Abstract
The flow of viscoelastic polymer solutions and their use as displacing agents in porous media are important for industrial applications, such as enhanced oil recovery and soil remediation. The complexity of flow and high elasticity of conventionally used viscoelastic polymer solutions can lead to purely elastic instability in porous media. In this study, we investigate the impact of this instability on displacing capillary entrapments at low Reynolds numbers using a microfluidic approach. Our unique design consists of a single-capillary entrapment connected to two symmetric serpentine channels. This design excludes the effect of viscous forces and enables a direct focus on displacement processes driven solely by elastic forces. After the onset of purely elastic instability, an unstable base flow is observed in the serpentine channels. We discuss that the pressure fluctuations caused by this unstable flow create an instantaneous non-equilibrium state between the two ends of the capillary entrapment. This provides the driving pressure to overcome the capillary threshold pressure and eventually displace the entrapped oil. In our geometry, we observe that the displacement coincides with the emergence of a fully developed elastic turbulent state.
Highlights
The addition of high molecular weight polymers to a Newtonian solvent results in a viscoelastic fluid, i.e., a fluid with intermediate mechanical properties between viscous fluids and elastic solids
In the case of Flopaam 3630, the transition from laminar to fully developed turbulence occurs in the range of c_ % 200 sÀ1 to c_ % 2000 sÀ1, whereas transition for Flopaam 3330 occurs between c_ % 2000 sÀ1 and c_ % 6000 sÀ1. Comparing these shear rates to the shear rate range where we detect displacement of the capillary entrapment in our geometry, in Fig. 4(d), we note that the displacement coincides with transition toward the fully developed turbulent regime
A single-entrapment microfluidic geometry was designed based on serpentine channels to mimic the essential features of flow in porous media, i.e., shear-dominated tortuous pathways
Summary
The addition of high molecular weight polymers to a Newtonian solvent results in a viscoelastic fluid, i.e., a fluid with intermediate mechanical properties between viscous fluids and elastic solids. Large elastic stresses induced during the flow of viscoelastic fluids lead to purely elastic instability even in the absence of inertia, i.e., at low Reynolds numbers.[1,2] As the polymers approach their maximum capacity for alignment with the flow and reach a so-called stretched state, they exert a significant back reaction to the flow above a critical shear rate, c_ crit.[3] In other words, purely elastic instability occurs when the polymer relaxation time exceeds its transit time and elastic stresses are no longer fully dissipated.[4] The excessive elastic stresses elicit an unstable base flow. This unstable flow resembles inertia-induced hydrodynamic turbulent flow below the dissipation scale (Kolmogorov length), which is known as the “Batchelor regime.”[5,6]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
