Author(s): P.M. Ligrani
“Dimple Array Effects on Turbulent Heat Transfer and Flow Structure”, Turbulence, Heat and Mass Transfer 5 (Editors: K. Hanjalic, Y. Nagano, S. Jakirlic), Begell House Inc., New York, Wallingford (UK), pp. 59-78, 2006.
Described are the flow characteristics and mechanisms produced by dimpled surface arrays, which are responsible for the heat transfer and friction factor augmentations. These include: (i) shedding of multiple vortex pairs from dimples, (ii) the strong secondary fluid motions within these vortex pairs and associated vortical fluid, (iii) shear layer re-attachment within each dimple, and (iv) periodicity and unsteadiness associated with vortex pair shedding and the flows within individual dimples. Information on such fluid flow phenomena is needed so that turbulence models can be developed which accurately represent the flows, and to provide physical understanding so that additional improvements to dimple array cooling schemes are possible. The effects of dimple array flow phenomena are illustrated and quantified by flow structure, friction factor ratio, and Nusselt number ratio results which are presented as either the dimple depth, or channel height is varied. Overall, these results show that dimple array surfaces provide a means for effective and substantial heat transfer augmentation with relatively small increases in pressure drop penalties.