Viscosity scaling in suspensions of non-Brownian rodlike particles

A systematic experimental study of the settling of a spherical ball in a fiber suspension for different particle aspect ratios and a wide range of volume concentrations is presented. The situation where the ball size is much greater than the fiber length is considered. First, it has been observed that, even at very low concentration, the flow induced by the sphere drastically modifies rile orientation distribution of the particles. It was found that, in the dilute and semidilute regime, the viscosity inferred from the sphere falling velocity scales with the excluded volume and compares well with existing shear measurements. Moreover, the viscosity was found to be almost independent of the initial orientation distribution of the fibers, indicating that the rheological response of the suspension was dominated by the configuration induced by the sphere displacement. (C) 1997 American Institute of Physics. [S1070-6631(97)00412-1].