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Two-Phase Flow Across Small Sudden Expansions and Contractions

机译:跨小的突然膨胀和收缩的两相流

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摘要

Two-phase flow approaching singularities such as abrupt expansions and sudden contractions is widely encountered in typical industrial and heat exchanging devices. There have been some studies concerning this subject but they mostly are applicable for larger channels. In this study, the first attempt is made to review the existing efforts concerning two-phase flow across sudden expansions/contractions and to examine the applicability of the existing correlations with respect to the recent data in small channels. The second part of this study presents some newly measured pressure drops and observed flow patterns pertaining to some special flow phenomena by expansion/contraction. For an abrupt expansion, it is found that the existing correlations all fail to provide a reasonably predictive capability against the newly collected data. Furthermore, a unique flow pattern called "liquid jet-like flow pattern " occurs at a very low quality region of total mass flux of 100 kg·m~(-2)·s~(-1), and it raises a setback phenomenon of pressure drop. By contrast, an appreciable increase of pressure difference is seen when the liquid jet-like flow pattern is completely gone. A similar conclusion is drawn for the data of contractions. For the correlations/predictive models, the homogeneous model gives satisfactory prediction for conventional macro-channels but fails to do so when the channels become smaller. This is especially pronounced for a small-diameter tube with a Bond number being less than 1, in which the effect of surface tension dominates.
机译:在典型的工业和热交换设备中,经常遇到两相流逼近奇点,例如突然膨胀和突然收缩。已经对此问题进行了一些研究,但它们大多数适用于较大的渠道。在这项研究中,首次尝试回顾有关突然膨胀/收缩的两相流的现有工作,并检查现有相关性相对于小通道最新数据的适用性。本研究的第二部分介绍了一些新测量的压降和通过膨胀/收缩观察到的与某些特殊流动现象有关的流动模式。对于突然的扩展,发现现有的相关性都不能为新收集的数据提供合理的预测能力。此外,在总质量通量为100 kg·m〜(-2)·s〜(-1)的极低质量区域会出现一种称为“液体喷射状流态”的独特流态,并且会产生挫折现象。的压力下降。相反,当液体射流状流型完全消失时,可以看到压力差明显增加。对于收缩数据得出类似的结论。对于相关性/预测模型,齐次模型可以为常规宏信道提供令人满意的预测,但是当信道变小时,则不能这样做。这对于邦德数小于1的小直径管尤其明显,其中表面张力的作用占主导。

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