Electro-elastic flow instabilities of viscoelastic fluids in contraction/expansion micro-geometries

•Electro-elastic flow instabilities are observed experimentally.•Microfluidic contraction/expansion devices are used.•Dilute and semi-dilute polymer solutions are used.•Instabilities occur for viscoelastic fluid flows above a critical electric field magnitude. Electro-elastic instabilities in electr...

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Bibliographic Details
Published in:Journal of non-Newtonian fluid mechanics 2020-09, Vol.283, p.104293, Article 104293
Main Authors: Sadek, Samir H., Pinho, Fernando T., Alves, Manuel A.
Format: Article
Language:English
Subjects:
Contraction/expansion micro-geometries
Dielectrophoresis
Elastic instability
Electric fields
Electro-elastic instabilities (EEI)
Electro-osmotic flow (EOF)
Fluid flow
Microchannels
Newtonian fluids
Steady flow
Time dependence
Velocity distribution
Viscoelastic fluids
Viscoelasticity
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Summary:•Electro-elastic flow instabilities are observed experimentally.•Microfluidic contraction/expansion devices are used.•Dilute and semi-dilute polymer solutions are used.•Instabilities occur for viscoelastic fluid flows above a critical electric field magnitude. Electro-elastic instabilities in electro-osmotic contraction/expansion flows (EOF) of viscoelastic fluids are experimentally investigated in this work. Several microchannel configurations are used, including the cases with hyperbolic-shaped contractions followed by an abrupt expansion, or abrupt contractions followed by a hyperbolic-shaped expansion. Such cases were selected to assist in the understanding of the EOF instability mechanisms and at which conditions they occur. A reference Newtonian fluid was also used in the experiments, and a wide range of electric fields were imposed to drive the flow. Flow visualizations for a Newtonian fluid allowed to assess the impact of dielectrophoresis on the velocity field of the seeding particles. For each geometry, depending on the polymer concentration, the flow was found to be quasi-Newtonian below a critical electric potential difference, characterized by smooth parallel steady flow patterns in the upstream and downstream channels. Above the critical voltage difference two types of electro-elastic instabilities were found to occur, leading to an unsteady symmetric flow, and to time-dependent irregular flow.
ISSN:0377-0257
1873-2631
DOI:10.1016/j.jnnfm.2020.104293