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An investigation is done in relation to heat transfer enhancement in solar air heaters with circular V-shaped down ribs. Ribs were attached to the absorber plate, having an angle of attack ( = 60 ). The ratio of rib height to hydraulic diameter (e/D) was 0.047, while the range of rib pitch-to-height ratio was (P/e = 4, 8, and 16) mm for three different sheets, with the Reynolds number ranging from (Re = 1825-7759). The roughened wall of the duct is heated by direct sunlight, while the remaining three walls are insulated. The concept of a V-shaped rib was developed to capitalise on this...

The concept of V-shaped rib was developed to capitalize on this span-wise variation of heat transfer for inclined ribs. The V-shaped rib reduced span-wise variation of heat transfer and increased average heat transfer. The heat transfer results have been compared with those for smooth ducts under similar flow and thermal boundary conditions. It is found that the angled ribs give higher heat transfer rate than transverse ribs, because of the secondary flow induced by the rib angle, in addition to breaking the laminar sub-layer and producing local wall turbulence. The results show that the...