Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session G10: Non-Newtonian Flows: Rheometry and Applications |
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Chair: Vivek Sharma, University of Illinois - Chicago Room: 110 |
Monday, November 23, 2015 8:00AM - 8:13AM |
G10.00001: Characterizing Printability of Complex Fluids using Dripping-Onto-Substrate Extensional Rheometry Vivek Sharma, Jelena Dinic, Leidy N. Jimenez, Madeleine Biagioli, Alexandro Estrada Liquid transfer and drop formation/deposition processes involved in printing, jetting, spraying and coating involve the formation of columnar necks that undergo spontaneous surface tension-driven instability, thinning and pinch-off. The thinning and pinch-off dynamics are determined by the relative magnitude of capillary forces, and inertial, viscous stresses for simple (Newtonian and inelastic) fluids. Stream-wise velocity gradients that arise within the thinning columnar neck create an extensional flow field, which induces micro-structural changes within complex fluids, contributing extra elastic stresses that change thinning and pinch-off dynamics. Though it is well-established that the quantitative analysis of neck thinning can provide a measure of extensional rheology response and arguably printability, such measurements require bespoke instrumentation not available, or easily replicated, in most laboratories. In this contribution, we describe a method that relies on understanding, visualization and analysis of capillary-driven self-thinning dynamics in an asymmetric liquid bridge formed by dripping a finite volume of fluid from a nozzle onto a substrate. [Preview Abstract] |
Monday, November 23, 2015 8:13AM - 8:26AM |
G10.00002: The importance of flow history in mixed shear and extensional flows Caroline Wagner, Gareth McKinley Many complex fluid flows of experimental and academic interest exhibit mixed kinematics with regions of shear and elongation. Examples include flows through planar hyperbolic contractions in microfluidic devices and through porous media or geometric arrays. Through the introduction of a ``flow-type parameter'' $\alpha$ which varies between 0 in pure shear and 1 in pure elongation, the local velocity fields of all such mixed flows can be concisely characterized. It is tempting to then consider the local stress field and interpret the local state of stress in a complex fluid in terms of shearing or extensional material functions. However, the material response of such fluids exhibit a fading memory of the entire deformation history. We consider a dilute solution of Hookean dumbbells and solve the Oldroyd-B model to obtain analytic expressions for the entire stress field in any arbitrary mixed flow of constant strain rate and flow-type parameter $\alpha$. We then consider a more complex flow for which the shear rate is constant but the flow-type parameter $\alpha$ varies periodically in time (reminiscent of flow through a periodic array or through repeated contractions and expansions). We show that the flow history and kinematic sequencing (in terms of whether the flow was initialized as shearing or extensional) is extremely important in determining the ensuing stress field and rate of dissipated energy in the flow, and can only be ignored in the limit of infinitely slow flow variations. [Preview Abstract] |
Monday, November 23, 2015 8:26AM - 8:39AM |
G10.00003: Physical gelation of a microfiber suspension. Antonio Perazzo, Janine K Nunes, Stefano Guido, Howard A Stone Hydrogels are among the most exploited materials in tissue engineering and there is growing interest in injectable hydrogels, especially as applied to surgical adhesives and bioprinting materials. Here we report a method to produce a hydrogel in a desired location by simply extruding a suspension of high aspect ratio and flexible microfibers from a syringe. The mechanism of gel formation is purely physical and based on irreversible entanglements formed by the microfibers under the action of flow. The single microfibers have been produced and finely tailored by microfluidic methods. Shear rheology has been performed in order to get insights on the entanglements, and results show that the formation of entanglements is related to a shear thickening behavior of the suspension, which in turn depends on shear rate and concentration of fibers. When shearing the suspension, highly non-linear viscoelastic behavior is observed and probed by a highly positive first normal stress difference. We also report the hydrogel swelling behavior and its linear viscoelastic properties as obtained by imposing small oscillatory stress to the material. [Preview Abstract] |
Monday, November 23, 2015 8:39AM - 8:52AM |
G10.00004: Extensional Relaxation Times and Pinch-off Dynamics of Dilute Polymer Solutions Jelena Dinic, Yiran Zhang, Leidy Jimenez, Vivek Sharma We show that visualization and analysis of capillary-driven thinning and pinch-off dynamics of the columnar neck in an asymmetric liquid bridge created by dripping-onto-substrate can be used for characterizing the extensional rheology of complex fluids. Using a particular example of dilute, aqueous PEO solutions, we show the measurement of both the extensional relaxation time and extensional viscosity of weakly elastic, polymeric complex fluids with low shear viscosity $\eta $\textit{ \textless } 20 mPa$\cdot$s and relatively short relaxation time, $\lambda $ \textless 1 ms. Characterization of elastic effects and extensional relaxation times in these dilute solutions is beyond the range measurable in the standard geometries used in commercially available shear and extensional rheometers (including CaBER, capillary breakup extensional rheometer). As the radius of the neck that connects a sessile drop to a nozzle is detected optically, and the extensional response for viscoelastic fluids is characterized by analyzing their elastocapillary self-thinning, we refer to this technique as optically-detected elastocapillary self-thinning dripping-onto-substrate (ODES-DOS) extensional rheometry. [Preview Abstract] |
Monday, November 23, 2015 8:52AM - 9:05AM |
G10.00005: Spray Formation of Herschel--Bulkley Fluids using Impinging Jets Neil Rodrigues, Jian Gao, Jun Chen, Paul E. Sojka The impinging jet spray formation of two non-Newtonian, shear-thinning, Herschel--Bulkley fluids was investigated in this work. The water-based gelled solutions used were 1.0 wt.-{\%} agar and 1.0 wt.-{\%} kappa carrageenan. A rotational rheometer and a capillary viscometer were used to measure the strain-rate dependency of viscosity and the Herschel--Bulkley Extended (HBE) rheological model was used to characterize the shear-thinning behavior. A generalized HBE jet Reynolds number \textit{Re}$_{\mathrm{j,gen-HBE}}$ was used as the primary parameter to characterize the spray formation. A like-on-like impinging jet doublet was used to produce atomization. Shadowgraphs were captured in the plane of the sheet formed by the two jets using a CCD camera with an Nd:YAG laser beam providing the back-illumination. Typical behavior for impinging jet atomization using Newtonian liquids was not generally observed due to the non-Newtonian, viscous properties of the agar and kappa carrageenan gels. Instead various spray patterns were observed depending on \textit{Re}$_{\mathrm{j,gen-HBE}}$. Spray characteristics of maximum instability wavelength and sheet breakup length were extracted from the shadowgraphs. [Preview Abstract] |
Monday, November 23, 2015 9:05AM - 9:18AM |
G10.00006: Phase diagram of vorticity response to surface waviness in viscoelastic Couette flow Jacob Page, Tamer Zaki The response of viscoelastic Couette flow to surface waviness on the lower wall is examined for both Oldroyd-B and FENE-P fluids. The elasticity of the fluid supports vorticity wave propagation along the tensioned streamlines, which results in the formation of a critical layer where the elastic wave speed matches the base velocity. The induced vorticity is quantified using an integral measure of its penetration into the bulk flow. The flow response to the roughness is classified using a phase diagram, analogous to the Newtonian problem (Charru \& Hinch, J. Fluid Mech. 2000). The main parameters in the viscoelastic configuration are the ratios of the channel depth and the critical layer height to the surface wavelength. In deep channels, a significant vorticity is generated away from the wall at the critical layer through a kinematic amplification mechanism. For shallow channels the flow response is dictated by elastic effects, and vorticity amplification occurs in a thin boundary layer at the upper wall. Fourier superposition is used to extend the results to localized wall bumps. Unlike the Newtonian fluid where a single vortex forms above the bump, in the viscoelastic flow an additional upstream vortex of opposite sign is induced by the large vorticity at the upper wall. [Preview Abstract] |
Monday, November 23, 2015 9:18AM - 9:31AM |
G10.00007: Surface textures and Non-Newtonian fluids for decreased friction Jonathon Schuh, Randy Ewoldt Using surface textures has been shown to decrease friction in lubricated sliding contact. A growing trend in the lubrication industry is to add polymers to base oils in order to improve the oil's effectiveness as a lubricant. These polymer additives cause the oil to become a viscoelastic lubricant that will behave differently than a simple Newtonian lubricant. We present an experimental investigation varying both the surface texture depth profile and the viscoelastic lubricant in order to determine their effects on friction reduction. Gap-controlled experiments were performed on a custom tribo-rheometer in order to systematically examine the friction reduction by varying the Reynolds number, Weissenberg number, and Deborah number in bi-directional motion. Cavitation effects are not present so that the normal force is produced solely by the surface textures and the lubricants. We show that the symmetry of the surface textures must be broken in order to produce normal forces above the viscoelastic response, and that an optimal angle of asymmetry $\beta $ exists for decreasing friction with asymmetric surface textures and viscoelastic lubricants. [Preview Abstract] |
Monday, November 23, 2015 9:31AM - 9:44AM |
G10.00008: Experimental and computational fluid dynamic studies of mixing for complex oral health products Marti Cortada Garcia, Luca Mazzei, Panagiota Angeli Mixing high viscous non-Newtonian fluids is common in the consumer health industry. Sometimes this process is empirical and involves many pilot plants trials which are product specific. The first step to study the mixing process is to build on knowledge on the rheology of the fluids involved. In this research a systematic approach is used to validate the rheology of two liquids: glycerol and a gel formed by polyethylene glycol and carbopol. Initially, the constitutive equation is determined which relates the viscosity of the fluids with temperature, shear rate, and concentration. The key variable for the validation is the power required for mixing, which can be obtained both from CFD and experimentally using a stirred tank and impeller of well-defined geometries at different impeller speeds. A good agreement between the two values indicates a successful validation of the rheology and allows the CFD model to be used for the study of mixing in the complex vessel geometries and increased sizes encountered during scale up. [Preview Abstract] |
Monday, November 23, 2015 9:44AM - 9:57AM |
G10.00009: Shape-based Particle Separation via Elasto-Inertia Pinched Flow Fractionation (eiPFF) Xinyu Lu, Xiangchun Xuan We report in this talk a continuous-flow shape-based separation of spherical and peanut-shaped rigid particles of equal volume via elasto-inertial pinched flow fractionation (eiPFF). This separation exploits the shape-dependence of the cross-stream particle migration induced by the elaso-inertial lift force in viscoelastic fluids. The parametric effects on this separation are systematically investigated in terms of dimensionless numbers. It is found that this separation is strongly affected by the Reynolds number, Weissenberg number and channel aspect ratio. Interestingly, the elasto-inertial deflection of peanut particles can be either greater or smaller than that of spherical particles. [Preview Abstract] |
Monday, November 23, 2015 9:57AM - 10:10AM |
G10.00010: Friction factors of colloidal suspension containing silicon dioxide nanoparticles in water Clement Tang, Sarbottam Pant, Md. Tanveer Sharif The purpose of this study is to experimentally characterize the friction factor of a colloidal suspension flow in circular and square tubes. The suspension contained silicon dioxide nanoparticles dispersed in distilled water at 9.58{\%} volume concentration. Rheological measurements indicated that the suspension exhibits non-Newtonian behavior, and could be modelled as a power-law generalized Newtonian fluid. The experimental study showed that, with proper characterization of the consistency and flow behavior indices, the suspension flow friction factors in circular and square tubes exhibit similarities with those of Newtonian fluid flow. In the laminar fully-developed flow region, the Poiseuille numbers are similar to those established for Newtonian fluid flow. In the turbulent region, the Dodge and Metzner relation between the friction factor and a generalized Reynolds number can adequately describe the flow. The onsets of transition to turbulent flow for the suspension vary with the shape of the tube and differ from those of Newtonian fluid flow. The deviations suggest that the flow passage shape and the presence of nanoparticles affect the onset of transition to turbulent flow. [Preview Abstract] |
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