Flow patterns in 4:1 micro-contraction flows of viscoelastic fluids

Abstract

In this paper, the flow pattern of viscoelastic fluids flowing inside a 4:1 planar contraction microchannel was investigated and quantitatively analyzed. A wide range of Weissenberg number flows of poly(ethylene oxide) solutions were observed while maintaining low Reynolds number (0.01 > Re). As the shear rate or fluid elasticity was increased, a transition from steady to unsteady flow was observed. In the steady flow region, the flow pattern was Newtonian-like, progressed to a divergent flow where the upstream flow pattern was distorted due to elasticity, and then a vortex developed at the upstream corners. The vortex, which was stable at first, fluctuated with a certain period as the Weissenberg number increased. The oscillating vortex was symmetric at first and became asymmetric with various patterns. As the elasticity increased further, the vortex randomly fluctuated without any time period. The Lyapunov exponent for the change in vortex size was positive, meaning that the flow was spatially chaotic. This paper systematically analyzed the flow patterns of the elastic fluids in the micro-contraction flow, which included; Newtonian-like flow, divergent flow, oscillating flow with symmetry, oscillating flow with asymmetry, and chaotic flow.

Vortex behavior of particle suspension flow in a wedge for the second-order fluid

“…Therefore, we can conclude that increase of the flow rate enhances the vortex length, which is the same as that given by Kim et al [22]. The vortex length increases with the increase of We, which is consistent with the results given by Ferrás et al's numerical simulation [24] and Lee and Ahn's experiment [25] for viscoelastic fluids in a 4:1 contraction. Actually the fact that the vortex length is larger for larger We is related to the larger extensional viscosity that increases the fluid flow resistance, and consequently, a larger portion of fluid recirculates, creating larger vortices.…”

Effect of Colloidal Interactions and Hydrodynamic Stress on Particle Deposition in a Single Micropore

“…Material processing can be understood as the “transport phenomena of complex fluid” in a wide range of industries such as petrochemicals, semiconductors, batteries, biotechnology, and pharmaceuticals. In these processes, materials flow through various confined geometries such as pipes, nozzles, filters, and membranes. − A colloidal suspension flowing in such a confined geometry often causes clogging, which is an undesirable phenomenon because it degrades process performance and causes various flow problems (e.g., unpredictable deformation of the flow field, increased residence time, and vortex formation) . To understand the clogging mechanism, microfluidics has been widely employed in previous studies because the operational conditions (e.g., geometrical parameters or flow conditions) are easily controlled, and direct observations of clogging dynamics are possible …”