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

摘要： 扭曲管换热器是一种新型高效换热器。在扭曲管强化传热机理研究的基础上，提出了一种新的扭曲管管型——三叶管。验证了标准k-ω湍流模型在圆管及扭曲椭圆管计算中的精确度，并采用该湍流模型对扭曲三叶管Re在4000～20000范围内的传热和流阻性能进行了研究。计算结果表明，扭曲三叶管的Nusselt数比扭曲椭圆管大，虽然压差增大较多但综合传热性能比扭曲椭圆管高。这是由于扭曲三叶管特殊的三叶区结构以及过渡区曲率的变化，使得三叶管内的螺旋流动比椭圆管更为复杂，速度场与温度梯度场的协同程度更好。随着Reynolds数的增大扭曲三叶管的压差及Nusselt数都逐渐增大，但综合性能逐渐降低，在低Reynolds数下扭曲三叶管的强化传热效果较为明显。内切圆直径及过渡圆弧直径越小，扭曲三叶管的综合性能越好，其中内切圆直径的影响更为显著。

关键词: 扭曲管, 三叶管, 场协同, 强化传热