NT Vortex enhancement of heat transfer and flow in the narrow channel with a dense packing of inclined one-row oval-trench dimples

In the present study it is found that enhancement of air turbulent flow and heat transfer at Re = 10(4) is influenced by a set of one-row oval-trench dimples of depth 0.25 inclined at an angle of 65 degrees to the incoming flow and located at the heated wall of the rectangular (9 x 1) narrow channel when the dimple step H is varied. The periodic section of the dimpled channel 8 in length is considered. The dimple step H is varied from 8 to 2. Abnormal enhancement of flow and heat transfer at H = 2 is followed by both a 4-fold decrease in relative negative friction and a 6.5-fold increase in relative heat transfer in the separated flow zone. A maximum secondary flow velocity in the dimple exceeds by 10% a maximum flow velocity in the plane-parallel channel, reaching 1.27 of bulk flow velocity in the channel. A reason for this phenomenon is associated with forming a very large (up to 1.2) pressure drop between closely spaced zones of high pressure on the windward side of a dimple and of low pressure on its entrance spherical portion. The phenomenon of turbulent flow acceleration with a 1.39-fold increase in the maximum flow velocity (at H = 2) in the dimpled narrow channel in comparison to the plane-parallel channel is discovered. (C) 2019 Elsevier Ltd. All rights reserved.