This paper experimentally investigated the bubbly-intermittent flow (BI) transition in helically coiled tubes (HCT) with coil diameter of 20, 40 and 80cm. A double sensor conductivity probe and a high-speed camera were used to obtain local phase distribution parameters and flow imagery. Because of the centrifugal force, buoyancy was redirected and enhanced, leading to a highly asymmetry and concentrated bubble distribution. As a result, BI transitions occurred at much lower gas flow rates in HCTs. Observation of the BI transition revealed two mechanisms: bubble accumulation in flow direction due to bubble velocity difference (liquid superficial velocity lower than 1.5m/s), and bubble accumulation in radial and peripheral direction due to strong buoyancy (liquid superficial velocity higher than 1.5m/s). The critical void fraction at which BI transition occurred (e.g., α =0.065 for coil diameter of 40cm) increased as the coil diameter increased, and was much lower than that of straight tubes (α =0.25–0.51). A correlation predicting BI transition was established, covering both straight inclined tubes and HCTs; which met the experimental results well when the coil diameter was larger than 0.2m.

中文翻译：

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螺旋盘管中的气泡间歇性流动过渡

本文实验研究了盘管直径为20、40和80cm的螺旋盘管（HCT）中的气泡间歇流动（BI）过渡。使用双传感器电导率探头和高速相机获取局部相分布参数和流动图像。由于离心力，浮力被重定向和增强，导致高度不对称和集中的气泡分布。结果，HCT中的气体流速低得多时，BI转变就发生了。BI过渡的观察揭示了两种机制：由于气泡速度差（液体表面速度低于1.5m / s）而在流动方向上的气泡累积，以及由于强浮力（液体表面速度高于1.5）而在径向和圆周方向上的气泡累积。多发性硬化症）。BI过渡发生的临界空隙率（例如，对于40cm的线圈直径，α= 0.065）随着线圈直径的增加而增加，并且远低于直管（α= 0.25-0.51）。建立了一个预测BI过渡的相关性，涵盖了直斜管和HCT。当线圈直径大于0.2m时，与实验结果吻合较好。