Oliveira, Monica and Pinho, F.T. and Poole, R.J. and Oliveira, P.J. and Alves, M.A. (2009) Purely elastic flow asymmetries in flow-focusing devices. Journal of Non-Newtonian Fluid Mechanics, 160 (1). pp. 31-39. ISSN 0377-0257Full text not available in this repository. (Request a copy from the Strathclyde author)
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.
|Keywords:||elastic asymmetry, converging flow, creeping flow, viscoelastic fluid, PTT model, UCM model, Mechanical engineering and machinery, Materials Science(all), Chemical Engineering(all), Mechanical Engineering, Applied Mathematics, Condensed Matter Physics|
|Subjects:||Technology > Mechanical engineering and machinery|
|Department:||Faculty of Engineering > Mechanical and Aerospace Engineering|
|Depositing user:||Pure Administrator|
|Date Deposited:||11 Oct 2012 10:59|
|Last modified:||04 May 2016 22:33|