Abstract
This paper reports flow direction-dependent elastic instability in a symmetry-breaking microchannel. The microchannel consisted of a square chamber and a nozzle structure. A viscoelastic polyacrylamide solution was used for the instability demonstration. The instability was realized as the viscoelastic flow became asymmetric and unsteady in the microchannel when the flow exceeded a critical Weissenberg number. The critical Weissenberg number was found to be different for the forward-directed flow and the backward-directed flow in the microchannel.
Highlights
In Newtonian fluid, flow complexity originates mostly from the nontrivial inertial effect, which is mainly induced in the macroscale condition [1]
On the other hand, complex flow behavior can be stimulated from the polymer molecules or surfactant dispersed in the fluid [3,4,5]
In certain designed microchannel structures, the polymer molecules or surfactant can be compressed or stretched to induce significant normal stress in the fluid. Various complex flows such as turbulent flow, Couette flow, or swirling flow can be obtained in viscoelastic fluid even at the micrometer scale [6,7,8,9]
Summary
In Newtonian fluid, flow complexity originates mostly from the nontrivial inertial effect, which is mainly induced in the macroscale condition [1]. On the other hand, complex flow behavior can be stimulated from the polymer molecules or surfactant dispersed in the fluid [3,4,5]. In certain designed microchannel structures, the polymer molecules or surfactant can be compressed or stretched to induce significant normal stress in the fluid. Complex flow can be understood from the Navier–Stokes equation, whereby the nonlinearity of Newtonian fluid depends on the advective term, while viscoelastic fluid nonlinearity is contributed by the rheological effects from the normal stress in the fluid [10], which can be applied for mixing [11,12] or sorting [13] in microfluidics Complex flow can be understood from the Navier–Stokes equation, whereby the nonlinearity of Newtonian fluid depends on the advective term in the equation, while viscoelastic fluid nonlinearity is contributed by the rheological effects from the normal stress in the fluid [10], which can be applied for mixing [11,12] or sorting [13] in microfluidics
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