Figure 16 Nusselt number ratio distribution for case b

With rotation the results show that the rotation significantly increases the Nusselt number ratio on the first pass trailing surface and the second pass-leading surface. The rotating Nusselt number ratios on the first pass trailing and second pass leading surface are higher than in the non-rotating case, while the first pass leading and second pass trailing surfaces are lower. This is because of the combined effect of the rib induced secondary flow and the rotation induced secondary flow vortices, as shown in Fig. 1.4-b. The Nusselt number ratio has the same trend as stationary case except the leading surface first pass shows continuous decreasing and then increase at the 180° turn. In the 180° turn, the leading surface Nusselt number ratio shows higher value compared to trailing surface.

For 135° channel orientation, the result also shows that rotation enhances the heat transfer in the first pass-trailing surface and second pass leading surfaces, whereas the heat transfer decreases in the first pass leading and second pass trailing surfaces. In the 135° orientation, the heat transfer surfaces are not orthogonal to the plane of rotation, and the rotational effects are less significant when compared with 90° orientation, as shown in Fig. 1.4-b The effect of Coriolis forces on the first pass trailing and second pass leading surfaces for 90° rotation is more since the two counter vortices are normally incident on trailing surface first pass and leading surface second pass. Thus greater differences between leading and trailing Nusselt number ratio in each pass are observed in the 90° orientation. Hence, the differences in Nusselt number ratio between leading and trailing surfaces are not as significant for the 135° orientation as they are for the 90° orientation. In the 180° turn, the leading surface shows slightly better Nusselt number ratio than trailing surface. The results also show that the rotation effect decreases with increasing Reynolds number (or decreasing rotation number).

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