• Richter, Sébastien Kiesgen De
• Louvet, Nicolas
• Gaudel, Naïma
• Ferrari, Maude
• Jenny, Mathieu

Abstract

Local rheometry of non-Brownian fibers suspensions is investigated using both classical rheometry and MRI measurements in a cylindrical Couette configuration (fig. 1 left). It allows us to extract the local and the global rheometry for different applied shear rates and volume fraction φ. We observed a localized flow. The fluid/solid interface position depends on φ and the shear rate ˙ γ. We discuss the irreversible behavior of the flow. Near the jamming transition, we observe that the suspension becomes like a yield stress fluid. Nevertheless , an irreversible destructuring behavior is put in evidence (fig. 1. right). Our data can be well fitted to a Hershel-Bulkley law. We discuss the evolution of the consistency, the shear-thinning index and the yield stress with the volume fraction of the suspension. Models using a structural parameter, such as Houska's model [1] or Mills' model [2] use a kinetic equation for the structural parameter which implies reversible destructuring flows. For exemple, Houska's model, used for waxy crud oils, can not reproduce irreversible behavior in flows with a complex history [3-4]. New kinetic for the structural parameter should be proposed to take into account irreversible flows. 0.008 0.009 0.01 0.011 0.012 0.013 0.014 0.015 Radial position (m) 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 Velocity (m/s) 6rpm (up) 9rpm (up) 15rpm (up) 21rpm (up) 15rpm (down) 9rpm (down) 6rpm (down) Figure 1: Couette setup and MRI velocity profiles in fibers suspension (mass ratio 24.7/120, i.e. φ =?). Full and dashed lines stand for growing and decreasing steps of velocity.

Topics

• impedance spectroscopy
• rheometry