关键词: 扭曲管, 三叶管, 场协同, 强化传热

Abstract: Twisted tube heat exchanger is a high efficiency self-supporting heat exchanger based on traditional shell and tube heat exchanger.Twisted tubes are used outside of tube, forming self-supporting structure on shell side instead of baffles.In this study, a new type of twisted trifoliate tube with three half oval and transitional arc was developed according to the heat transfer enhancement mechanism of twisted elliptic tube.The standard k-ω model was used for numerical calculation of turbulent flow in circle tube and twisted elliptic tube, and the relative error was acceptable in engineering applications.Then a numerical study on heat transfer and flow resistance of twisted trifoliate tube was carried out with this turbulence model.The results showed that the heat transfer of twisted trifoliate tube was enhanced, by comparison of Nusselt number with the twisted elliptic tube.Although the pressure drop increased a lot, comprehensive performance of twisted trifoliate tube was about 13% higher than that of twisted elliptic tube.Due to the special shape of cross section, the helical flow in the twisted trifoliate tube was more complicated than that in the twisted elliptic tube, and the synergy between velocity field and temperature gradient field was better.The effect of Reynolds number in the range of 4000—20000 was also studied.As Reynolds number increased, the Nusselt number and pressure drop increased, but comprehensive performance was worse. The heat transfer enhancement of twisted trifoliate tube was evident, especially at low Reynolds number. The influence of inscribed circle diameter on Nusselt number and pressure drop was greater than that of transitional arc diameter.Comprehensive performance of twisted trifoliate tube was better at smaller inscribed circle diameter and transitional arc diameter.

Key words: twisted tube, twisted trifoliate tube, field coordination;heat transfer enhancement