Influence of channel height on heat transfer augmentation in rectangular channels with two opposite rib-roughened walls

摘要

The twofold geometric variations induced by varying the channel height, namely the w/b and e/b ratios, have demonstrated their combined effects on heat transfer. At the fixed coolant mass flow rate, the decrease of channel height consistently improves heat transfers in the present Re range. Heat transfer augmentation is accompanying with a streamwise heat transfer ripple in each rib pair with the peak values developed on the rib top-surface. Over the back edge of each rib, heat transfers fall radically within the bandwidth of about 0.5-1 rib height to a locally minimum value. In the channel of w/b = 10, the opposite wall effect triggers the mid-rib heat transfer ripple which has led to twin ripples with equivalent Nusselt number peaks over each rib-pitch in the repeated flow region. In conformity with the experimental results, the proposed heat transfer correlation permits the interactive effects of w/b and elb ratios on heat transfer over the repeated flow region to be evaluated. The variation manners of the correlative coefficients m and n with w/b and elb ratios unravel the enhanced rib effect and weakened convective inertia force effect on heat transfer when the channel height reduces. Therefore the selection of channel wlb ratio that provides the maximum heat transfer augmentation for the present rib-floor geometry becomes Reynolds number dependent.