Abstract:

We discuss the onset of a purely elastic flow instability in serpentine channels, using a combined experimental, numerical and theoretical investigation. Good qualitative agreement is obtained between experiments, using dilute solutions of flexible polymers in microfluidic devices, and three-dimensional numerical simulations using the upper-convected Maxwell model [1] The results are confirmed by a simple theoretical analysis, based on the dimensionless criterion proposed by Pakdel & McKinley (PRL, 1996). We then determine the influence of fluid shear thinning on the onset of such purely-elastic flow instabilities and observe that shear thinning has a stabilizing effect on the microfluidic flow [4]. Three-dimensional numerical simulations performed using the White–Metzner model predict similar trends, which are not captured by a
simple scaling analysis using the Pakdel–McKinley criterion.
The good understanding of the onset of elastic instabilities can also be used to determine relaxation times of unknown solutions and we describe a microfluidic rheometer using a serpentine flow channel [2]. In addition, we investigate the structure and magnitude of secondary flows, present in flows of visco-elastic fluids in curved geometries [3,5].

[1] Zilz et al, Geometric scaling of purely-elastic flow instabilities, JFM 712 (2012) 203-218
[2] Zilz et al, Serpentine channels: micro – rheometers for fluid relaxation times, Lab Chip (2014)
[3] Poole et al, Viscoelastic secondary flows in serpentine channels, JNNFM 201 (2013) 10–16
[4] Casanellas et al. Stabilizing effect of shear thinning on the onset of purely elastic instabilities
in serpentine microflows, Soft Matter, 2016, DOI: 10.1039/C6SM00326E
[5] Ducloué et al. Secondary flows of viscoelastic fluids in serpentine microchannels, Microfluid
Nanofluid (2019) 23: 33