flow is about 2–3.5 times of smooth-walled channel
level. The flow structure produced by dimpled surface
is characterized by vortical fluid and vortex pairs those
periodically shed from each dimple. A large up-wash
region and packets of fluid emanating from the central
regions of each dimple, accompanying with the periodically
vortex shedding process, develop in the region near
the dimple diagonals. This complex three-dimensional
unsteady process results in the effective heat transfer
enhancements over the flat parts of the dimpled surface.
But the heat transfer elevation in the concave dimpled
surface is less effective.