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

Laminar natural convection around a two-dimensional horizontal downward-fac ing plate with rectangular grooves was studied experimentally and numerical ly. A Mach-Zehnder interferometer was used in the experiment and the local Nusselt numbers at each groove surface (outer, upper, left side and right s ide surfaces) were measured quantitatively from interferograms. In some cas es (grooves of some aspect ratios with a low Rayleigh number), the increase of the total heat transfer rate from grooved surface may not be sufficient ly large in spite of the increased surface area. As revealed by the numeric al analysis for the given conditions, secondary recirculation flows are usu ally observed in the groove. The protrusions prevent the main flow from flo wing into the groove and cause recirculations. As they happen, the heat tra nsfer rate at the upper surfaces of the groove is significantly smaller tha n that at the outer surface. The effect of Rayleigh number for each aspect ratio was also studied. The results are summarized using the average Nussel t number versus Rayleigh number correlations. The correlations may be used in selecting proper aspect ratio and dimension. (C) 1999 Elsevier Science L td. All rights reserved.