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

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

Prediction of extrusion load and liquid phase filtration during ram extrusion of high solid volume fraction pastes

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

The method involves moisturizing and coating a solid (4) e.g. expanded clay, in respective rotation states (2, 3). The solid is sieved before coating and before and/or during moisturizing the solid. The sieving of the solid takes place for removing fine parts such that formation of secondary granulates and cement parts is reduced. A large amount of water is sprayed on the solid for moisturizing the solid. The moisturizing of the solid takes place on a rotary inclined plate i.e. granulate plate. An additive e.g. calcium hydroxide rich material, is added during coating of the solid. An independent claim is also included for a device for coating a solid.

Method and device for encasing solids

Die Erfindung betrifft ein Verfahren zur Feststoffumhullung, worin ein Feststoff rotierend befeuchtet und umhullt wird. Hierbei ist vorgesehen, dass der Feststoff in einer ersten Rotationsstufe befeuchtet, ausgetragen und in einer zweiten Rotationsstufe umhullt wird.

Marian Prof. Dr.-Ing. Peciar

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

Method and device for encasing solids

Verfahren und Vorrichtung zur Feststoffumhüllung