EFFECTS OF FLUID ELASTICITY ON THE STATIC AND DYNAMIC SETTLING OF A SPHERICAL-PARTICLE

The results of an experimental investigation of the settling velocity of spherical particles in viscoelastic fluids are presented. As well a s being fundamentally interesting, this problem is also of relevance t o the understanding of particle transport by well-technology fluids us ed in the oil industry. It is shown that the settling velocity is redu ced by elastic effects in the fluid (e.g., presence of normal stress d ifferences and high elongational viscosity), and that this effect beco mes significantly higher with increasing shear rates experienced by th e falling sphere, i.e. the ratio of settling velocity to sphere diamet er. Imposing an orthogonal shear-flow field on the settling particle c auses a further dramatic reduction of the settling velocity in viscoel astic fluids.