Particle-wall collision in shear thinning fluids

The present study deals with the measurements of the impact w_i and rebound w_r velocities of steel particles in different fluids colliding with a rigid wall. The results are presented in terms of the coefficient of restitution e=w_r/w_i as a function of the Stokes number (ratio between the particle inertia and the viscous forces). We focus the attention on possible differences between rebounds that occur in Newtonian fluids and in non-Newtonian, shear thinning fluids. The measurements of wet coefficients of restitution in Newtonian fluid are in good agreement with the experimental data found by Gondret et al. (2002). In the range of Stokes number investigated, an increase of the coefficient of restitution with the shear thinning fluid is clearly observed with respect to the Newtonian data. Particular attention has been dedicated to techniques of image processing to perform an optimal estimation of the particle centroid in highly noisy images.