Abstract Flow and heat transfer characteristics of impinging jet from pipe nozzle with air-augmented duct were experimentally and numerically investigated. The effects of air-augmented duct geometry on heat transfer enhancement were concerned. The experimental parameters included a diameter (D) and a length (L) of air-augmented duct in the range of D = 2d, 3.3d, 6d, and L = 2d, 4d, 6d where d was the inner diameter of main pipe nozzle at 17.2 mm. The distance from air-augmented duct outlet to impingement surface (S) at S = 2d, 4d and 6d were considered. The conventional impinging jet was also studied to compare the results with the case of an air-augmented duct. The result comparison was based on constant jet mass flow rate by fixing the jet Reynolds number of conventional pipe at Re = 20,000. The temperature distributions on the impingement surface were measured by using a thermal infrared camera, and profiles of velocity and turbulence intensity of the jet were measured by using hot-wire anemometer. The 3-D numerical simulation with SST k-ω turbulence model was also applied to reveal the flow characteristics. The results show that the heat transfer rate on the impingement surface for the case of an air-augmented duct in conditions of 2d ≤ D ≤ 4d and L = 2d is noticeably higher than the case of conventional impinging jets due to increasing air entrainment. The heat transfer rate for the case of D = 6d, L = 2d at S = 2d, is the largest by getting 25.42% higher compared to a conventional impinging jet.

中文翻译：

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空气增强管道通过增加夹带增强撞击射流表面的传热

摘要 通过实验和数值模拟研究了带空气增强管的管嘴冲击射流的流动和传热特性。关注空气增强管道几何形状对传热增强的影响。实验参数包括在D = 2d、3.3d、6d和L = 2d、4d、6d范围内的加气管直径（D）和长度（L），其中d为主管内径喷嘴在 17.2 毫米。考虑了在 S = 2d、4d 和 6d 时从空气增强管道出口到冲击表面 (S) 的距离。还研究了传统的冲击射流，以将结果与空气增强管道的情况进行比较。通过将常规管道的射流雷诺数固定在 Re = 20,000，结果比较基于恒定射流质量流量。使用热红外相机测量撞击表面的温度分布，并使用热线风速计测量射流的速度和湍流强度分布。使用 SST k-ω 湍流模型的 3-D 数值模拟也被应用于揭示流动特性。结果表明，在 2d ≤ D ≤ 4d 和 L = 2d 条件下，空气增强管道的冲击表面的传热率明显高于传统冲击射流的情况，因为增加了空气夹带。在 D = 6d、L = 2d 和 S = 2d 的情况下，传热率最大，与传统的撞击射流相比提高了 25.42%。使用热线风速计测量射流的速度和湍流强度分布。使用 SST k-ω 湍流模型的 3-D 数值模拟也被应用于揭示流动特性。结果表明，在 2d ≤ D ≤ 4d 和 L = 2d 条件下，空气增强管道的冲击表面的传热率明显高于传统冲击射流的情况，因为增加了空气夹带。在 D = 6d、L = 2d 和 S = 2d 的情况下，传热率最大，与传统的撞击射流相比提高了 25.42%。使用热线风速计测量射流的速度和湍流强度分布。使用 SST k-ω 湍流模型的 3-D 数值模拟也被应用于揭示流动特性。结果表明，在 2d ≤ D ≤ 4d 和 L = 2d 条件下，空气增强管道的冲击表面的传热率明显高于传统冲击射流的情况，因为增加了空气夹带。在 D = 6d、L = 2d 和 S = 2d 的情况下，传热率最大，与传统的撞击射流相比提高了 25.42%。结果表明，在 2d ≤ D ≤ 4d 和 L = 2d 条件下，空气增强管道的冲击表面的传热率明显高于传统冲击射流的情况，因为增加了空气夹带。在 D = 6d、L = 2d 和 S = 2d 的情况下，传热率最大，与传统的撞击射流相比提高了 25.42%。结果表明，在 2d ≤ D ≤ 4d 和 L = 2d 条件下，空气增强管道的冲击表面的传热率明显高于传统冲击射流的情况，因为增加了空气夹带。在 D = 6d、L = 2d 和 S = 2d 的情况下，传热率最大，与传统的撞击射流相比提高了 25.42%。