Heat-transfer enhancement in a channel flow with perforated rectangular blocks

The present paper reports heat-transfer enhancement and the corresponding p ressure drop over a flat surface in a channel flow due to perforated rectan gular cross-sectional blocks attached on its surface. The channel had a cro ss-sectional area of 80 x 160 mm(2) with blocks 10 x 25 mm(2). The experime nts covered the following range: Reynolds number (Re) 6670-40 000, the hole inclination angle (0) 0 45 degrees, the perforation open-area ratio (phi) 0.05-0.15, the diameter of the perforations (D) 2.5-8.0 mm, and the number of the blocks (N-b) 2-7 (giving the ratio of the distance between the block s to the channel hydraulic diameter (S-x/D-e) 1.407-0.309). The blocks were transverse to the main flow. It was observed that the heat-transfer enhanc ement increased with increasing theta, phi and D and decreasing S-x/D-e and Re. The pressure drop was not affected by theta while it decreased with in creasing D, Re, S-x/D-e, and phi. Correlation equations were developed for the average Nusselt number ((N) over baru) and the friction factor (f). Per formance analysis indicated that the solid blocks could lead to energy lose s up to 20% despite significantly enhanced heat-transfer due to the increas ed surface area. The energy lost was recovered by perforations opened in th e blocks by which means it was possible to achieve energy gains up to 40%. (C) 2001 Elsevier Science Inc. All rights reserved.