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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >An experimental study on bubble rise path after the departure from a nucleation site in vertical upflow boiling
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An experimental study on bubble rise path after the departure from a nucleation site in vertical upflow boiling

机译：垂直上升沸腾中从成核点离开后气泡上升路径的实验研究

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Visual study was conducted to elucidate the rise characteristics of vapor bubbles after the departure from a nucleation site in forced convective boiling. The flow direction was vertical upward and nearly saturated water was used as a working fluid. The outer surface of a transparent glass tube of 20 mm in inner diameter was electrically heated to generate vapor bubbles inside of the tube. The number density of bubbles in the test section was kept low to observe the behavior of individual bubbles using high speed cameras. The cross-sectional area-averaged velocity of bulk flow was set at 0.5 and 1.0 m/s. The approximate maximum diameter of each bubble was 1.6-2.9 mm. The following observations were made on the behavior of typical bubbles generated in the present experimental conditions: (i) bubbles grew at a nucleation site for a short period of time less than 1 ms with the shape flattened along the vertical heating surface; (ii) bubbles then slid upward the vertical wall for a few millimeters with the gradual increase in their size; (iii) after that, bubbles were detached from the heating surface and migrate towards the bulk flow but they remained close to the wall; (iv) at the instant of detachment, bubble rise velocity was already comparable with the local velocity of surrounding liquid and the rapid growth seen immediately after the nucleation was already completed; (v) after the detachment, bubble size was decreased in slightly subcooled bulk fluid and some of them were collapsed; (vi) bubbles that did not experience the collapse in subcooled liquid reversed the direction of radial migration and was eventually reattached to the wall (vii) after the reattachment, bubbles generally slid upward the vertical surface for a long distance with the gradual growth due to the heat from the heating wall, though the bubbles that experienced larger gap with the wall after the first detachment showed rebounding motion with the reduced amplitude. The detachment from the wall and the reattachment to the wall of bubbles were clearly observed as the typical bubble behavior after the departure from a nucleation site in the present experiments. It was expected that the inertia force and shear induced lift force have the important roles in these phenomena. (C) 2004 Elsevier Inc. All rights reserved.
机译：进行了视觉研究，以阐明在强制对流沸腾过程中从成核位置离开后气泡的上升特征。流动方向为垂直向上，几乎饱和的水用作工作流体。将内径为20 mm的透明玻璃管的外表面电加热，以在管内部产生蒸气气泡。将测试部分中气泡的数量密度保持在较低水平，以使用高速相机观察单个气泡的行为。整体流动的横截面积平均速度设置为0.5和1.0 m / s。每个气泡的近似最大直径为1.6-2.9mm。对在当前实验条件下产生的典型气泡的行为进行了以下观察：（i）气泡在成核点处短于1 ms的短时间内生长，其形状沿垂直加热表面变平; （ii）然后随着气泡尺寸的逐渐增加，气泡在垂直壁上向上滑动几毫米; （iii）此后，气泡从加热表面脱离并向整体流动方向迁移，但气泡仍靠近壁; （iv）在分离的瞬间，气泡上升速度已经与周围液体的局部速度相当，并且在成核完成后立即观察到快速增长; （v）分离后，略微过冷的散装流体中的气泡尺寸减小，其中一些塌陷; （vi）在过冷液体中未经历坍塌的气泡使径向迁移的方向反向，并在重新连接后最终重新附着在壁上（vii），气泡通常会在垂直表面上向上滑动一段较长的距离，并由于来自加热壁的热量，尽管第一次分离后与壁之间出现较大间隙的气泡显示出回弹运动，振幅减小。在本实验中，清楚地观察到气泡从壁上脱离和重新附着到壁上，作为从成核位置离开后的典型气泡行为。可以预料，惯性力和剪切引起的升力在这些现象中起着重要的作用。 （C）2004 Elsevier Inc.保留所有权利。

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