The Study On The Heat Transfer Characteristics In Tube With A New Kind Of Twisted Tape Insert

Heat transfer enhancement in tube is validly used in many technology regions. As a passive heat transfer enhancement technology, twisted tape is a simple and effective method. Twisted tape can change the channel of the flow, reduce the thickness of the boundary layer, and then enhance heat transfer. However, twisted tape can also increase the friction factor. As a result, to balance the Nesselt number and friction factor and maintain higher PEC, the main emphasis is put on the modification of the shapes of twisted tapes. A new kind of twisted tape (TTC) was introduced in this paper. Numerical simulation and experimental research was performed to study the effect on heat transfer and friction factor characteristics in a tube with this new kind of twisted tapes insert.In the numerical study, uniform wall temperature was used as the thermal boundary conditions for both laminar flow and turbulent flow. Otherwise, the results were compared with twisted tape without curve (TT) in the periphery region. The results showed that the Nu and friction factor in the tube fitted with TTC were 1.18-1.50 and 2.65-3.22 times of that for the plaint tube in turbulent flow conditions, respectively. The ratio of Nu to Nu0 reduced with the increase of Reynolds number, which indicated that TTC performed better in weak turbulent flow conditions. The PEC for TTC was 1.86-1.02, which was 1.09-1.17 times of that for TT. In laminar flow conditions, the PEC in the tube fitted with TTC were 1.34-1.78 and 1.05-1.13 times of that for the plaint tube and TT, respectively. It can be seen that TTC performed better than TT both in laminar flow and turbulent flow. As a result, TTC was recommended from the view of heat transfer efficiency and material saving.For the limitation of experimental system, only turbulent flow conditions were studied in the experimental study. Four twisted tapes with different length were used in the experimental study. The experimental data revealed that Nu increase with the increase of Re. All these four twisted tapes can cause higher Nu than the plain tube. The twisted tapes also cause higher friction factor, especially for L/l=1.0 and 0.75, with the value of 3.69-5.75 and 2.30-4.48, respectively. The PEC for L/l=1.0,0.75,0.50 and 0.25 is 0.94-1.06,0.82-0.94,0.89-1.04 and 0.89-1.06, respectively. What’s more, characteristic number equation for Nu and f were established in the paper, this can provide theoretical fundamentals for further study.It can be seen from the numerical and experimental study that TTC can enhance heat transfer, especially in weak turbulent flow conditions, which is agree with the physical mechanisms of heat transfer. As a result, further study should put more emphasis on the effect of TTC in laminar flow and weak turbulent flow conditions.