Effects of diffuse and collimated beam radiation on plume formation in natural convection within a cubical enclosure

Abstract

In this paper, a comprehensive numerical simulation of coupled natural convection with diffuse and collimated beam irradiation has been performed in a cubic cavity. The cavity is convectively heated from the bottom; all four vertical walls of the cavity are isothermal and the top wall is adiabatic. A semitransparent window is created on the left wall of the cavity and a collimated beam is irradiated on this window at the polar and azimuthal angles of 900 and 1350, respectively. The numerical analysis has been performed for the transparent(τ=0) and the participating (τ=2.5 and 10) media within the cavity and keeping the value of other parameters, like Rayleigh number (Ra=105), Prandtl number (Pr=0.71), conduction-radiation parameter (N=1.5), irradiation (G=1000W/m2) fixed. The results reveal a quadrantal symmetry of fluid flow and heat transfer for various optical thicknesses and the cavity contains four conical vortices where each vortex is occupied in tetrahedron space in case of without collimated irradiation. Moreover, the Q-criterion reveals the formation of a mushroom like fluid-structure inside the cavity. However, with the inclusion of collimated irradiation, the quadrantal symmetry breaks and a bilaterally symmetric nature is established about the plane of the collimated beam. The flow structure becomes much more complex and has been explained by critical flow theory. In addition, the heat transfer characteristics also change in accordance with the dynamics of vortices inside the cavity. The Q-criterion reveals the formation of non-regular fluid structure which is same, however, orientation is opposite in the cavity for transparent and participating media.