THE EFFECT OF ADIABATIC WALL ROUGHNESS ELEMENTS ON NATURAL-CONVECTION HEAT-TRANSFER IN VERTICAL ENCLOSURES

The natural convection heat transfer in a two-dimensional vertical enclosure fitted with a periodic array of large rectangular elements on the bottom horizontal wall is investigated numerically. The numerical investigation is carried out for the ranges of Rayleigh numbers (Ra(H)) and aspect ratios (W/H) of 1.85 x 10(2)-1.85 x 10(7) and 0.4-2.4, respectively. Prandtl numbers (Pr) of 0.72 and 4.52 are considered. It is found that the large roughness elements reduce the heat transfer rate across the enclosure. The reduction in heat transfer is more significant for enclosures with W/H > 1. The highest value of heat transfer reduction obtained in this research is 44%. This is obtained for an enclosure with W/H = 2.4 at Ra(H) = 1.85 x 10(4) and Pr = 4.52.