Abstract A parametric study is carried out on circular tube with alternating flattened flow path. This analysis is performed numerically with experimental validation on the reference model, which has mid-levels of the design factors. Three design factors, namely straight pitch (a), transient length (b), and minimum axis (c) at five different levels are investigated for 500 ≤ Re ≤ 1500. The main purpose is to enhance the thermal performance of circular tube by producing multi-normal vortices. The results show that new vortices are formed as a result of both increasing Reynolds number and decreasing design factors. Among the studied factors, the minimum axis has the highest effects, followed by the transient length and the straight pitch. Compared to the smooth tube, changing a, b, and c would increase the Nusselt number and frcition factor by 1.34–3.21 and 2.78–4.91, 1.23–4.45 and 2.75–7.5, and 1.04–5.06 and 1.39–16.74, respectively. Almost all enhanced models show an improved thermal performance factor, especially at high Reynolds numbers. The best thermal performance factor is around 2.27 for the model with a = 10, b = 5, c = 5.5 mm. Finally, three correlations are developed for predicting the hydrothermal parameters of such tubes with average errors within 5%.

中文翻译：

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交替扁平流道圆管传热及压降特性参数研究

摘要 对交替扁平流道的圆管进行了参数研究。该分析是通过对参考模型进行实验验证的数值进行的，该模型具有中等水平的设计因素。研究了 500 ≤ Re ≤ 1500 的五个不同水平的直线节距 (a)、瞬态长度 (b) 和最小轴 (c) 三个设计因素。 主要目的是通过生产提高圆管的热性能多法向涡旋。结果表明，由于雷诺数的增加和设计因素的减少，都会形成新的涡流。在研究的因素中，最小轴的影响最大，其次是瞬态长度和直线间距。与光滑管相比，改变 a、b 和 c 会使努塞尔数和摩擦系数增加 1。分别为 34-3.21 和 2.78-4.91、1.23-4.45 和 2.75-7.5，以及 1.04-5.06 和 1.39-16.74。几乎所有增强型模型都显示出改进的热性能系数，尤其是在高雷诺数时。对于 a = 10、b = 5、c = 5.5 mm 的模型，最佳热性能系数约为 2.27。最后，开发了三个相关性来预测这种管的热液参数，平均误差在 5% 以内。