NUMERICAL INVESTIGATION OF LAMINAR NATURAL CONVECTION HEAT TRANSFER IN SQUARE ENCLOSURE WITH TWO HOT INNER CYLINDERS: THE EFFECT OF ONE ELLIPTICAL CYLINDER WITH VARIOUS ASPECT RATIOS

This study conducted two-dimensional numerical simulations of the natural convection in a square enclosure with two inner hot cylinders: one is circular and the other is elliptical at Rayleigh numbers (Ra) of 10(4) < Ra < 10(6) and a Prandtl number (Pr) of Pr = 0.7 (air). The aspect ratio (AR) of the elliptical cylinder ranging from 0.25 < AR < 4. The flow structures and heat transfer mechanism within a square enclosure were investigated with respect to the transition of the flow regime from steady to unsteady state. The thermal and flow fields reached steady state in the Rayleigh number range of 10(4) < Ra < 10(5), regardless of the variation in aspect ratio. However, at Ra = 10(6), the numerical solutions show time-dependent characteristics in the case of the lower and upper elliptical cylinders except at AR = 4. Thus, the steady or unsteady flow regime is strongly dependent on the Rayleigh number and aspect ratio of the elliptical cylinder. Thus, the variation of the aspect ratio has a significant effect on the heat transfer characteristics at the walls of the enclosure and the surface cylinders.