Purely elastic flow asymmetries in flow-focusing devices

Monica Oliveira, F.T. Pinho, R.J. Poole, P.J. Oliveira, M.A. Alves

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

The flow of a viscoelastic fluid through a microfluidic flow-focusing device is investigated numerically with a finite-volume code using the upper-convected Maxwell (UCM) and Phan-Thien–Tanner (PTT) models. The conceived device is shaped much like a conventional planar “cross-slot” except for comprising three inlets and one exit arm. Strong viscoelastic effects are observed as a consequence of the high deformation rates. In fact, purely elastic instabilities that are entirely absent in the corresponding Newtonian fluid flow are seen to occur as the Deborah number (De) is increased above a critical threshold. From two-dimensional numerical simulations we are able to distinguish two types of instability, one in which the flow becomes asymmetric but remains steady, and a subsequent instability at higher De in which the flow becomes unsteady, oscillating in time. For the UCM model, the effects of the geometric parameters of the device (e.g. the relative width of the entrance branches, WR) and of the ratio of inlet average velocities (VR) on the onset of asymmetry are systematically examined. We observe that for high velocity ratios, the critical Deborah number is independent of VR (e.g. Dec ≈0.33 for WR= 1), but depends non-monotonically on the relative width of the entrance branches. Using the PTT model we are able to demonstrate that the extensional viscosity and the corresponding very large stresses are decisive for the onset of the steady-flow asymmetry.
LanguageEnglish
Pages31-39
Number of pages9
JournalJournal of Non-Newtonian Fluid Mechanics
Volume160
Issue number1
DOIs
Publication statusPublished - Jul 2009

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Asymmetry
virtual reality
asymmetry
entrances
Branch
Critical Threshold
Newtonian fluids
Viscoelastic Fluid
unsteady flow
steady flow
Newtonian Fluid
Microfluidics
Steady flow
Unsteady Flow
Unsteady flow
Steady Flow
Finite Volume
slots
fluid flow
Fluid Flow

Keywords

  • elastic asymmetry
  • converging flow
  • creeping flow
  • viscoelastic fluid
  • PTT model
  • UCM model

Cite this

Oliveira, Monica ; Pinho, F.T. ; Poole, R.J. ; Oliveira, P.J. ; Alves, M.A. / Purely elastic flow asymmetries in flow-focusing devices. In: Journal of Non-Newtonian Fluid Mechanics. 2009 ; Vol. 160, No. 1. pp. 31-39.
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Purely elastic flow asymmetries in flow-focusing devices. / Oliveira, Monica; Pinho, F.T.; Poole, R.J.; Oliveira, P.J.; Alves, M.A.

In: Journal of Non-Newtonian Fluid Mechanics, Vol. 160, No. 1, 07.2009, p. 31-39.

Research output: Contribution to journalArticle

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AU - Oliveira, Monica

AU - Pinho, F.T.

AU - Poole, R.J.

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N2 - The flow of a viscoelastic fluid through a microfluidic flow-focusing device is investigated numerically with a finite-volume code using the upper-convected Maxwell (UCM) and Phan-Thien–Tanner (PTT) models. The conceived device is shaped much like a conventional planar “cross-slot” except for comprising three inlets and one exit arm. Strong viscoelastic effects are observed as a consequence of the high deformation rates. In fact, purely elastic instabilities that are entirely absent in the corresponding Newtonian fluid flow are seen to occur as the Deborah number (De) is increased above a critical threshold. From two-dimensional numerical simulations we are able to distinguish two types of instability, one in which the flow becomes asymmetric but remains steady, and a subsequent instability at higher De in which the flow becomes unsteady, oscillating in time. For the UCM model, the effects of the geometric parameters of the device (e.g. the relative width of the entrance branches, WR) and of the ratio of inlet average velocities (VR) on the onset of asymmetry are systematically examined. We observe that for high velocity ratios, the critical Deborah number is independent of VR (e.g. Dec ≈0.33 for WR= 1), but depends non-monotonically on the relative width of the entrance branches. Using the PTT model we are able to demonstrate that the extensional viscosity and the corresponding very large stresses are decisive for the onset of the steady-flow asymmetry.

AB - The flow of a viscoelastic fluid through a microfluidic flow-focusing device is investigated numerically with a finite-volume code using the upper-convected Maxwell (UCM) and Phan-Thien–Tanner (PTT) models. The conceived device is shaped much like a conventional planar “cross-slot” except for comprising three inlets and one exit arm. Strong viscoelastic effects are observed as a consequence of the high deformation rates. In fact, purely elastic instabilities that are entirely absent in the corresponding Newtonian fluid flow are seen to occur as the Deborah number (De) is increased above a critical threshold. From two-dimensional numerical simulations we are able to distinguish two types of instability, one in which the flow becomes asymmetric but remains steady, and a subsequent instability at higher De in which the flow becomes unsteady, oscillating in time. For the UCM model, the effects of the geometric parameters of the device (e.g. the relative width of the entrance branches, WR) and of the ratio of inlet average velocities (VR) on the onset of asymmetry are systematically examined. We observe that for high velocity ratios, the critical Deborah number is independent of VR (e.g. Dec ≈0.33 for WR= 1), but depends non-monotonically on the relative width of the entrance branches. Using the PTT model we are able to demonstrate that the extensional viscosity and the corresponding very large stresses are decisive for the onset of the steady-flow asymmetry.

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