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Experimental identification of the phenomenon triggering the net vapor generation in upward subcooled flow boiling of water at low pressure

机译:在低压下向上过冷流动沸腾中触发净蒸气生成现象的实验鉴定

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Observation of the bubble behavior was made using a high-speed camera to investigate the mechanisms to cause the net vapor generation in subcooled flow boiling. In the experiments, water was used as the test fluid, the flow direction was vertical upward, and the pressure was kept close to the atmospheric pressure. At high liquid subcooling close to the condition of the onset of nucleate boiling, all the bubbles were lifted off the heated surface immediately after the nucleation to disappear quickly in the subcooled bulk liquid due to condensation. It was found that the void fraction did not increase significantly unless the liquid subcooling became low enough for some bubbles to be reattached to the heated surface after the lift-off. When the reattachment took place, the bubble lifetime was substantially elongated since the bubbles slid up the vertical heated surface for a long distance after the reattachment. The reattachment therefore contributed to an increase in the void fraction. It was concluded that in the experimental con ditions tested in this work, the bubble reattachment to the heated surface was a key phenomenon to cause the sharp increase of the void fraction at the point of net vapor generation.
机译:使用高速相机观察气泡行为,以研究引起过冷沸腾中净蒸气生成的机理。在实验中,将水用作测试流体,流动方向垂直向上,并且压力保持接近大气压。在接近于成核沸腾开始的条件的高液体过冷度下,成核后立即将所有气泡从受热表面上提起,由于冷凝而在过冷的本体液体中迅速消失。已经发现,除非液体过冷度降低到足以使一些气泡在剥离后重新附着到加热表面上,否则空隙率不会显着增加。当重新连接时,由于气泡在重新连接后沿垂直加热表面向上滑动了很长的距离,因此气泡的寿命大大延长了。因此,重新连接导致空隙率的增加。可以得出结论,在这项工作中测试的实验条件下,气泡重新附着到受热表面是导致净蒸汽产生时空隙率急剧增加的关键现象。

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