TURBULENT HEAT AND FLUID-FLOW IN A PASSAGE DISTURBED BY DETACHED PERFORATED RIBS OF DIFFERENT HEIGHTS

The spatially periodic turbulent heat transfer and friction in a recta ngular passage of width-to-height ratio of 4:1 with perforated rectang ular ribs detached from one wall have been studied using laser hologra phic interferometry, smoke-streak flow visualization, and pressure pro bing for rib-to-duct hydraulic diameter ratios (H/De) of 0.081, 0.106, and 0.162 and Reynolds number (Re) range of 5 x 10(3)-5 x 10(4). The rib pitch-to-height ratio and the detached distance-to-rib-height rati o are 10 and 0.38, respectively. The laser-Doppler velocimetry measure ments were performed to illustrate the local Nusselt number distributi on. In contrast to the attached solid-type ribs which provide a monoto nic decrease of thermal performance at a constant pumping power (<(Nu) over bar>(p)/<(Nu)over bar>(s)) with increasing rib height, the detac hed perforated-type ribs give a best <(Nu)over bar>(p)/<(Nu)over bar>( s) at a moderate rib height H/De = 0.106 for the lower Re range and a <(Nu)over bar>(p)/<(Nu)over bar>(s) independent of H/De for the high er Re range. In addition, the thermal performance of the detached soli d-type ribs is found to be superior to that of the detached perforated -type ribs and the physical reason for the difference is addressed. (C ) 1998 Elsevier Science Ltd. All rights reserved.