Concentration and velocity measurements in non-Brownian suspensions using ultrasonic imaging

We investigate the sedimentation and the re-suspension of dense, non-Brownian particles using ultrasonic imaging in a Couette cell, coupled to rheological measurements. Our setup records the characteristic speckle signal – originating from the multitude of particles (PS, PMMA, glass) in the Couette cell scattering an initial ultrasound pulse – on a transducer array. This “speckle map” can be used to estimate the velocity field and the particle concentration in our cell. We will discuss the advantages and limitations of our device using canonical examples when the suspending fluid is Newtonian: viscous re-suspension, sedimentation, particle migration by centrifugal forces and in Taylor vortices. Finally, some results involving non-Newtonian suspending fluids will be presented.