We investigate the flowing behavior of dense suspensions of noncolloidal particles, by coupling macroscopic rheometric experiments and local velocity and concentration measurements through magnetic resonance imaging (MRI) techniques. We find that the flow is localized at low velocities, and that the material is inhomogeneous; the local laws inferred from macroscopic rheometric observations must then be reinterpreted in light of these local observations. We show that the short time response to a velocity step allows dense suspensions to be characterized locally: they have a purely viscous behavior, without any observable influence of granular friction. In the “jammed” zone, there may be a contact network, whereas in the sheared zone there are only hydrodynamic interactions: localization consists of a change in configuration at the grain scale. From the concentration and velocity profiles, we provide for the first time local measurements of the concentration dependence of viscosity, and find a Krieger-Dough...

https://hal.archives-ouvertes.fr/hal-00776443/document

Local determination of the constitutive law of a dense suspension of noncolloidal particles through magnetic resonance imaging

https://pureadmin.qub.ac.uk/ws/files/120688801/Cements1_s2.0_S1742706116306067_main.pdf

Critical review: Injectability of calcium phosphate pastes and cements.

Dynamic MRI in chemical process and reaction engineering

We propose in this work to provide an efficient and simple extruder device able to evaluate the rheological and tribological behaviour of high yield stress fluids, such as extrudible materials. An extruder able to measure simultaneously both the friction force acting on the extruder wall and the total extrusion force is developed. Based on previous studies, an efficient and accurate method of data analysis is then proposed and applied in order to obtain both a flow curve and a tribological law. Experimental tests are performed on soft modelling clay, kaolin paste and cement-based materials. Results are compared to conventional rheometry measurements. This comparison helps to evaluate the accuracy of the proposed experimental device and procedure.

/pdf/use-of-ram-extruder-as-a-combined-rheo-tribometer-to-study-3e89d1rprd.pdf

Use of ram extruder as a combined rheo-tribometer to study the behaviour of high yield stress fluids at low strain rate

An analysis of the yielding and flow behavior of a model yield-stress fluid, 0.2 wt% Carbopol gel, in a capillary with slip at the wall has been carried out in the present work. For this, a study of the flow kinematics in a capillary rheometer was performed with a two-dimensional particle image velocimetry (PIV) system. Besides, a stress-controlled rotational rheometer with a vane rotor was used as an independent way to measure the yield stress. The results in this work show that in the limit of resolution of the PIV technique, the flow behavior agrees with the existence of a yield stress, but there is a smooth solid–liquid transition in the capillary flow curve, which complicates the determination of the yield stress from rheometrical data. This complication, however, is overcome by using the solely velocity profiles and the measured wall shear stresses, from which the yield-stress value is reliably determined. The main details of the kinematics in the presence of slip were all captured during the experiments, namely, a purely plug flow before yielding, the solid–liquid transition, as well as the behavior under flow, respectively. Finally, it was found that the slip velocity increases in a power-law way with the shear stress.

https://www.repositoriodigital.ipn.mx/bitstream/123456789/13199/1/Articulo%208-2012.pdf

Rheo-PIV of a yield-stress fluid in a capillary with slip at the wall

Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The 19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by means of correlation techniques without any preparation or marking of the pastes.

Extrusion of pastes with a piston extruder for the determination of the local solid and fluid concentration, the local porosity and saturation and displacement profiles by means of NMR imaging

In this paper, the spatially resolved determination of velocities in suspensions by means of nuclear magnetic resonance (NMR) imaging (MRI) techniques is described and applied to steady tube flows (with regard to the total flow rate) in different geometries. Three types of suspensions with different solid volume concentrations are examined in order to demonstrate the influence of the material-specific flow-behaviour and of the geometry of the experimental set-up on the observed flow-pattern. MRI offers the possibility to study the flow of multiphase materials with various forms of contrast (e.g. spin density, relaxation and spectroscopic data, diffusive and convective transport) spatially resolved. Thus even optically opaque suspensions can be studied in the interior of the material and the studied device. In this work the local probability distribution of single velocity components is determined. From this probability distribution both the local mean value and the according standard deviation can be derived. The standard deviation can be interpreted as the local dispersion coefficient of the according velocity component.

Wolfgang Kreibich

Papers

Extrusion of pastes with a piston extruder for the determination of the local solid and fluid concentration, the local porosity and saturation and displacement profiles by means of NMR imaging

Possible optimisation of pastes and the according apparatus in process engineering by MRI flow experiments