Experimental Studies of Liquid-Liquid Displacement in Microchannels with Pure Viscoelastic Fluids*

Displacement of one liquid by another is very common in a number of applications including cleaning of pipes and EOR. Previous studies have considered displacement of  Newtonian fluids, while often in applications the fluids involved are viscoelastic.

In this study, the immiscible displacement of a Newtonian organic liquid by a pure viscoelastic aqueous liquid (known as Boger fluid) was investigated inside a straight circular microchannel. High speed imaging was employed to observe the displacement behaviour using different image processing techniques.

The results at the initial viscous finger front showed a slightly thinner trapped film when displacement was performed with the Boger liquid, compared to the Newtonian case. In addition, the time it takes for the interface to become unstable was shorter by up to 50% for the Boger fluid. The natural modes of instability were categorised by mean of interface tracking and post-processing techniques such as 1-D wavelet transformation. Two main types of instability were observed, namely axisymmetric and asymmetric. Brightfield particle image velocimetry techniques were also employed to observe the velocity field during the instabilities.