The present paper reports heat-transfer enhancement and the corresponding pressure drop over a ยฏat surface in a channel ยฏow due to perforated rectangular cross-sectional blocks attached on its surface. The channel had a cross-sectional area of 80 ร 160 mm 2 with blocks 10 ร 25 mm 2 . The experiments covered the following range: Reynolds number (Re) 6670ยฑ40 000, the hole inclination angle h 0ยฑ45ยฐ, the perforation open-area ratio / 0.05ยฑ0.15, the diameter of the perforations (D) 2.5ยฑ8.0 mm, and the number of the blocks N b 2ยฑ7 (giving the ratio of the distance between the blocks to the channel hydraulic diameter (S x =D e ) 1.407ยฑ0.309). The blocks were transverse to the main ยฏow. It was observed that the heat-transfer enhancement increased with increasing h; / and D and decreasing S x =D e and Re. The pressure drop was not aected by h while it decreased with increasing D, Re, S x =D e , and /. Correlation equations were developed for the average Nusselt number (Nu) and the friction factor (f). Performance analysis indicated that the solid blocks could lead to energy loses up to 20% despite signiยฎcantly enhanced heat-transfer due to the increased surface area. The energy lost was recovered by perforations opened in the blocks by which means it was possible to achieve energy gains up to 40%.