Viscoelastic flow in an obstructed microchannel at high Weissenberg number |
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Authors: | Kevin P Nolan Akshat Agarwal Shenghui Lei Robin Shields |
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Affiliation: | 1.Thermal Management and Eco-sustainability Research Group,Bell Labs Ireland,Dublin 15,Ireland;2.Institute of Petroleum Engineering,Heriot-Watt University,Edinburgh,UK |
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Abstract: | Detailed measurements of the flow instability of dilute shear-thinning viscoelastic aqueous solutions, with relatively low zero-shear viscosities, in an obstructed microchannel flow are reported. We examine the flow behaviour resulting from a 100 μm post placed in the channel centreline over a range of Reynolds numbers (\(5<Re<300\)) and Weissenberg numbers (\(20<Wi<10^3\)). Micro-particle image velocimetry measurements show the onset of an upstream instability within a Reynolds number range and at a critical elasticity number corresponding to polymer concentrations above 25 ppm of long-chain polyacrylamide. The instability results in significant local fluctuations in the flow field approaching 30 % of the mean velocity. The magnitude of the local viscosity ratio in the region upstream of the post is proposed as a driving mechanism for the instability which resembles a buckling flow. Additionally, the classical instability owing to separation and vortex formation downstream of the post in Newtonian flow is suppressed and a very long stable wake is observed extending over 10 post-diameters downstream. |
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