MHD Natural convection around a permeable triangular cylinder inside a square enclosure filled with Al 2 O 3 −H 2 O nanofluid: An LBM study

Abstract

Natural convection heat transfer between a hot triangular-shaped permeable cylinder and a cold square enclosure is examined under the influence of magnetic field using lattice Boltzmann method. The effects of Rayleigh number (Ra), Darcy number (Da), Hartmann number (Ha) and orientation of the permeable body are critically investigated on the hydrothermal characteristics. Al 2 O 3 -water nanofluid with 5% volume fraction is considered as a working fluid, and the results are compared with pure fluid. In order to capture porous characteristics, a force term which has the effects of linear and nonlinear drag forces of the porous medium (the Darcy-Forchheimer term) is coupled with BGK-collision operator. The ranges of Rayleigh number and Darcy number considered in the study are 10 4 ≤ Ra ≤ 10 6 and 10 −6 ≤Da≤10 −2 , respectively. Obtained results are delineated in the form of streamlines, velocity profiles, isotherms and local, surface and mean Nusselt number for Ha = 0, 25 and 50. It is seen that the permeability increment enhances the fluid momentum, whereas the magnetic field reduces the kinetic energy of the fluid. Furthermore, the effect of Darcy number and Hartmann number on heat transfer of apex-facing up configuration is higher than that of apex-facing down case. Moreover, the increment in Ha suppresses the intensity of permeability on heat transfer enhancement. The Mean Nusselt number values of apex-facing up triangular configuration are reported to be higher than that of apex-facing down configuration for all values of Ra, Da and Ha embraced in this study. © 2019 Elsevier Ltd