An interpretation of partial plug flow of concentrated suspensions.

The partial plug flow of a concentrated suspension of rigid particles in a circular tube has been previously studied experimentally. It has been shown that a central core may exist in which the mean velocities of the particles and the suspending fluid are equal and constant within a cylindrical core of the flow. This behavior has been attributed to hydrodynamic interaction of the particles within the core. In the present analysis this interaction is interpreted in terms of passing vs. non-passing motions of adjacent particles. A hypothesis of a critical parameter alpha c involving the shear stress and the pressure gradient is explored and a new form of the relation of core diameter to particle size and concentration is developed based on alpha c.