Abstract: In order to improve the performance of laminar heat transfer in a tube, three types of twisted tape with alternate axes were designed. Numerical study was performed on the laminar heat transfer characteristics in circular tubes inserted with these different twisted tapes. The results show that, (1) For the case with short-width twisted tape of alternate axes, Nusselt number (Nu) increases with the increment of the dislocation angle under small Reynolds number (Re); but for large Re, the impact of dislocation angle grows negligible. However, a sudden decrease of Nu occurs at large Re for the small dislocation angles cases. The dislocation angle has an insignificant effect on the friction factor (f). The value of performance evaluation criterion (PEC) is the highest for the case with a 90° dislocation angle. (2) For the case with center-cleared twisted tape of alternate axes, the largest Nu is reached at the 60° dislocation angle. The friction factor f is relatively larger than that when the dislocation angle is 0°, and it exhibits an obvious increment with the dislocation angle. The PEC value demonstrates a complex variation with the dislocation angle. However, in general, the thermo-hydraulic performance is the best for the case with a 60° dislocation angle. (3) For the case with center-cleared short-width twisted tape of alternate axes, the Nu increases with the increment of the dislocation angle under small Re; but at large Re, the differences for different dislocation angle is limited. The dislocation angle has an insignificant effect on the friction factor (f). The PEC value is the highest for the case with a 90° dislocation angle. But the sudden decrease of Nu does not occur at large Re for the small dislocation angles cases. The largest f appears when the dislocation angle is 60°, but the differences between the cases with different dislocation angles are small. Moreover, the friction factor f is reduced by a great extent as compared with short-width twisted tape of alternate axes. The variation tendency of PEC is similar to that of Nu, and it performs best at the 90° dislocation angle. (4) In summary, a better comprehensive thermo-hydraulic performance could be obtained by applying the center-cleared short-width twisted tape of alternate axes.

Key words: heat transfer, laminar flow, twisted tape with alternate axes, short-width twisted tape, center-cleared twisted tape, numerical simulation

摘要： 为了提高管内层流换热性能，开发了三种不同的交替轴扭带作为强化换热的扰流元件。通过数值模拟对内置这些扰流元件的管内换热与流动特性进行了研究，结果表明：（1）对于交替轴窄边扭带，在较低Reynolds数下Nusselt数随错位角的增大而增大；而Re较高时，错位角的影响较小。阻力系数f随错位角的变化不大，90°对应的综合性能指标PEC最高。（2）对于交替轴中空扭带，Nu在60°时达到最大值，f随错位角的增加而有较明显的增加，PEC在60°时最好。（3）对于交替轴窄边中空扭带，Re较低时，Nu随错位角增大而增加；而Re较高时，错位角的影响较小。f的最大值出现在错位角为60°时，但错位角的影响并不明显，而且比交替轴窄边扭带的f降低很多。90°错位角对应的PEC最好。（4）总体来看，采用交替轴窄边中空扭带能全面获得优良的热-水力学综合性能。

关键词: 换热, 层流, 交替轴扭带, 窄边扭带, 中空扭带, 数值模拟