Fluid Flow and Heat Transfer of Combined Convection over Upward-Facing, Horizontal Circular Disks Placed in Vertical Downward Flow

概要

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Experimental investigations have been carried out on combined convective flows over upward-facing, circular heated disks placed in a vertical downward flow of forced convection. The experiments were performed with air in the ranges of the Reynolds and Grashof numbers as: 100 < ReD < 2×104, 104 < GrD < 107. The flow fields over disks are first visualized with smoke. The results showed that a twin-vortex appears over the disk intermittently when the buoyancy force is beyond a criterion, and that the onset of the above twin-vortex can be predicted with the Richardson number as GrD/ReD2 = 3.1. The overall heat transfer coefficients from the disks were subsequently measured. The results showed that the coefficients are increased significantly from those of the laminar stagnation point flows with the occurrence of the twin-vortex, and that the relative increase in the average Nusselt numbers of the combined convective flows against those of the stagnation point flows can be predicted with the above Richardson number.