Heat transfer measurements are reported for a rotating 4:1 aspect ratio (AR) coolant passage with ribs skewed $45deg$ to the flow. The study covers Reynolds number (Re) in the range of 10,000–70,000, rotation number (Ro) in the range of 0–0.6, and density ratios (DR) between 0.1 and 0.2. These measurements are done in a rotating heat transfer rig utilizing segmented copper pieces that are individually heated, and thermocouples with slip rings providing the interface between the stationary and rotating frames. The results are compared with the published data obtained in a square channel with similar dimensionless rib-geometry parameters, and with the results obtained for a 4:1 AR smooth channel. As in a 1:1 AR channel, rotation enhances the heat transfer on the destabilized walls (inlet-trailing wall and outlet-leading wall), and decreases the heat transfer ratio on the stabilized walls (inlet-leading wall and outlet-trailing wall). However, the rotation-induced enhancement/degradation for the 4:1 rectangular channel is much weaker than that in the square ribbed channel, especially in the inlet (the first passage). The results on the inlet-leading wall are in contrast to that in the smooth channel with the same AR, where rotation causes heat transfer to increase along the inlet-leading wall at lower Reynolds number ($Re=10,000$ and 20,000). Higher DR is observed to enhance the heat transfer on both ribbed walls in the inlet (the first passage) and the outlet (the second passage), but the DR effects are considerably weaker than those in a ribbed square channel. Measurements have also been parameterized with respect to the buoyancy parameter and results show the same general trends as those with respect to the rotation number. In addition, pressure drop measurements have been made and the thermal performance factor results are presented.

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