Sedimentation of a rotating sphere in a power-law fluid

• We study the sedimentation of spheres in an inelastic shear-thinning fluid.
• The spheres are also rotated around their sedimentation axis.
• The rotation causes an increase of the sedimentation speed.
• This setup can be used as a new type of rheometer for shear-dependent fluids.

We measure the sedimenting velocity of rigid spheres in power-law fluids. By imposing a controlled rotation, we can increase the typical shear rate in the surrounding fluid leading to a decrease of the effective fluid viscosity and, consequently, an increase of the sedimentation speed of the spheres. By fitting our experimental measurements to a power-law dependence of the sedimentation speed on the rotation frequency we are able to predict the values of the consistency and power indices for the test fluids. This setup could thus be used as a rheometer for power-law fluids.