Experimental and numerical study on natural convection from vertical plates with horizontal rectangular grooves

Natural convection from two-dimensional Vertical plates with horizontal rectangular grooves was studied experimentally and numerically. A Mach-Zehnder interferometer was used in the experiment and the local Nusselt numbers at each groove surface (outer, bottom, inner, and top surfaces) were measured quantitatively from the interferograms. In some cases (grooves of some aspect ratios with low Rayleigh number), the total heat transfer rate from the grooved surface is even smaller than that from a flat plate in spite of the increased surface area; care should be practiced to avoid such cases. As revealed by the numerical analysis, for given conditions, secondary recirculation flows are usually found in the groove. They prevent the main flow from flowing into the groove. As they happen, the heat transfer rate at the inner surfaces is significantly smaller than that at the outer surface. The effect of Rayleigh number for each aspect ratio was studied. The results were summarized using the average Nusselt numbs vs. Rayleigh number correlations. The correlations may be used for selecting proper aspect ratio and dimension. (C) 1998 Elsevier Science Ltd. All rights reserved.