Pressure-driven dynamics of liquid plugs in rectangular microchannels: influence of the transition between quasi-static and dynamic film deposition regimes

TL;DR

This study investigates how the transition between quasi-static and dynamic film deposition regimes affects liquid plug dynamics in rectangular microchannels, revealing critical conditions for plug rupture and stable oscillations through experiments and modeling.

Contribution

It introduces a reduced dimension model to predict the transition between regimes and the resulting plug behavior in microchannels with sharp corners.

Findings

Transition causes rapid plug acceleration and rupture.

Stable oscillations occur if in quasi-static regime initially.

Critical initial length predicts regime transition.

Abstract

In this paper, we study experimentally and theoretically the dynamics of liquid plugs in rectangular microchannels for both unidirectional and cyclic pressure forcing. In both cases, it is shown that the transition between quasi-static and dynamic film deposition behind the liquid plug leads to a dramatic acceleration of the plug, rapidly leading to its rupture. This behaviour proper to channels with sharp corners is recovered from a reduced dimension model based on previous theoretical and numerical developments. In addition, it is shown for cyclic periodic forcing that the plug undergoes stable periodic oscillations if it remains in the quasi-static film deposition regime during the first cycle, while otherwise it accelerates cyclically and ruptures. The transition between these two regimes occurs at a pressure-dependent critical initial length, whose value can be predicted theoretically.