This study investigates the effects of yield stress and shear banding on the fluidic behaviors of cetyltrimethylammonium bromide/sodium salicylate wormlike micellar solutions flowing through a microfluidic planar contraction (8:1) geometry. Test solutions with different surfactant concentrations (Cd = 75, 87.5, and 100 mM) at a fixed molar ratio of salt to surfactant (R=0.32) were characterized by shear and extensional rheometry. While the lower concentrated test solution (Cd = 75mM) with low (≈ 0.02Pa) and no shear banding showed a Newtonian-like flow behavior for Mach number, Ma<1, the flow with corner vortices was formed when Ma exceeds unity. For higher Cd (87.5 and 100mM), new fluidic phenomena are documented: (i) even at a low volumetric flow rate (Q), the fluid velocity at upstream corners was slower than that of Newtonian-like flows and (ii) at higher Q, the secondary flow with a quasi-static condition was formed at Ma well lower than unity. Micro-particle image velocimetry showed the lower shear rates at upstream corners, which can be understood by the effects of contraction entry, shear thinning, and high yield stress. The quasi-static secondary flow region was not induced by generation of elastic shock waves; instead the shear banding was found to be the underlying mechanism for the separation of the region from the main flow. In addition, the length of secondary flow regions showed a close correlation with the Deborah number, which was calculated using the extensional relaxation time.
|Journal||Physics of Fluids|
|Publication status||Published - 2021 Sept 1|
Bibliographical noteFunding Information:
The authors would like to acknowledge the financial support from the Donors of the American Chemical Society Petroleum Research Fund (ACS-PRF 57552-ND9), the Brain Pool Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2020H1D3A2A01041079 and 2021H1D3A2A01045033), and the International Research Accelerator program at Texas State University. The authors declare there are no conflicts of interest.
© 2021 Author(s).
All Science Journal Classification (ASJC) codes
- Computational Mechanics
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
- Fluid Flow and Transfer Processes