Thermal performance of dimpled surfaces in laminar flows

The present study provides data which illustrate the effects of an array of dimples on local and spatially-averaged surface Nusselt number distributions, as well as on friction factors in channels with laminar flow. Trends of spatially-averaged Nusselt numbers and friction factors are provided as they vary with dimple depth, channel height, Reynolds number from 260 to 1030, and the use of protrusions on the opposite channel wall. When compared with turbulent flow results, the present laminar data illustrate changes due to the absence of turbulence transport. For example, in contrast to turbulent flows, the present laminar flow data show that there is no overall benefit from the use of a top wall with protrusions. In addition, spatially-averaged Nusselt number ratios and friction factor ratios measured on a deep dimpled surface with a smooth top wall show trends which are opposite from ones observed in turbulent flows, since lower laminar heat transfer augmentations are present for smaller channel heights when compared at the same Reynolds number.