The influence of rheological properties on the slow flow past spheres

Mena, B.; Manero, Ο.; Leal, L. Gary

doi:10.1016/0377-0257(87)80006-x

Cited by 56 publications

(28 citation statements)

References 24 publications

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“…This suggests that the proposed choice for the typical velocity scale (w i ) and length scale (D), discussed in Section 4, well describes the evolution of the flow pattern observed, at least for low Deborah numbers. This result could be considered as an extension of previous conclusions drawn on the pure settling in non-Newtonian fluid, where the same scaling was adopted and no significant differences with the Newtonian case were detected for De 1 [14,19], although in the present investigation the Reynolds number assumes value much . Note that, after the first rebound, the flow fields have been divided into two subsets (i) earlier time, while the particle is moving upward, (left column) (ii) later time, while the particle is moving downward before impacting a second time (right column).…”

Section: Statistical Description Of the Large-scale Vortical Structuressupporting

confidence: 81%

“…viscoelastic, inelastic, shear thinning), with the purpose of measuring basic quantities, such as the terminal velocity and the drag on the sphere, and of comparing the results with Newtonian experiments, see for example [14][15][16][17][18][19][20]. Recently Stocchino and Guala [13] measured experimentally the coefficient of restitution of a spherical particle impacting a rigid wall immersed in the same viscoelastic shear thinning fluid of the present investigation.…”

Section: Introductionmentioning

confidence: 65%

“…In the literature, most of the work published focused the attention on the pure settling under gravity of a spherical particle inside a cylindrical container [14][15][16][17][18][19][20]. In particular, Mena et al [14] performed a sequence of experiments of particle settling in different fluids (Newtonian, viscoelastic, inelastic and constant viscosity elastic) with the aim to study the influence of the rheological properties on the drag force. Besides, they investigated also the wall effects on the drag force varying the ratio between the particle radius and the radius of the cylindrical container.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Regarding the particle settling in a confined container, it was found that at small Deborah number (De 1) there was no difference with the drag force predicted for a Newtonian fluid [19], which implies that the elasticity of the fluid is irrelevant in that regime. Moreover, Mena et al [14] suggested that the shear thinning behavior can be represented selecting an appropriate Newtonian fluid with a viscosity equal to the non-Newtonian viscosity that corresponds to a rate of strainγ = w s /D, where w s is the terminal velocity. On the contrary, at intermediate values of the Deborah number the elasticity of the fluid begins to affect the sedimentation of the spherical particle and an important drag reduction, higher than 25%, occurs.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…However, neither in the experiments of Gondret et al [10] nor in [13] a velocity decrease was observed, as in the present work. As a representative length scale, we assume the particle diameter D. The choice of the particle diameter D, instead of the thickness of the lubrication layer as in [13], is made in analogy with the case of particle settling in nonNewtonian fluids [14,16,20], even though the present Reynolds numbers are much larger than unity, and in analogy with the scale of the observed flow structures formed during the impact [11,12]. Starting from the selected scales, we obtain a rate of strainγ equal to w i /D as representative for a sphere impacting a wall in a shear thinning fluid.…”

Section: Choice Of a Non-newtonian Fluid And Scaling Argumentmentioning

confidence: 99%

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Large-scale flow structures in particle–wall collision at low Deborah numbers

Guala

Stocchino

2007

European Journal of Mechanics - B/Fluids

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PIV measurements of two dimensional velocity fields during the rebound of a steel spherical particle colliding a wall are provided in Newtonian fluids (distilled water and aqueous solution of Glycerol) and in a viscoelastic shear thinning fluid (aqueous solution of carboxymethyl cellulose). The experiments are designed in order to reproduce the same conditions in which the coefficient of restitution was observed to be significantly affected by viscoelasticity at the typical scales of the lubrication layer [A. Stocchino, M. Guala, Particle-wall collision in shear thinning fluids, Exp. Fluids 65 (2005) 17-46]. In such conditions, the Deborah number, which is a measure of the relevance of the viscoelastic effects compared to the inertial effects, is however relatively low. The aim of the present study is to investigate the relative influence of the elasticity and of the shear thinning character of the nonNewtonian fluid on the large scale flow structures triggered by the particle impact. Special attention is dedicated to the definition of a proper viscosity when the non-Newtonian fluid is involved. In this respect, a scaling argument is suggested to derive the value of the viscosity for an assigned rate of strainγ , given a constitutive law of the kind τ = τ (γ ), where τ is the shear stress. The scaling analysis is supported by previous works on particle settling in non-Newtonian fluids and by recent studies on the flow structures that form as a consequence of a particle-wall collision in Newtonian fluids. The experimental validation of the proposed scaling is provided by first choosing a Newtonian fluid with viscosity equal to the non-Newtonian viscosity and, then, carrying out a comparative analysis of the large-scale vortical structure formed during the collision-rebound process. The statistical analysis suggests that the large scale flow structures observed during the Glycerol experiment and the CMC solution experiment behaves similarly in term of spatial and temporal scales. Therefore, at least for the values of the dimensionless parameters investigated, the shear thinning character of the non-Newtonian fluid employed is dominant with respect of its viscoelasticity.

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Section: Statistical Description Of the Large-scale Vortical Structuressupporting

confidence: 81%

Section: Introductionmentioning

confidence: 65%

Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Choice Of a Non-newtonian Fluid And Scaling Argumentmentioning

confidence: 99%

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Large-scale flow structures in particle–wall collision at low Deborah numbers

Guala

Stocchino

2007

European Journal of Mechanics - B/Fluids

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The conundrum of migraine headaches in the presence of patent foramen ovale

Tobis

2009

Cathet Cardio Intervent

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The accompanying article by the interventional group in Geneva describes their experience in 17 patients who had their PFO closed solely for the indication of severe migraine headaches. This is distinct from most prior observational studies that describe the effect on migraine headache of PFO closure when the procedure was performed primarily to prevent recurrent stroke or decompression illness. Approximately 70% of the patients in this study had a significant decrease or complete abolition (in 24% of cases) of migraine headaches. This current report supplements a recent report by Vigna et al., which describes a positive experience with PFO closure in 53 patients who had migraine headaches and white matter lesions [1]. In that study, the mean number of migraine attacks decreased from 32 to 7 over a 6-month follow up period in the patients who had PFO closure, compared to no significant change in the patients who chose not to have their PFO closed.The observational data obtained from these recent reports, in conjunction with prior observations in cryptogenic stroke patients, is very consistent. Unfortunately, the only randomized controlled trial to date evaluating the effectiveness of PFO closure for migraine headache treatment, the MIST Trial, did not show significant improvement. However, it is believed that a significant proportion of patients in the MIST Trial had a residual shunt after device insertion, likely due to inadequate closure provided by the Starflex device. In addition, the characteristics of the patient population may be different between those included in the MIST Trial and the observational reports, including the present one from Geneva. I hope neurologists consider all the evidence that is currently available and maintain an open position with respect to the association of migraine headaches and patent foramen ovale.There are multiple questions that remain concerning PFO closure and migraine. For instance, we still have not identified which characteristics predict the patients likely to respond to PFO closure. Will the responders include only those with visual aura? Approximately 75% of patients with migraine with aura have a significant benefit from PFO closure, but we have seen about 30% of the patients with migraine without aura who also responded to PFO closure [2]. Are the responders more likely to have transient neurologic deficits (which are frequently misdiagnosed as transient ischemic attacks but actually are complex migraine)? Or should we be concentrating on the patient population that already has evidence of brain involvement; that is, those people with white matter lesions on MRI?Although the majority (60%) of patients screened in the MIST trial had a right to left shunt, there clearly are many people with migraine who do not have a PFO or other etiology of a right to left shunt. In addition, not everyone with a PFO and migraines responds to PFO closure. Nevertheless, as physicians, we are struck by the enormous amount of suffering that patients with frequent migraine must endure. ...

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Flow of non‐newtonian fluids in porous media

Sochi

2010

J Polym Sci B Polym Phys

125

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The study of flow of non‐Newtonian fluids in porous media is very important and serves a wide variety of practical applications in processes such as enhanced oil recovery from underground reservoirs, filtration of polymer solutions and soil remediation through the removal of liquid pollutants. These fluids occur in diverse natural and synthetic forms and can be regarded as the rule rather than the exception. They show very complex strain and time dependent behavior and may have initial yield‐stress. Their common feature is that they do not obey the simple Newtonian relation of proportionality between stress and rate of deformation. Non‐Newtonian fluids are generally classified into three main categories: time‐independent whose strain rate solely depends on the instantaneous stress, time‐dependent whose strain rate is a function of both magnitude and duration of the applied stress and viscoelastic which shows partial elastic recovery on removal of the deforming stress and usually demonstrates both time and strain dependency. In this article, the key aspects of these fluids are reviewed with particular emphasis on single‐phase flow through porous media. The four main approaches for describing the flow in porous media are examined and assessed. These are: continuum models, bundle of tubes models, numerical methods and pore‐scale network modeling. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

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The influence of rheological properties on the slow flow past spheres

Cited by 56 publications

References 24 publications

Large-scale flow structures in particle–wall collision at low Deborah numbers

Large-scale flow structures in particle–wall collision at low Deborah numbers

The conundrum of migraine headaches in the presence of patent foramen ovale

Flow of non‐newtonian fluids in porous media

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