A numerical study on heat transfer enhancement and flow structure in enhanced tube with cross ellipsoidal dimples

Flow characteristics and heat transfer performance of enhanced tube with cross ellipsoidal dimples are numerically analysed in this research work. The special arrangement is a conventional plain tube with longitudinal and transverse dimples at each cross-plane. The objective is to present details of flow field structure and heat transfer mechanisms for the dimpled tube. Additionally, effects of dimples depth, pitch and axis ratio on thermal-hydraulic performance also being discussed. The realizable k-ε turbulence model was employed in the numerical simulations with the Re range from 5000 to 30,000. The velocity contour, temperature contour, local streamlines, velocity vectors and Nu were presented to illustrated the heat transfer enhancement mechanisms. From this investigation, it is found that the transverse and longitudinal dimples cause downward flow, improve the flow mixing and reattachment, interrupt the boundary layer and form periodic impingement flows and then greatly improve the heat transfer. Nu of TCED increase with the increase of depth and axis ratio, and decrease with increase of pitch. Under operating condition and geometric parameters considered, the TCED with D = 2 mm, P = 20 mm, R = 2.2 and Re = 5000 obtained the largest PEC value about 1.58.