Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session M11: Non-Newtonian Flows II |
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Chair: Sarah Kieweg, University of Kansas Room: 335 |
Tuesday, November 26, 2013 8:00AM - 8:13AM |
M11.00001: Electrokinetic particle motions in non-Newtonian fluids through a microchannel contraction Xinyu Lu, Sang-Woo Joo, Shizhi Qian, Xiangchun Xuan Electrokinetic flow is a powerful means to transport and control fluids and particles in microfluidic devices. To date, however, nearly all previous studies have used aqueous buffer solutions that are Newtonian fluids. We present our recent experimental results of the electrokinetic particle motions in a phosphate buffer with (which is a non-Newtonian fluid) and without (which is a Newtonian fluid) the addition of polyethylene oxide (PEO) through a planar contraction-expansion microchannel. We find that the viscoelasticity of the PEO solution can cause a particle bouncing phenomenon in the contraction, which has never been observed in Newtonian fluids. The effects of electric field, particle size, PEO concentration, and buffer concentration on this electrokinetic particle instability are experimentally examined. [Preview Abstract] |
Tuesday, November 26, 2013 8:13AM - 8:26AM |
M11.00002: Reversibility and Chaos in Microscopic Fluid Systems Liat Rosenfeld, Lin Fan, Sindy K.Y. Tang In this study, we explore the transition from reversible to chaotic behavior in an oscillatory shear flow of water-in-oil emulsions. Emulsions are complex materials and have many applications in chemical, biological and industrial processes. The many-body, shear-history-dependent nature of the microstructure renders the prediction of the complex material's dynamics and rheology highly nontrivial. The emulsion was injected through a microchannel and was forced to rearrange due to a central constriction in the channel. We study the motion of the individual droplets and their neighbors in order to determine their ability to retain their original position after several cycles of oscillations. We have found that while at the Stokes flow limit, the emulsion exhibit behaviors that vary from complete reversibility to complete irreversibility depending on the volume fraction, velocity and strain rate. We provide the first direct visualization of this phenomenon. This work is an important step in understanding the microscopic rearrangements of droplets and particles near jamming. [Preview Abstract] |
Tuesday, November 26, 2013 8:26AM - 8:39AM |
M11.00003: A Computational Study of Viscoelastic Effects on Drop Dynamics in Microchannels Daulet Izbassarov, Metin Muradoglu A front-tracking method is developed and applied to study effects of viscoelasticity on drop dynamics in microchannels. The FENE-CR and Oldroyd-B models are employed to model the viscoelasticity. The viscoelastic model equations are solved fully coupled with the flow equations. An explicit semi-analytical time integration scheme is used for the viscoelastic model equations at low Deborah numbers and a log-conformation is used to alleviate the well-known difficulties at high Deborah numbers. The log-conformation is found to be stable and very robust for a wide range of Deborah numbers. The method is first validated for the benchmark single-phase viscoelastic flow through an axisymmetric channel with a 4:1 constriction and the results are found to be in a good agreement with earlier computational simulations. The algorithm is then used to study fluid dynamics of buoyancy-driven viscoelastic two-phase systems in a capillary tube. Extensive computations are performed to examine the effects of confinement and rheological properties of the phases on drop mobility and deformation. Finally, the method is applied to study the motion and deformation of a viscoelastic droplet in a pressure driven axisymmetric contraction/expansion micro-channel. Key Words:Viscoelastic fluid,FENE model. [Preview Abstract] |
Tuesday, November 26, 2013 8:39AM - 8:52AM |
M11.00004: Falling Film Flow of Slag Ling Miao, Wei-Tao Wu, Nadine Aubry, Mehrdad Massoudi In this paper, numerical calculations have been performed to study the heat transfer in the fully developed flow of a slag layer down a vertical wall. A new constitutive relation for the stress tensor of the slag is proposed, where the viscosity depends on the volume fraction, temperature, and shear rate. For the heat flux vector, we assume the Fourier's law of conduction with a constant thermal conductivity. The model is also capable of exhibiting normal-stress effects. The effects of various dimensionless numbers on the velocity, temperature and volume fraction are examined by numerically solving the governing equations. We also compared the different cases of shear thinning and shear thickening, cooling and heating. The effect of the exponent in the Reynolds viscosity model is also discussed. The results indicate that the viscous dissipation and radiation (at the free surface) cause the temperature to be higher inside the flow domain. [Preview Abstract] |
Tuesday, November 26, 2013 8:52AM - 9:05AM |
M11.00005: Modeling flow of nematic liquid crystal down an incline Michael Lam, Linda Cummings, Te-Sheng Lin, Lou Kondic The flow of nematic liquid crystals (NLCs) down an inclined substrate is studied. Under the usual long wave approximation, a 4th order nonlinear parabolic partial differential equation (PDE) of diffusion type is derived for the free surface height, $z = h(x, y, t$). The model accounts for elastic distortions of the director field due to different anchoring conditions at the substrate and the free surface. The PDE we derive admits 2D traveling-wave solutions, which may translate stably or exhibit instabilities in the flat film behind the traveling front. These instabilities, which are distinct from the usual transverse instability of downslope flow, may be analyzed and explained by linear stability analysis of a flat translating film. Intriguing parallels are found with the instabilities exhibited by Newtonian fluid flowing on an inverted substrate [T-S. Lin and L. Kondic, Phys. Fluids \textbf{22}, 052105 1-10, (2010)]. [Preview Abstract] |
Tuesday, November 26, 2013 9:05AM - 9:18AM |
M11.00006: Influence of yield stress and shear thinning on the capillary ridge formation of gravity-driven Herschel-Bulkley fluid on an incline Md. Rajib Anwar, Bin Hu, Kyle Camarda, Sarah Kieweg In this work on gravity-driven spreading, we discuss the impact of surface tension on the spreading and free surface shape of a finite bolus of a Herschel-Bulkley fluid. We incorporate surface tension into a 2D (i.e. 1D spreading) Herschel-Bulkley thin film flow model. Studies have indicated that incorporating surface tension can result in the emergence of a capillary ridge in thin fluid films and the capillary ridge is strongly related to contact line fingering instability. Our previous numerical study showed that increased shear-thinning (in a fluid without yield stress) suppressed the capillary ridge. A previous linear stability analysis by Balmforth \textit{et al}. (2007) showed that the yield stress in a Bingham fluid dampens the instability. Our numerical results in this study will provide initial insight on the impact of yield strength, shear-thinning index, and inclination angle on the overall spreading and appearance of the capillary ridge in Herschel-Bulkley fluids. [Preview Abstract] |
Tuesday, November 26, 2013 9:18AM - 9:31AM |
M11.00007: The effect of the polymer relaxation time on the nonlinear energy cas- cade and dissipation of statistically steady and decaying homogeneous isotropic turbulence Pedro C. Valente, Carlos B. da Silva, Fernando T. Pinho We report a numerical study of statistically steady and decaying turbulence of FENE-P fluids for varying polymer relaxation times ranging from the Kolmogorov dissipation time-scale to the eddy turnover time. The total turbulent kinetic energy dissipation is shown to increase with the polymer relaxation time in both steady and decaying turbulence, implying a ``drag increase.'' If the total power input in the statistically steady case is kept equal in the Newtonian and the viscoelastic simulations the increase in the turbulence-polymer energy transfer naturally lead to the previously reported depletion of the Newtonian, but not the overall, kinetic energy dissipation. The modifications to the nonlinear energy cascade with varying Deborah/Weissenberg numbers are quantified and their origins investigated. [Preview Abstract] |
Tuesday, November 26, 2013 9:31AM - 9:44AM |
M11.00008: Chemically-reacting non-linear fluid with variable transport properties Kerem Uguz, Mehrdad Massoudi We study the momentum and the heat transfer of a chemically reacting non-linear fluid between two long horizontal plates which are kept at constant but different temperatures. The top plate is sheared at constant speed, while the bottom plate is kept stationary. The physical parameters of the fluid, i.e. the viscosity, the thermal conductivity and the diffusion coefficient are assumed to be a function of the concentration. The boundary value problem is solved numerically using Chebyshev Spectral Method. A detailed parametric study of the velocity, the temperature, and the concentration profiles are presented for shear-thinning/thickening and chemically-thinning/thickening fluids. [Preview Abstract] |
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