Crossed 45 Vshaped Rib Case

Figure 1.7 shews the Nusselt number distributicn for crossed rib case (see figure 1.4-c). The result sh°w that the non-rotating Nusselt number rati°s unlike the parallel rib case. B°th sides °f the principle surfaces are n°t identical and they have l°wer Nusselt number rati°s. The peak value in the first pass-trailing surface appears at the entrance, while the peak value °n the leading surface appears at the middle °f the channel. This variati°n is due t° the different °rientati°ns °f the 45° V-shaped ribs that are placed on the principle surfaces and cause the dissimilarity. It is also noticed that the 45° V-shaped ribs that are placed on the leading surface produce higher Nusselt number ratio than the inverted 45° V-shaped ribs on the trailing surface. This is because the stagnation region that was generated by inverted V-shaped ribs (see Figure 1.3). In the second pass, the Nusselt number distributions for both surfaces are almost similar in trend and different in values. The Crossed rib case as seen in Fig. 1.4-c generates two counter rotating vortices, which enhances the Nusselt number distribution. But this enhancement is low compared to the parallel rib case which, induces four counter rotating vortices to increase the mixing and resulting to better heat transfer enhancement. Figure 1.4-c shows that the rotation induced secondary flow vortex pushes the cold fluid toward the trailing surface in the first pass and the leading surface in the second pass. At the same time the ribs induced secondary flows work against the rotation secondary flow. This is limited the mixing between the near surface fluid and the mean stream flow, which reduces the Nusselt number ratio through the entire channel.

-•-Case (a), non-rotation -■- Case (b) non-rotation -o- Case (a), 550 rpm -B- Case (b), 550 rpm

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