### Abstract

Language | English |
---|---|

Pages | 31-39 |

Number of pages | 9 |

Journal | Journal of Non-Newtonian Fluid Mechanics |

Volume | 160 |

Issue number | 1 |

DOIs | |

Publication status | Published - Jul 2009 |

### Fingerprint

### Keywords

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

### Cite this

*Journal of Non-Newtonian Fluid Mechanics*,

*160*(1), 31-39. https://doi.org/10.1016/j.jnnfm.2009.02.010

}

*Journal of Non-Newtonian Fluid Mechanics*, vol. 160, no. 1, pp. 31-39. https://doi.org/10.1016/j.jnnfm.2009.02.010

**Purely elastic flow asymmetries in flow-focusing devices.** / Oliveira, Monica; Pinho, F.T.; Poole, R.J.; Oliveira, P.J.; Alves, M.A.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Purely elastic flow asymmetries in flow-focusing devices

AU - Oliveira, Monica

AU - Pinho, F.T.

AU - Poole, R.J.

AU - Oliveira, P.J.

AU - Alves, M.A.

PY - 2009/7

Y1 - 2009/7

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.

KW - elastic asymmetry

KW - converging flow

KW - creeping flow

KW - viscoelastic fluid

KW - PTT model

KW - UCM model

U2 - 10.1016/j.jnnfm.2009.02.010

DO - 10.1016/j.jnnfm.2009.02.010

M3 - Article

VL - 160

SP - 31

EP - 39

JO - Journal of Non-Newtonian Fluid Mechanics

T2 - Journal of Non-Newtonian Fluid Mechanics

JF - Journal of Non-Newtonian Fluid Mechanics

SN - 0377-0257

IS - 1

ER -