Passive Control of Convective Transport Phenomena Utilizing an Attached-Detached Rib-Array

Passivecontrolof heattransferalonga thermal boundary layerusinganalternateattached-detachedrib arrayis studied experimentally. Five clearance-to-rib height ratios (c/h =0;0:2;0:4;0:6, and 1.2) are examined in detail to comparetheireffectsontheconvectivetransportbetweentwodifferentribspacingsof Pi/h =5and10.Resultsreveal that altering the rib clearance strongly affects theconvectivetransport for Pi/h =5, but negligibly for Pi/h =10. For c/h > 0:4 the compound ribs for Pi/h= 5:0 have higher averaged heat transfer than those for Pi/h =10, whereas a reversed trend is true for c/h < ‐ 0:2. In the case of Pi/h =5, increasing c/h from 0.2 to 0.4 causes an abrupt jump in the averaged heat transfer and friction because of an alteration of turbulent transport, suggesting a critical rib clearance ratio between c/h =0:2 and 0.4 for the transition of turbulent transport from the cavity e ow to the separated-reattached e ow together with vortex-shedding e ow. In addition, lifting every other rib from the duct wall with c/h =0:4 for Pi/h= 5 enhances the highest heat-transfer rate but also incurs the largest pressure-drop penalty. Correlations of averaged Nusselt number for the compound ribs of Pi/h =5 are developed in terms of Reynolds number for different rib clearances for the e rst time.

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