Natural convection around horizontal downward-facing plate with rectangular grooves: experiments and numerical simulations

Laminar natural convection around a two-dimensional horizontal downward-facing plate with 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, upper, left side and right side surfaces) were measured quantitatively from interferograms. In some cases (grooves of some aspect ratios with a low Rayleigh number), the increase of the total heat transfer rate from grooved surface may not be sufficiently large in spite of the increased surface area. As revealed by the numerical analysis for the given conditions, secondary recirculation flows are usually observed in the groove. The protrusions prevent the main flow from flowing into the groove and cause recirculations. As they happen, the heat transfer rate at the upper surfaces of the groove is significantly smaller than that at the outer surface. The effect of Rayleigh number for each aspect ratio was also studied. The results are summarized using the average Nusselt number versus Rayleigh number correlations. The correlations may be used in selecting proper aspect ratio and dimension.