| In order to improve the efficiency of heat exchanger,many novel enhanced heat transfer devices have been developed and investigated recently.In this study,aiming at the drawback of huge flow resistance of conventional wavy vortex generators,a new type of wavy vortex generator,named wedge-shaped wavy-tape inserts,which is designed from structural bionics,is introduced and investigated.In the Reynolds number range of 600 to 1800,the heat transfer,flow resistance and overall performance in a plain tube fitted with wedge-shaped wavy-tape inserts are compared with those of a plain tube with conventional wavy-tape inserts using numerical simulation.The mechanism of heat transfer enhancement and the reasons for effective drag reduction of the wedge-shaped wavy-tape inserts are explained,and the advancement of the improvement of the wedge-shaped wavy tape structure is analyzed.The results show that the heat transfer enhancement performance of the wedge-shaped wavy-tape inserts is 15.6% to 25.9% lower than that of the conventional wavy-tape inserts,under the same operating conditions and wave amplitude,but the flow resistance caused by the conventional wavy-tape inserts is 93.4% to 269.5% larger than that of the wedge-shaped wavy-tape inserts.Therefore,the overall performance of the wedge-shaped wavy-tape inserts can be increased by 22% compared to the conventional wavy-tape inserts.In addition,the structural parameters of the wedge-shaped wavy-tape inserts are optimized from three aspects,which are the undulating shape of the wave tapes,the size of the wavy tapes relative to the tube diameter and the limitation of the extent of space filled in the tube.The results show that the waveform factor(?)should be at least 15%,preferably greater than 21%,and the period ratio(?)should be within the range of 2 to 2.5.Under this condition,the best overall performance can reach the 2.62 times than that of the plain tube.The empirical formulas about the Nusselt number and the drag coefficient,in which only those data of cases with the amplitude ratio ranging from 0.3 to 0.7 are considered,are given.The maximum deviation of Nu and f between the numerical simulation and empirical formulas is 14%.At last,the research on the influence of the arrangement of the wedgeshaped elements shows that the 4-piece type of arrangement has the best overall performance,and its overall performance can be up to 3.26 times than that of the plain tube.The wedgeshaped wavy-tape insert is a promising technique for laminar convective heat transfer enhancement. |
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