Comparison with Ribbed Channel

When the results of this investigation are compared with the ribbed channel investigated by Griffith et al. [8], we can see that the dimpled channel behaves somewhat similarly to the ribbed channel of the same geometrical and flow parameters. Some exceptions include the absence of spanwise variations for the orthogonal (b=90°) dimpled channel under rotation. Spanwise variations were quite significant in the case of the ribbed rotating channel due to the 45° rib-angle effect. Also, symmetry is achieved between the two side surfaces (inner and outer) for the orthogonal dimpled channel, which again was not the case for the orthogonal 45° ribbed channel. For the twisted channel (b=135°), the dimple induced secondary flow does not dominate the Coriolis vortices quite as much as the ribbed channel, which was shown to dominate the rotation induced secondary flow. This is evident in the emergence of the dimpled trailing-outer surface as the primarily enhanced surface for the twisted dimpled channel; the ribbed channel exhibited rib-dominance by producing identical behavior for the leading-outer and trailing outer surface of the twisted channel. From this observation, coupled with the overall slightly lower heat transfer enhancement of the dimpled channel, it can be determined that the dimpled channel does not produce as strong of a secondary flow pattern as the 45° angled-rib channel. However some of the geometrical parameters are possibly not of equivalent value, such as e/D=0.1 for the 45° angled-rib duct and <5Dp=0.3, and <5D=0.094 for the dimpled channel.

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