| The heat exchanger is a key equipment to realize energy saving and consumption reducing. Its heat transfer performance and power consumption affect the production efficiency and the level of energy conservation directly. As an important part of energy conservation technologies, heat transfer enhancement technology can improve the heat exchange efficiency of the heat exchanger and energy utilization efficiency effectively.The resistance and heat transfer characteristics of triangular groove twisted tape and perforated twisted tape in heatexchangetube are experimentally investigated in this paper, and the experimental results are compared with those obtained from using smooth tube. Test runs are conducted using the water as the working fluid. The results indicate that, in the range of the experiment, the pressure drop of triangular groove twisted tape is1.94-2.23times as large as plain tube, while the pressure drop of perforated twisted tape is1.62-2.14times as large as plain tube. In addition, all twisted tapes pressure drop is Increased significantly with the twist rate decreasing. Rotating speed of all twisted tape is increased linearly as flow velocity improves; rotation effect of models for20-5-60°triangular groove twisted tape is the best. The Nusselt numbers of60° triangular groove twisted tape are better than other twisted tapes. The empirical correlations for pressure drop, friction coefficient, rotating speed, heat transfer coefficient and Nusselt number have also been developed by nonlinear regression analysis.In addition,6different structures of twisted tape were investigated by numerical simulation on this paper too. Simulation results show that, the slotted vane of triangular groove twisted tape enhances the transverse flow of fluid in the tube,2-3whirlpools of fluid are formed obviously on both sides of the twisted tape by the spoiler effect of the slotted vane, and the boundary layer thickness was reduced effectively. But the spoiler effect of the slotted vane result in which the pressure drop of triangular groove twisted tape is greater than the perforated twisted tape and smooth twisted tape. The hole structure of perforated twisted tape is beneficial to the turbulence of the fluid, but the spoiler effect is not obvious. The flow field near slotted vane and hole were analyzed, the results showed that:there is abrupt change of pressure drop near hole of perforated twisted tape, while there is velocity mutation phenomenon near the slotted vane. |
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