Development and performance research of a helical longitudinal-groove tube with secondary flow reinforcement for heat transfer.

The secondary flow has a strong promotion effect on heat transfer in the tube. In order to further utilize the secondary flow phenomenon to strengthen heat transfer of the helical tube, in this paper, a secondary flow enhanced heat transfer helical tube is developed, and stable secondary flow with high strength is obtained. The structure parameters are optimized with the highest comprehensive evaluation factor as the goal. The results show that compared with helical transverse-groove tube and helical grooved tube, helical longitudinal-groove tube has the best heat transfer performance. The new structure's enhanced heat transfer effect for high- Pr number fluid is better than that of low- Pr number fluid, and the enhanced heat transfer effect is not affected by the inlet Reynolds number. The helical angle of helical groove has a greater influence on the comprehensive evaluation factor, while the groove depth and the number of heads have a smaller influence on the comprehensive evaluation factor. The optimal parameter scheme is: The groove depth is 0.5 mm, the helical angle of helical groove is 82°, the head number of helical groove is 1, the comprehensive evaluation factor of helical longitudinal-groove tube compared with ordinary helical tube is 1.173 • The secondary flow and heat transfer characteristics of helical longitudinal-groove tubes are investigated. • Slotting near the vertical direction of the cross-section has a greater impact on the formation of secondary flow. • The heat transfer enhancement effect of the high Pr number working fluid is better than the small Pr number working fluid. • The structural parameters are optimized by multi-factor orthogonal test and local parameter single-factor analysis method. [ABSTRACT FROM AUTHOR]