# X Radiography of Viscous Resuspension

## TL;DR

This study employs X-ray imaging to analyze viscous resuspension in a Taylor-Couette setup, revealing nonlinear particle stress behaviors and shear-thinning effects in semi-dilute suspensions, challenging existing theories.

## Contribution

It provides new experimental data on particle stress and viscosity in semi-dilute suspensions, highlighting nonlinear and shear-dependent behaviors not previously documented.

## Key findings

- Particle stress is quadratic with volume fraction in dilute limit
- Nonlinear dependence of stress on Shields number observed
- Evidence of shear-thinning and non-Coulomb friction between particles

## Abstract

We use X-ray imaging to study viscous resuspension. In a Taylor-Couette geometry, we shear an initially settled layer of spherical glass particles immersed in a Newtonian fluid and measure the local volume fraction profiles. In this configuration, the steady-state profiles are simply related to the normal viscosity defined in the framework of the Suspension Balance Model (SBM). These experiments allow us to examine this fundamental quantity over a wide range of volume fractions, in particular in the semi-dilute regime where experimental data are sorely lacking. Our measurements unambiguously show that the particle stress is quadratic with respect to the volume fraction in the dilute limit. Strikingly, they also reveal a nonlinear dependence on the Shields number, in contrast with previous theoretical and experimental results. This likely points to shear-thinning particle stresses and to a non-Coulomb or velocity-weakening friction between the particles, as also evidenced from shear reversal experiments.