Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90° and 135° to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45° to the main stream flow. Both 45° parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10000, and 25000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10 and the inlet wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45° parallel ribs produce a better heat transfer augmentation than 45° cross ribs, and a 90° channel orientation produces higher heat transfer effect over a 135° orientation.

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