Abstract:

Experimental study on temporal and spatial distribution of bubbles during initial stage of static flash of pure water was carried out with depressurization rates varying between 0.27 MPa·s^-1 and 0.64 MPa·s^-1, and the initial height of waterfilm at 0.2 m. The results indicated that bubbles appeared primarily within the stage of pressure’s rapid decline. In terms of temporal distribution, the faster the pressure dropped, the earlier the bubbles turned up, and the faster the number of bubbles increased with time, and also the earlier the bubble number reached its maximum value. In terms of spatial distribution, the number of bubbles grew in trend of “slow-quick-slow” with increasing depth. Small depressurization rate could narrow bubble distribution along depth. At the same depth, the faster the pressure dropped, the larger the bubble number was. At the end of pressure’s fast decline, the relative bubble number had a peak value with increasing depth. Finally, above experiment results were fitted into a pair of correlations for the temporal and spatial distribution of bubbles. Their calculation results matched well with experimental results.

Key words: static flash, bubble, temporal distribution, spatial distribution, depressurization rate

摘要：

设计搭建了静态闪蒸实验台，利用高速摄像对不同压降速率下纯水静态闪蒸起始阶段气泡群的时间和空间分布规律开展了实验研究。实验中液膜初始厚度为0.2 m，压降速率为0.27～0.64 MPa·s^-1。实验结果表明：气泡群主要出现在压力陡降段。在时间分布上，压降速率越大，气泡群出现的时间越早，气泡数目增长越快，且气泡群数目达到最大值所需要的时间越短。在空间分布上，气泡数量随深度呈现了“缓增-陡增-缓增”的增长趋势；压降速率越小，气泡分布越集中；相同深度范围内，压降速率越大，气泡数量越多；至压力陡降段结束时刻，气泡群相对数量随液膜深度的增大有峰值存在。最后，根据实验结果拟合了气泡群时间和空间分布规律的实验关系式，其计算值与实验值吻合良好。

关键词: 静态闪蒸, 气泡群, 时间分布, 空间分布, 压降速率