Experimental investigations on heat transfer enhancement for a high aspect ratio rectangular duct roughened by intersecting ribs with inclined ribs

In this work, the effect of the intersecting ribs with inclined ribs on the heat transfer performance and friction factor through a rectangular roughened duct have been experimentally investigated. The chosen aspect ratio of the duct (W/H) was 10 and Reynolds number was in the range between 35,700 up to 72,800. The ribpitch-to-height-ratio (P/e) and Relative roughness height (e/Dh) were 10 and 0.068 respectively. The inclination of the rib with respect to the flow, generates counter-rotating secondary flow along the span that causes span wise variation of heat transfer coefficient. The fluid enters at the leading zone of the rib and travel to the trailing zone, thus raising heat transfer rate at the leading zone while the trailing zone heat transfer is relatively low. To minimize this effect, longitudinal ribs were suggested to use with the inclined ribs in intersection form. A single longitudinal rib was installed at the center of the plate with parallel to flow, this for Model 2, and two longitudinal ribs were used for Model 3. Using the intersecting ribs lead to induced new vortices at every intersection point in addition to the primary vorticities at the leading corner of the inclined rib. So, the heat transfer at the trailing zone will enhance. Therefore, the model 3 provide highest Nusselt number ratio than model 2 are about 13.19 % and 7.03%, respectively, with respect to that of the model 1 (without intersecting ribs), Also, it can be observed that the model 3 with two Intersecting ribs mostly provides higher overall efficiency indices rather than those of the model 2 and 1. Copyright © 2019 International Energy and Environment Foundation All rights reserved.