宽度交替变化扭旋元件对管内传热特性的影响

在雷诺数Re=200~1 800范围内，利用数值模拟方法对内置宽度交替变化扭旋元件的管内传热性能进行研究，研究结果表明：宽度交替变化扭旋元件能够显著提升努赛尔数Nu和传热性能评价因子η，与光管相比分别提高2.2~5.2倍和1.4~2.2倍；换热管局部努赛尔数沿流向呈速降—缓降—速升—缓降—恒定的变化规律，上升速率随扭旋元件径比的增大而提高，而降低速率与径比关系较小；局部努赛尔数在扭旋元件后方半个元件长度处达到最大值，该长度可作为间隔扭旋元件优选间距；流体在窄扭旋元件以及前后反向扭旋元件作用下，形成主、次螺旋流共存流动，局部流线向中心倾斜，径向流动加强，传热得到强化。

Effect of twisted elements with alternating width on the heat transfer characteristics in a circular tube

The heat transfer characteristics of two twisted elements with alternating width have been studied using numerical simulation methods for Reynolds numbers in the range Re=200-1 800. The results show that, the alternating width of the twisted elements can significantly increase the Nusselt number Nu and the heat transfer performance evaluation factor η, which are, respectively, 2.2-5.2 times higher and 1.4-2.2 times higher than the corresponding values for a plain tube. The local Nusselt number of the heat transfer tube shows a variation of rapid fall, slow fall, rapid rise, slow fall and approximate invariance along the flow direction. The rate of increase of the local Nusselt number increases with the diameter ratio of the twisted element, however, the falling rate is not significantly dependent on the diameter ratio. The local Nusselt number reaches its maximum at a position near the midpoint of the twisted element behind the trailing edge of the front element, this can be used as the optimal gap of the spaced twisted element; Under the action of the narrow twisted element and twisted elements with opposite rotations, primary and secondary swirling flows are formed, the local streamline is inclined to the center, the radial flow is strengthened, and the heat transfer is enhanced.