Results And Discussion

Computations were performed f°r nen-retating (Ro = 0) and rotating (Ro = 0.14) rectangular channels with V-shaped ribs at Reyn°lds number Re = 10,000, and inlet coolant-to-wall density rati°s Ap/p = 0.122. The Nusselt numbers presented here were n°rmalized with a sm°°th tube c°rrelati°n by Dittus-B°elter/McAdams f°r fully devel°ped turbulent n°n-r°tating tube fl°w:

Nuo = 0.023 Re08 Pr04

Figures 2.3(a) and 2.3(b) sh°w the l°cal Nusselt number rati° c°nt°urs °f the leading and trailing surfaces, respectively, f°r the n°n-r°tating case. The entrance and exit regi°ns were cut t° f°cus °n the ribbed heated secti°n. It is seen that the highest Nusselt number rati°s were °btained °n the t°p °f the ribs, and the l°wer Nusselt number rati°s were °btained right bef°re and after the ribs. Between any tw° ribs, the Nusselt number rati°s are highest near the middle section of the channel and decrease gradually towards the sidewalls (i.e., inner or outer surfaces). This is due to the rib induced secondary flow that moves from the center of the V-shaped rib to the sidewalls. In Figure 2.4, the rotation number is increased to 0.14 while the density ratio is kept fixed at 0.122. For the rotating case, the Coriolis forces produce a cross-stream two vortex flow structure that pushes the cold fluid from the core toward the trailing surface and then brings it back along the inner and outer surfaces to the leading surface. This means that the thermal boundary layer starts at the trailing surface, grows along the two side surfaces and ends at the leading surface. This results in small temperature gradient near the leading surface (hence lower heat transfer coefficients) and steeper one near the trailing surface (hence higher heat transfer coefficients). Moreover, the cooler heavier fluid near the trailing surface will be accelerated by the centrifugal buoyancy force while the hotter lighter fluid near the leading surface will be decelerated to maintain the continuity in the streamwise direction. The Coriolis and centrifugal buoyancy forces cause the Nusselt number ratios on the trailing surface to increase compared to the non-rotating case. On the other hand, the Nusselt number ratios were reduced on the leading surface comparing to the non-rotating case.

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