Hydrodynamics of oscillating slug flow inside mini channels: a state of art review

Abstract

Improvements in the fabrication capability have given rise to mini/micro systems for heat and mass transfer operations. The motion of uniform/oscillating menisci or air-plug/liquid slug inside such systems (i.e., capillaries/channels) is a challenging hydrodynamic problem that is relevant in many interesting practical applications. Understanding the hydrodynamics of such flows will help us in manipulating the performance parameters, which will further improve the efficiency of these systems. The present paper is an attempt to review the experimental, theoretical/analytical, and modelling methodologies applied to capillaries to predict these properties. Out of the different flow patterns inside the capillaries, oscillating slug flow has been reviewed intensely. In general, flow properties are well understood and predicted for fully formed unidirectional Taylor bubbles in circular as well as rectangular channels. However, the effect of impurities on interfacial tension cannot be fully accounted so far. In addition, there is still uncertainty about the size of bubbles and slugs, while there is little literature available for oscillating slug flows/meniscus. In view of the state of art on such flows, further recommendations have been made for future research direction to explore various hydrodynamic characteristics.