Flow of low viscosity Boger fluids through a microfluidic hyperbolic contraction

Laura Campo-Deaño, Francisco J Galindo-Rosales, F.T. Pinho, M.A. Alves, Monica Oliveira

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Abstract

In this work we focus on the development of low viscosity Boger fluids and assess their elasticity analyzing the flow through a microfluidic hyperbolic contraction. Rheological tests in shear and extensional flows were carried out in order to evaluate the effect of the addition of a salt (NaCl) to dilute aqueous solutions of polyacrylamide at 400, 250, 125 and 50 ppm (w/w). The rheological data showed that when 1% (w/w) of NaCl was added, a significant decrease of the shear viscosity curve was observed, and a nearly constant shear viscosity was found for a wide range of shear rates, indicating Boger fluid behavior. The relaxation times, measured using a capillary break-up extensional rheometer (CaBER), decreased for lower polymer concentrations, and with the addition of NaCl. Visualizations of these Boger fluids flowing through a planar microfluidic geometry containing a hyperbolic contraction, which promotes a nearly uniform extension rate at the centerline of the geometry, was important to corroborate their degree of elasticity. Additionally, the quantification of the vortex growth upstream of the hyperbolic contraction was used with good accuracy and reproducibility to assess the relaxation time for the less concentrated Boger fluids, for which CaBER measurements are difficult to perform.
Original languageEnglish
Pages (from-to)1286-1296
JournalJournal of Non-Newtonian Fluid Mechanics
Volume166
Issue number21-22
Early online date23 Aug 2011
DOIs
Publication statusPublished - Nov 2011

Keywords

  • Boger fluids
  • rheology
  • microfluidics
  • relaxation time
  • etensional flow
  • contraction-expansion flow

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