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Visualization study on the mechanisms of net vapor generation in water subcooled flow boiling under moderate pressure conditions

机译:中压条件下水过冷沸腾过程中净蒸气生成机理的可视化研究

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Visualization study using a high speed camera was carried out to explore the mechanisms of net vapor generation (NVG) in subcooled flow boiling. The flow direction was vertical upward, the working fluid was water, and the experiments were conducted under moderate pressure conditions; a rather hydro-philic surface was used as a heated surface. In all the experimental conditions tested in this work, the bubbles nucleated on the heated surface typically departed from the nucleation sites and then slid upward on the vertical heated surface. When the NVG condition was exceeded, the number of bubbles increased noticeably and the range of bubble size became wider with an increase in the thermal-equilibrium quality. It was however found that the rapid increase of the void fraction after the NVG condition was reached could mainly be attributed to the formation of a small number of large bubbles. It was also observed that the large bubbles were mostly produced at the nucleation sites immediately after other sliding bubbles passed over the sites. It was therefore supposed that the production of large bubbles in the wake region that was formed behind the preceding sliding bubbles was a key phenomenon in causing the NVG in the present experiments.
机译:进行了使用高速摄像机的可视化研究,以探讨过冷沸腾过程中净蒸气生成(NVG)的机理。流动方向为垂直向上,工作流体为水,实验在中等压力条件下进行;相当亲水的表面被用作加热表面。在这项工作中测试的所有实验条件下,在加热表面上成核的气泡通常会从成核位置离开,然后在垂直加热表面上向上滑动。当超过NVG条件时,随着热平衡质量的增加,气泡的数量显着增加并且气泡尺寸的范围变宽。然而,发现在达到NVG条件后,空隙率的迅速增加主要归因于少量大气泡的形成。还观察到大气泡主要在其他滑动气泡经过位点后立即在成核位点处产生。因此,可以认为,在本实验中,在前一个滑动气泡后面形成的尾流区域中产生的大气泡是导致NVG的关键现象。

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