Heat transfer and pressure drop measurements in rib-roughened rectangular ducts

In the present study, the thermal and hydraulic performance of three rib-ro ughened rectangular ducts is investigated. The aspect ratio of the ducts wa s 1 to 8, and the ribs were arranged staggered on the two wide walls. Three rib configurations were tested: parallel ribs and V-shaped ribs pointing u pstream or downstream of the main flow direction. For all cases, the rib he ight-to-hydraulic diameter ratio was 0.06, with an attack angle of 60 degre es and a pitch-to-height ratio of 10. The Reynolds number range was from 10 00 to 6000. Liquid crystal thermography was employed in the heat transfer e xperiment to demonstrate detailed temperature distribution between a pair o f ribs on the ribbed surfaces. The secondary flows caused by the inclined r ibs create a significant spanwise variation of the heat transfer coefficien ts on the rib-roughened wall with high heat transfer coefficient at one end of the rib and low value at the other. In the streamwise direction between two consecutive ribs, the temperature distribution shows a sawtooth fashio n because of flow reattachment. Based on the local heat transfer coefficien ts, the average Nusselt numbers were estimated as weighted mean values. Iso thermal pressure drop data were taken and presented as Fanning friction fac tors. The ducts are compared to each other by considering both heat transfe r and friction factor performance. (C) 2001 Elsevier Science Inc. All right s reserved.