Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session U13: Microscale Flows: Non-Newtonian Fluids (8:45am - 9:30am CST)Interactive On Demand
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U13.00001: Hydrodynamic Performance of Non-Newtonian Viscoelastic Fluid Flow in a Microhannel with Multiple Contractions Ali Zargartalebi, Mohammad Zargartalebi, Anne Benneker The behavior of a viscoelastic fluid through small channels is relevant for applications in medicine, oil recovery and polymer processing. In this work, we numerically study a shear-thinning viscoelastic fluid through a channel with contractions. We express viscoelastic features using an Oldroyd-B model and describe the non-Newtonian behavior with the Carreau model. Parameters effecting the performance of these fluids including local stress, pressure and velocity were examined in channels with single and multiple contractions. While the influence of the non-Newtonian behavior is small, the effect of elasticity is significant. With increasing elasticity, the stresses around the contraction become more pronounced and the formation of dead zones is suppressed. When analyzing multiple consecutive contractions we observe memory-like behavior of the fluid where the local stress decreases in downstream contractions. Finally, we find that with increasing channel size, the influence of elasticity on the local stresses and fluid flow behavior in the channel becomes insignificant. These results are relevant for systems in which local stresses should be optimized and indicate that by tweaking the elasticity of the fluid the behavior of the system can be controlled. [Preview Abstract] |
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U13.00002: Propulsion of magnetically actuated achiral swimmers in complex fluids. Zhi Chen, Zihan Wang, David Quashie, Prateek Benhal1, Jamel Ali, U Kei Cheang Recently reported achiral microswimmers can be massively fabricated at low cost and are envisioned for used in future in vivo biomedical applications, such as drug delivery and minimally invasive surgeries. Towards this goal, we report on the propulsion of two-dimensional magnetic microswimmers, fabricated through photolithography, and actuated in dilute methylcellulose solutions. We observed that the microswimmers displayed increased swimming speeds in certain polymer concentrations. Furthermore, we observed that the reduction rate of achiral microswimmers' precession angle increases with the concentration of the polymer weight percent. Upon understanding the underlying principles, more effective control strategies can be implemented on achiral microswimmers to perform biomedical tasks. These observations suggest that achiral microswimmers have similar speed enhancement to those well known to exist for chiral simmers in complex media. [Preview Abstract] |
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U13.00003: Heat and Mass Transfer in Oscillatory Squeeze Flow of a Maxwell Fluid Rui Yang, Ivan Christov, Ian Griffiths, Guy Ramon Taylor--Aris dispersion occurs in periodically driven flows, due to the interactions of out-of-phase velocity and temperature/concentration gradients. We study the scalar transport in an oscillatory axisymmetric squeeze flow of a Maxwell fluid, driven periodically by the motion of one of the confining, parallel planes. Using multiple-scales homogenization, we derive a one-dimensional advection--diffusion--reaction equation. The homogenized equation shows that time-averaged transport can be understood as a combination of three effective mechanisms: diffusion, advection and reaction. We discover that the effective diffusion always helps transport, and it can be sharply enhanced when the dimensionless plate oscillation frequency (specifically, the Womersley number, which is the ratio of the transient inertial to the viscous forces) approaches a resonant value, at which the velocity amplitude peaks. However, the effective advection and reaction mechanisms may carry heat/mass from low-temperature/concentration regions to high-temperature/concentration regions, or vice versa, depending on the Womersley, the Prandtl/Schmidt and the Deborah numbers. We show that the interplay of these effective mechanisms determines whether the transport is enhanced or diminished. [Preview Abstract] |
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U13.00004: Surfactant effects on microfluidic contraction and expansion flows. Michael Dacus, Sean Hekker, Mahmud Raihan, Xiangchun Xuan Sorting particles is critical in many applications such as environment monitoring, food safety, and water quality control. Over the past decade, there has been a rapidly growing interest in the use of flow-induced lift forces to focus and separate particles in both Newtonian and non-Newtonian fluids through microchannels. Surfactants like tween 20 are often mixed into the particle suspensions to minimize particle aggregation and adhesion issues. It is, however, unknown if the addition of surfactants has an impact on the fluid and particle motions. We present in this talk an experimental study of the flow of deionized water and shear-thinning xanthan gum solution through a planar expansion-contraction microchannel. The flow pattern is visualized via the use of small tracing particles seeded in each solution both with and without the surfactant. The comparison of the vortex development is performed in a similar wide range of flow rates. [Preview Abstract] |
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U13.00005: Modeling and simulating transient flows of thixotropic and viscoelastic fluids in microfluidic tubes Soham Jariwala, Tim Van de Vyver, Norman Wagner, Antony Beris An efficient methodology is developed for numerical simulation of flows in tubular geometries using a pseudo-spectral method based on Chebyshev basis. The proposed basis minimizes the truncation error as one can reach machine precision in fewer terms when the solution is expressed as an expansion of Chebyshev polynomials. The model follows, with high fidelity, the analytical solution of Newtonian and Maxwell fluids in oscillatory pressure-driven flows. The methodology can be useful in simulating highly non-linear velocity and shear stress profiles observed during transient flows of complex fluids in microchannels with arbitrary pressure forcing. This is demonstrated using existing elasto-viscoplastic fluid models, such as the one derived by Stephanou and Georgiou (J. Chem. Phys. 149, 244902, 2018) for thixotropic systems from non-equilibrium thermodynamics. The time and shear history dependence as well as the flow induced breakdown and buildup of the fluid microstructure is captured in a scalar field variable. [Preview Abstract] |
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