Effect of Orientation and Aspect Ratio of an Internal Flat Plate on Natural Convection in a Circular Enclosure

This work presents a numerical investigation on natural convection in a circular enclosure with an internal flat plate at Ra = 106. The cross-section area of the plate was fixed at three values, H·W/D2 = 0.01, 0.04, and 0.09, in which H and W are the height and width of the plate and D is the diameter of the enclosure while the aspect ratio changes, which makes the plate vertically placed (H > W) or horizontally placed (H < W). The objective of this work was to explore the effects of the orientation and aspect ratio of the plate on the characteristics of natural convection in various aspects. The numerical results reveal that the overall heat transfer rate is higher for the vertically placed plate and increases with the cross-section area, while the width of the plate has almost no effect for the horizontally placed plate, especially for the plate with a relatively large cross-section area. Depending on the orientation and aspect ratio, there can be one primary vortex, one primary and one secondary vortex, or one secondary and two separated vortices to each side of the plate, and the thermal plume structure may appear at the sharp top corners of the plate. Consequently, local heat transfer on the surfaces of the enclosure and plate is affected. Synergy analysis reveals that the enhancement of heat transfer from the fluid circulation is the most significant at the center of the vortices and at the boundary between them.