume Fractions on Natural Convection Heat Transfer of Al2O3-Water Nanofluid; A numerical study

In this study, the variation of aspect ratio (height to width) and nanoparticles volume fractions of on natural convection heat transfer of Alumina-water nanofluid in enclosures was investigated. It is supposed that the nanofluid are applied as incompressible fluid and single phase base on water (as basefluid) include Alumina (Al2O3), with volume fraction (concentration) 0 - 4%, under laminar flow. Governing equations were solved numerically by finite volume method (Fluent). Rayleigh number is in the range of 4×105-108 in 2D enclosures with specific aspect ratios (0.6-3.2) and temperature difference. In the present work with due attention to the used models for the viscosity and the nanofluid coefficientof thermal conduction was showed that the Nusselt number of the nanofluid with more concentration, is increasing due to more viscosity and coefficient of thermal conduction rather than pure water. In other words the Nusselt number in every specific aspect ratio, in minimum of concentration equals 0.3% and in maximum of concentration equals 14% would be decreased. In a specific concentration, The Nusselt number was more related with aspect ratio rather than the coefficientof natural convection heat transfer and thermal conduction.