Purely elastic flow asymmetries in flow-focusing devices

• Type: Article in International Scientific Journal
• Date: 2009

Authors

Oliveira, MSN (Author) Other; Pinho, FT (Author) FEUP; Poole, RJ (Author) Other; Oliveira, PJ (Author) Other; Alves, MA (Author) FEUP

Journal

Title: Journal of Non-Newtonian Fluid Mechanics

Vol. 160 No. 1

Pages: 31-39

ISSN: 0377-0257

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 35 Citations

ISI Web of Science

Scopus - 39 Citations

INSPEC

COMPENDEX

Scientific classification

FOS: Engineering and technology > Mechanical engineering

CORDIS: Technological sciences

Other information

Authenticus ID: P-003-HXD

DOI: 10.1016/j.jnnfm.2009.02.010

Abstract (EN): 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. De(c) approximate to 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9