As additional research efforts are conducted, the advantages of using arrays of dimples on the surfaces of internal passages are becoming more apparent. In particular, substantial heat transfer enhancements can be obtained with smaller pressure penalties than provided by other heat transfer augmentation devices, such as rib turbulators. As a result, dimpled surfaces for heat transfer augmentation are encountering wider use in different applications. The purpose of this comment is to point out additional features of the data presented in Fig. 9, which are obtained using a dimpled passage with no rotation.

1 Local and spatially-averaged Nusselt numbers increase as the ratio of dimple depth δ to dimple print diameter $Dp$ increases, provided spherical indentation dimples are used and all other experimental parameters are held constant 20,21. The $δ/Dp$ ratio of the present study is 0.3. Results from other sources, obtained with no...