Abstract: With air-water as working fluid, the gas-liquid two-phase flow pattern and evolvement characteristics in a microchannel with periodic expansion-constriction cross sections were investigated experimentally by means of IDT high-speed camera mounted together with a Nikon microscope.The observed flow patterns were intermittent flow and separated flow.For intermittent flow, gas scattered in liquid phase or liquid scattered in gas phase, and the two forms appeared in turn.For separated flow, gas flowed mainly along the wall side of gas inlet, and liquid flowed mainly along the liquid side of water inlet.There was an obvious interface between two phases and the interface fluctuated along the flow direction.According to gas phase and liquid phase superficial velocities, flow pattern maps were drawn and correlations for describing flow pattern transition in the newly proposed microchannels were obtained.It was found that for a given liquid phase superficial velocity, the flow pattern transition gas phase superficial velocity for the microchannel with triangular reentrant cavities was slightly smaller than that for the microchannel with fan-shaped reentrant cavities.

Key words: periodic expansion-constriction, microchannel, two-phase flow pattern, evolvement characteristic

摘要： 以空气和水为实验工质,利用IDT高速摄像仪和Nikon生物显微镜组成的可视化系统对水平放置的PDMS周期性扩缩微通道内的气液两相流型及其演变特性进行实验研究。观察到的主要流型为间歇流和分离流。对于间歇流,气体以离散形式分布在液相中或者是液体以分散形式分布在气相中,而且气相分散跟液相分散交替存在。对于分离流,气体主要沿气体进口壁侧流动,液体主要沿液体进口壁侧流动。两相中存在明显的分界面,沿流动方向界面产生波动。通过改变气液两相表观流速,得到气液两相流型分布,进而提出间歇流与分离流流型转换的准则关系式。结果表明,同一液相表观流速下,三角凹穴型微通道间歇流向分离流转变所需的气相表观流速略小于扇形凹穴微通道。

关键词: 周期性扩缩, 微通道, 两相流型, 演变特性