Experimental and numerical study on natural convection from upward horizontal rectangular grooved fins

Natural convection from two-dimensional upward horizontal rectangular grooved fins was studied experimentally and numerically. A Mach-Zehnder interferometer was used in the experiment and the local Nusselt numbers on each surface (outer, left, bottom, and right surfaces) of the grooves were measured quantitatively by analyzing the interferograms. In some cases (grooves of some aspect ratios in low Grashof number), the total heat transfer rate from the grooved surface is even smaller than that from a non-grooved surface though the surface area is greater; care should be practised to avoid such cases. As revealed by the numerical analysis, a secondary recirculation flow is frequently found in the groove. It prevents the main flow from flowing into the groove. When this happens, the heat transfer rate from the inner surfaces is significantly smaller than that from the outer surface. The results have been compressed by the Nu vs. Gr correlations and they give an important guideline for selecting proper aspect ratio and dimensions for upward horizontal grooved fins.