Three-dimensional natural convection in finned cubical enclosures

Three-dimensional natural convection of air in a cubical enclosure with a fin on the hot wall is numerically investigated for Rayleigh numbers of 103–106. The fin, with a thickness of 1/10 of the cavity side, is placed horizontally on the hot wall. The solid to fluid thermal conductivity ratio (Rk) and the fin width are varied. Because the fin is shorter than the cavity side, the cold flow sweeps the lower fin face and the hot wall at the clearances between the fin sides and the lateral walls, where high vertical velocities are reached. The fin inhibits the frontal and lateral access of fluid to the upper fin face, especially at low Rayleigh numbers. Low values of Rk cause heat transfer reductions. The contribution of the fin faces increases at high Rk causing heat transfer enhancements above 20%, which exceed the ones obtained in most two-dimensional studies. In the range of Ra from 105 to 106, maximum heat transfer rates are found for dimensionless fin widths of 0.6 and 0.8 respectively. It is concluded that for 105 ⩽ Ra ⩽ 106 a fin of partial width is more effective in promoting heat transfer than a fin of full width.