Investigation of characteristics of two-phase flows through singularities in microchannels

奇异现象，如弯曲、收缩和/或膨胀，常用于两相微反应器和微型换热器系统中。因此，了解奇异性对微通道内两相流动特性的影响对于开发和设计这类微系统是至关重要的。本研究的目的是研究奇异性和/或液体性质对水平矩形微通道内两相流流型、含气率和压降等流动特性的影响。以蒸馏水、纯乙醇和氢氟醚7200为试验液体，氮气为试验气体。分别以180度回弯、突然收缩和突然膨胀为奇点，每个奇点对应两个不同曲率比和流动面积收缩或膨胀比的矩形微通道。最后，建立了一个新的关联式来预测每个奇点引起的压降。

Singularities, such as bend, contraction and/or expansion, are commonly used in a two-phase micro-reactor and micro-heat exchanger systems. It is thus essential to understand the effects of the singularities on two-phase flow characteristics in microchannel for developing and designing such micro-systems. The purpose of this study is to investigate the effects of singularities and/or liquid properties on two-phase flow characteristics such as flow regime, void fraction and pressure drop in horizontal rectangular microchannels. Distilled water, pure ethanol and Hydrofluoroether 7200 were used as the test liquids, while nitrogen gas as the test gas. 180 degree return bend, sudden contraction and sudden expansion were tested as the singularities, and the two rectangular microchannels for each singularity with different curvature ration and flow area contraction or expansion ratios were used. Finally, a new correlation was developed to predict the pressure drop due to each singularity.