Simulação numérica da convecção natural em cavidade porosa bi-dispersa aquecida por baixo

Abstract

In this work it is investigated the transport phenomenon by heat transfer through natural convection in a bi-disperse square cavity heated from below. The cavity is represented by porous, square, disconnected blocks uniformly distributed. The numerical simulation of the bi-disperse medium is done by solving the balance equations of mass, momentum and energy for the fluid phase (Navier-Stokes) and for the porous phase of the blocks (Darcy-Brinkman-Forchheimer). The algorithm used for the pressure-velocity coupling is the SIMPLEC and the interpolation scheme for the convective terms is the QUICK. Results are presented for the variation of the Rayleigh number ( Ra  105 - 10 7 ), the Darcy number ( Da  104 - 108 ), the internal porosity of the blocks (I  0, 4 - 0, 6 ) and the number of blocks ( N  1; 4;16;36; 64 ). The heat transfer through the medium is evaluated quantitatively by the Nusselt number on the lower surface of the cavity, and qualitatively by the isothermals and streamlines. Raising the Rayleigh number, it is observed an intensification on the recirculation of fluid inside the cavity and, consequently, an increase on the heat transfer. Likewise, with an increase on the Darcy number, it is verified an increase on the internal permeability of the blocks, enhancing the whole recirculation inside the cavity. The variation on the internal porosity of the blocks presents low influence when compared to the other parameters. Generally, the increase on the number of blocks reduces the external permeability of the cavity, intensifying the resistance to the fluid flow, propitiating the horizontal stratification of the isothermals. For certain configurations ( Ra, Da, I , N ), the horizontal stratification is characterized for the regime of pure conduction.