Parallel 45 Vshaped Rib Case

Figure 1.6 shows the Nusselt number ratio for case (b). The stationary case results show the highest Nusselt number ratio in the first pass occurs at the entrance region. This peak value is due to the fact that the flow is thermally developing and the two pairs of counter rotating secondary flow vortices that are generated by the inverted 45° V-shaped rib. Then the Nusselt number ratio decreases slightly as the flow becomes thermally fully developed. Immediately the Nusselt number ratio recovers to increase. This is due to the two pairs of counter rotating secondary flow vortices that are generated by the inverted 45° V-shaped ribs. Then, the Nusselt number ratio decreases as the secondary flows are influenced by the 180° turn. As the flow reaching the exit of the first pass, Nusselt number ratio continuously decreases due to 180° turn induced secondary flows. The inlet of the second pass starts from the sharp 180° turn and the Nusselt number profiles differs from the first pass. At the inlet of the second pass, Nusselt number ratio reaches the minimum value. This drop is due to the decay of the turbulence produced by the sharp 180° turn. Beside the 180° turn, the rib orientation may also be responsible for this drop. Then, the Nusselt number ratio increases down stream of the second pass inlet as the secondary flow induced by the 45° V-shaped ribs start to develop after the influences from the 180° turn are damped.

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