THE INFLUENCE OF SURFACE-ROUGHNESS ON THE PARTICLE-PAIR DISTRIBUTION FUNCTION OF DILUTE SUSPENSIONS OF NON-COLLOIDAL SPHERES IN SIMPLE SHEAR-FLOW

The pair distribution function of 3.18 mm diameter particles was measu red in the plane of shear of a simple shear flow at concentrations of 5%, 10% and 15% by volume. A new direct flow-visualization procedure a nd a new pattern recognition algorithm were used in the investigation. The measurements show a depletion of bound pairs of particles in the direction of how. A simple model which includes the effect of particle surface roughness on the particle interactions and the pair distribut ion function is presented. An important effect of surface roughness is that the particles in a suspension can experience irreversible intera ctions in the presence of an externally imposed simple shear flow. The model shows that such irreversibilities eliminate all bound pairs of particles in the plane of shear by displacing particles out of the clo sed orbit trajectory region. Surface roughness is found to induce sign ificant asymmetry in the fore and aft region of a two-particle interac tion. The measurements and predictions are in qualitative agreement wi th these conclusions.