Influences of different arrangements of delta-winglets on thermal-hydraulic performance of vortex-generator insert

Heat transfer enhancement in a tube using the vortex-generator (VG) insert with different arrangements of delta-winglets is investigatedin the current study.Fourteen VG insertswith the longitudinaland forward arrangementof delta-wingletsare made from thealuminum sheets with length of 350 mm, width of 14.5 mm, and thickness of 0.6 mm.The heat transfer and pressure drop results achieved from the use of VG insertsinside the tube are compared with those obtained for the plain tube.It is found that at the transitional flow through the plain tube, Notter-Rouse equation predicts the current experimental Nusseltnumber better than Gnielinski equation.Also, the experimental results reveal that the use of VG inserts inside the tube yields higher heat transfer coefficient and pressure drop than the plain tube, and these parameters augment with increasing the number of delta-winglet. The appropriate tradeoff between the enhanced heat transfer and the friction is found by using a special arrangement of delta-winglets on the VG insert which presents the highest heat transfer coefficient as well as the maximum values of considered performance evaluation criterion (PEC). The maximum PEC of 1.41 is found for this VG insert atthe maximum Reynolds number

Keywords:

Heat transfer enhancement , Vortex-generator insert , Delta-winglet , Different arrangement