Fumiyoshi Kimura

Heat transfer and fluid flow of natural convection adjacent to upward-facing horizontal plates

Abstract Natural convective flows over upward-facing horizontal plates were investigated experimentally. The main concerns were the fluid flow and local heat transfer characteristics over a wide range of modified Rayleigh numbers from 10 6 to 10 15 . Test plates 20–1500 mm wide were utilized to attain such Rayleigh numbers and they were heated with uniform heat fluxes. The test fluid was water. The fluid flows over the plates and the surface temperatures of the plates were visualized with dye and by liquid crystal thermometry respectively. Extensive measurements of the local heat transfer coefficients were also carried out. The result from the wide plates showed that the following four regions appear over the plates at a streamwise distance x from the leading edge: (1) a laminar boundary layer region, (2) a streaky, transitional flow region, (3) a turbulent region and (4) a collision region. In particular, the second region covers a considerable portion of the total surface, and the local heat transfer coefficients there decrease proportionately with x. Thus, it was found that the width of the plates exerts a serious influence on the average heat transfer coefficients even at the highest Rayleigh numbers of the present experiments.

Natural Convection over Heated L-corner

Experimental investigations have been carried out on natural convective flows over a heated L-corner in which the vertical plate was shorter than the horizontal plate. Special interest was paid to the fluid flow and heat transfer around the vertical plate. The height of vertical plates, H, were varied as H=10-150mm. The width of horizontal plate was 350mm constant. The test fluid was water. The flow fields and the surface temperatures were visualized with fluorescent dye and liquid crystal thermometry, respectively. The local heat transfer coefficients of the vertical plate were also measured. The result shows that the recirculating flow appears irregularly around the vertical plate when H is less than 30mm. It is also found that the local heat transfer coefficients show a maximum at H/2 when the recirculating flow appears around the vertical plate.

Flow and Heat Transfer of Natural Convection around Upward-Facing Horizontal Plate with a Vertical Plate at the Edge

Natural convective flows around upward-facing horizontal heated plate with a vertical plate at the edge were investigated experimentally. The widths of horizontal heated plates, W, and the heights of vertical plates, H, were varied systematically as W=100-350 mm and H=0-150 mm. The flow fields and the surface temperatures of the horizontal plates were visualized with dye and liquid crystal thermometry. The result shows that the vertical plate blocks incoming flow from the edge, and that the flow entering from the open edge covers the whole horizontal surface when the height of the vertical plate exceeds H/W =0.14 for the adiabatic vertical plate and H/W =0.1 for the heated vertical plate. The local heat-transfer-coefficients of the horizontal plate were also measured. The results show that the vertical adiabatic plate depresses the heat transfer while that the heated vertical plate enhances the heat transfer from the horizontal plates.

Fluid Flow and Heat Transfer of Natural Convection Adjacent to Upward-Facing, Heated Plates Inclined Slightly from Horizontal.

Natural convective flows over upward-facing, inclined plates were investigated experimentally. The attentions were focused on the opposing flows that will appear over the plates inclined slightly from horizontal. The flow fields over the plates and the surface temperatures of the heated plates were visualized with dye and liquid crystal thermometry. The result showed that both the descending and ascending flows appear over the plates when the inclination angle is less than 15°. These flows collide with each other at certain distance from the leading edge and, then, ascend away from the plate as a plume. It was found that the above distance is determined solely by the inclination angle and is independent of sizes and heat fluxes of the plate. The local heat transfer coefficients of the plates were also measured. The result showed that the heat transfer is enhanced slightly by the occurrence of the descending flows.