Blockage effects in natural convection in differentially heated enclosures

Abstract

Natural convection in a differentially heated enclosure filled with discrete solid objects is analyzed numerically. The effect of six square shaped solid objects on the natural convection in a rectangular enclosure of aspect ratio 2 is addressed for different solid geometrical arrangements and thermal conductivities. The investigation is performed for Ra = 1 x 10(5) and 1 x 10(7) for thermal conductivity ratio between the solid bodies and the fluid (k(r)) of 0.1, 1.0, 10 and 100. The problem aims to clarify the boundary effects associated with the location. size and the thermal conductivities of the solid objects. It is known that natural convection in porous media is highly affected by the boundary phenomena when high permeability is considered. Also, the problem has importance in understanding the thermal equilibrium between the solid and the fluid in permeable media, as well as other applications in which obstacles are unavoidable. It is found that placing the solid bodies near to the walls reduce the rate of heat transfer due to the blockage effects. But, placing low conductor bodies far from the boundary layer region may enhance the rate of heat transfer compared with enclosures: without obstacles. Also, compared with low conductivity bodies; it is found that placing high conductor bodies within the boundary layer enhances the rate of heat transfer. As expected, it is shown that Prandtl number has a weak influence on the predictions for Pr greater than or equal to 0.71.