Electroviscous effects in a Carreau liquid flowing through a cylindrical microfluidic contraction

• Published in: Chemical engineering science Vol. 65; no. 23; pp. 6259 - 6269
• Main Authors: Davidson, Malcolm R., Bharti, Ram P., Harvie, Dalton J.E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2010; Elsevier
• Subjects: Applied sciences; Carreau viscosity model; Chemical engineering; Contraction; Debye length; Density; Electrokinetic; Electroviscous; Exact sciences and technology; Liquids; Mathematical models; Microfluidic; Microfluidics; Pipe flow; Shear-thinning; Surface charge; Viscosity ratio; Electrokinetic; Shear-thinning; Carreau viscosity model; Electroviscous; Contraction; Microfluidic; Viscosity; Shear; Pipe flow; Electrokinetics; Finite volume method; Power law liquid; Modeling; Low Reynolds number; Expansion; Fluid mechanics; Surface charge; Electrolyte solution; Prediction; Ion transport; Charge density; Shear thinning fluid; Electric field; Trend analysis; Pseudoplastic fluid; Microfluidics
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2010.09.011

Electroviscous effects in steady, pressure-driven flow of a Carreau shear-thinning liquid in a cylindrical microfluidic 4:1:4 contraction–expansion at low Reynolds number are investigated numerically by solving the equations governing the flow, the electric field, and ion transport, using a finite volume method. The channel wall is considered to have a uniform surface charge density and the liquid is assumed to be a symmetric 1:1 electrolyte solution. Predictions are presented for a range of values of the shear-thinning parameters in the Carreau model for various surface charge densities and Debye lengths. The apparent/physical viscosity ratio is shown to increase as the degree of shear-thinning increases. Thus the electroviscous effect is stronger in shear-thinning liquids than it is when the liquid is Newtonian, a result previously obtained for uniform pipe flow of power-law liquids. The trend holds true regardless of the choice of surface charge density or Debye length, although the magnitude of the trend decreases as the surface charge density and/or the Debye length is reduced. Comparison between uniform pipe flow of a Carreau liquid and the corresponding power-law liquid that approximates it at large shear rates shows that the apparent/physical viscosity ratios for the two models are almost identical. A previous prediction that a near-wall region of reduced velocity can occur for pipe flow of a shear-thinning power-law liquid when EDLs are overlapping and surface charge density is elevated is confirmed for a Carreau liquid.