18 articles – 54 Notices  [english version]
 HAL : hal-00507429, version 2
 arXiv : 1007.5446
 DOI : 10.1122/1.3526349
 Journal of Rheology / Transactions of the Society of Rheology; Society of Rheology -- Transactions 55 (2011) 197-223
 Versions disponibles : v1 (30-07-2010) v2 (03-05-2011)
 Flows and heterogeneities with a vane tool: Magnetic resonance imaging measurements
 (2011)
 We study the local flow properties of various materials in a vane-in-cup geometry. We use magnetic resonance imaging techniques to measure velocities and particle concentrations in flowing Newtonian fluid, yield stress fluid, and in a concentrated suspension of noncolloidal particles in a yield stress fluid. In the Newtonian fluid, we observe that the $\theta$-averaged strain rate component $d_{r,\theta}$ decreases as the inverse squared radius in the gap, in agreement with a Couette analogy. This allows direct comparison (without end-effect corrections) of the resistances to shear in vane and Couette geometries. Here, the mean shear stress in the vane-in-cup geometry is slightly lower than in a Couette cell of same dimensions, and a little higher than when the vane is embedded in an infinite medium. We also observe that the flow enters deeply the region between the blades, leading to significant extensional flow. In the yield stress fluid, in contrast with the usually accepted picture based on simulation results from the literature, we find that the layer of material that is sheared near the blades at low velocity is not cylindrical. There is thus a significant extensional component of shear that should be taken into account in the analysis. Finally and surprisingly, in the suspension, we observe that a thin non-cylindrical slip layer made of the pure interstitial yield stress fluid appears quickly at the interface between the sheared material and the material that moves as a rigid body between the blades. This feature can be attributed to the non-symmetric trajectories of the noncolloidal particles around the edges of the blades. This new important observation is in sharp contradiction with the common belief that the vane tool prevents slippage and may preclude the use of the vane tool for studying the flows of pasty materials with large particles.
 1 : Laboratoire Navier Ecole des Ponts ParisTech – CNRS : UMR8205 – IFSTTAR
 Équipe de recherche : RhéophysiqueMilieux poreux
 Domaine : Physique/Matière Condensée/Matière Molle
 Mots Clés : Vane tool – MRI – Yield stress – Migration – Suspension
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 Ovarlez_vane_tool_MRI_v2.pdf(1.1 MB)
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 Ovarlez_vane_tool_MRI_v2.ps(10.1 MB)
 hal-00507429, version 2 http://hal.archives-ouvertes.fr/hal-00507429 oai:hal.archives-ouvertes.fr:hal-00507429 Contributeur : Guillaume Ovarlez <> Soumis le : Lundi 2 Mai 2011, 15:53:37 Dernière modification le : Mardi 3 Mai 2011, 09:01:19