Abstract This study experimentally investigated the heating process of an axially induced cold gas stream in a swirl tubular flame established through tangential fuel/air pre-mixture injection, aiming to clarify the effects of swirl motion on the heat and mass transfer enhancement. Tubular flame burners with geometry swirl numbers (S) of 0.35 to 1.4 were employed in addition to a conventional slit-type burner to systematically study the flame structure, stability, temperature distribution and flow field. The results show that in comparison to the slit burner without rotation, the swirl tubular flame burner provides a much wider range of stable flame from lean to rich limits even under large flow rates. The heating rate of the inner cold stream by the outer burned gas stream increases as the swirl number raises. Cold flow visualization illustrates that the interface between the two streams is rolled up and instability appears at the interface for the larger swirl numbers of S = 0.7 and 1.4, resulting in enhancement of mixing rate. At large flow rates the two streams are well mixed under cold flow condition, however, they are separated and ordered under combustion condition in the upstream, probably resulted from the burned gas expansion outside the central gas stream. While their mixing rapidly enhances as S raises to beyond 0.7. A simple theoretical analysis illustrates that the enhancement of the heating rate with a rotational motion can be quantitatively evaluated by replacing the numeric unity in Eq. (1) with the value of S + 1. The enhancement seems to be through an increase of heat transfer area at low rotational velocities, or increases of heat and mass transfer rates at high rotational velocities.

中文翻译：

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涡流对管状火焰中心气流加热过程的影响

摘要 本研究通过实验研究了通过切向燃料/空气预混喷射建立的涡流管状火焰中轴向诱导冷气流的加热过程，旨在阐明涡流运动对传热传质增强的影响。除了传统的狭缝式燃烧器外，还采用几何涡流数 (S) 为 0.35 至 1.4 的管状火焰燃烧器来系统地研究火焰结构、稳定性、温度分布和流场。结果表明，与不旋转的狭缝燃烧器相比，旋流管状火焰燃烧器即使在大流量下也能提供从稀到浓的更宽范围的稳定火焰。外部燃烧气流对内部冷流的加热速率随着涡流数的增加而增加。冷流可视化表明，当 S = 0.7 和 1.4 的较大旋流数时，两股流之间的界面被卷起，界面处出现不稳定，导致混合速率提高。在大流量下，两股气流在冷流条件下很好地混合，但在上游燃烧条件下，它们被分离和有序，这可能是由于中心气流外的燃烧气体膨胀造成的。当 S 升高到 0.7 以上时，它们的混合会迅速增强。一个简单的理论分析表明，可以通过替换方程中的数值单位来定量评估旋转运动对加热速率的提高。(1) S + 1 的值。增强似乎是通过在低转速下增加传热面积，