Influence of passive wake control on thermal-hydraulic performance of a cylinder confined in wavy channel under high blockage ratios
H.F. Ahmed, F.K. Malik, M.M. Khan
Capital University of Science and Technology, Islamabad, Pakistan
Keywords: drag reduction, wake stability, heat transfer, neural networks, blockage ratio
Abstract
Heat exchange devices involving confined heated cylinders in crossflow require wake stability to minimize hydraulic losses, which are typically accompanied by a considerable loss in heat transfer. To address this problem, passive wake control for laminar flow past a cylinder is introduced in the form of wavy channel walls around the cylinder. The resultant effects on heat transfer and drag are investigated in detail for a range of Reynolds numbers (Re = = 20 - 200), blockage ratios ( b = 0.5 - 0.9) and Prandtl numbers (Pr = 0.25 -100). For the given range of parameters, it is shown that the wavy channel reduces cylinder drag by a minimum of ~ 36 % and a maximum of ~ 95 %, at the expense of ~ 8 % and ~ 40 % loss in heat transfer, respectively, compared to the plane channel. Thermal-hydraulic performance of the wavy channel compared to the plane channel for Pr = 0.744, is improved by ~ 14 % for b = 0.5 and ~ 160 % for b = 0.9. Therefore, the performance enhancement brought about by the wavy channel provides an appropriate trade-off between drag reduction and heat transfer loss.
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