The influences of 45° V-shaped ribs arrangements, and channel orientation on the leading and trailing Nusselt number ratios in a two-pass rectangular channel have been reported for rotation number from 0 to 0.21 and Reynolds number from 5000 to 40000. The findings are:

1. The general trend of the rotation effect is that increases the Nusselt number ratio in the first pass trailing surface and second pass leading surface, while opposite situation can be observed that low Nusselt number ratio distribution in the first pass leading surface and second pass trailing surface. This is due to the Coriolis and buoyancy forces were generated by rotation. However, the differences between the Nusselt number distributions on the second pass leading and trailing surfaces are smaller than that in the first pass due to the opposite effects of the Coriolis and buoyancy forces.

2. The effects of the Coriolis force and cross-stream flow reduce as the channel orientation changes from b =90° to b=135°. Thus, the Nusselt number ratios for the b=135° first pass trailing and second pass leading surface decreased when compared to their corresponding Nusselt number ratios for the b =90° orientation. The Nusselt number ratios for b=135° first pass leading and second pass trailing surfaces increaded when compared to their corresponding Nusselt number for b =90°.

3. The parallel 45° V-shaped ribs arrangement provides higher heat transfer enhancement compared to the 45° crossed ribs arrangement for both rotating and non-rotating conditions. The crossed rib arrangement shows less rotational effect compared to the parallel rib cases. This is because the 45° parallel rib develops a pair of counter rotating vortices of secondary flows, while the 45° crossed rib develops only a single vortex of secondary flows.

4. The 45° V-shaped rib shows better heat transfer enhancement compared to 45° angled rib (see Azad et al.19). 45° angled rib generates two counter vortices, while 45° V-shaped ribs generates four counter rotating vortices, which promoting more mixing between the near surface fluid (hot) and core fluid (cold).

5. In general, the roughened surfaces in the rectangular channel perform similarly to smooth surfaces with increasing rotational speed. However, the average Nusselt number ratio in the roughened rectangular channel is much higher than the smooth surfaces.

6. For 45° V-shaped ribs cases, results show low Nusselt number ratio in the 180° turn. This is because there in no 45° V-shaped rib placed at the middle of the 180° turn.

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