MICROFLUDIC APPLICATIONS OF BUBBLE OSCILLATIONS INDUCED BY GEOMETRICAL CONSTRAINT

Abstract

We present an experimental study of the propagation of air finger/bubble through a fluid-filled microchannel with centered rectangular occlusion. The displacement of a wetting fluid (oil) by a non-wetting fluid (air) at a constant flow rate results in a family of steadily propagating fingers/bubbles analogous to the propagation modes recently reported by [15, 16, 17] in millimetre-scale tubes, indicating that gravity is not an essential physical mechanism that underpins the emergence of these states. The occurance of these propagation modes informed by a simple modification of the tube geometry revealed that models based on idealized pore geometries are not able to capture key features of a complex practical flows. As the capillary number increases beyond a critical capillary number, the bubbles either localized in the least-constricted regions of the cross section or exhibit spatial oscillations formed by periodic sideways motion of the interface at a fixed distance behind the moving finger tip. We found that the transition from symmetric to either localized or oscillatory state results fom exchange of stability between two different states rather than a continous evolution from one state to another. Also, our experimental evidence suggests that the propagating fingers are dependent on the dimension of the channel and the obstacle. Our results reveal that air fingers and finite bubbles of aspect ratios greater than one exhibit propagation modes that are both quantitatively and qualitatively similar; but short bubbles with aspect ratios less than one undergo a transition similar to that of a continous transition from one state to another. Our results conform with recent report of [34].

Date of Award	1 Aug 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Anne Juel (Supervisor) & Richard Hewitt (Supervisor)