Investigation on the oscillatory dynamics of liquid slugs under pressure fluctuations in a capillary tube

Liquid slug maldistribution can deteriorate mass and heat transfer efficiency of microfluidic slug flow. Among the dominant factors, pressure fluctuations have significant influence on uniformity of slug length and stability of the meniscus morphology. This paper experimentally investigated the hydrodynamic characteristics of an individual liquid slug of different lengths and pinning positions under imposed pressure fluctuations at multiple frequencies. An analytical model was also developed revealing that the liquid slugs behave as a mass–spring–damper system, which corresponds well with the experiment data. The second-order oscillatory dynamic characteristics of liquid slugs revealed in this paper, including the resonant frequencies of liquid slugs and the pressure magnification by a liquid slug, can be useful in optimizing the microfluidic design for overcoming slug flow maldistribution. The findings related to hydrodynamic characteristics of an individual liquid slug can also provide new insights into the pressure transmission inaccuracies in the pinholes of a pressure gauge, as well as sonocrystallization and atomization processes of an acoustic resonant slug in a microreactor.