Simulation of nanofluid natural convection in a U-shaped cavity equipped by a heating obstacle: Effect of cavity's aspect ratio

Research on nanofluid for heat transfer enhancement of thermal systems has received great attention owing to the lack of energy sources. In this study, fluid flow and natural convection heat transfer of Al2O3 Water or TiO2-water nanofluid inside a U-shaped cavity consist of a hot obstacle has been investigated numerically by lattice Boltzmann method (LBM). In this paper, different parameters are investigated such as Rayleigh number, the solid volume fraction of the nanoparticles, the U-shaped cavity's aspect ratio and heating obstacle's height on the flow field and heat transfer in the enclosure. The results showed that the Rayleigh number (Ra), cavity aspect ratio (AR) and obstacle's height can be affected on isotherms, streamlines and local and average Nusselt number. The average Nusselt number of the obstacle sides increased by increasing the Ra number and solid volume fraction of nanoparticles (phi) regardless the AR. In addition, by increasing the AR, the average Nusselt number increased. At low Ra, the effect of nanoparticles on increment of heat transfer for narrow cavities was more than wide ones. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.