Particle settling in oil-in-water emulsions

The sedimentation velocity of precision steel spheres in several oil-in-water emulsions stabilized by a range of commercially available surfactants has been measured. in particular, the interaction between the size distribution of oil droplets, the viscosity of emulsions and the terminal velocity of spheres has been investigated in the Reynolds number range similar to 10 to similar to 1000. When the oil droplets are much smaller than the size of the sedimenting particle, one can treat the emulsion as a continuum fluid and available frameworks can be used for the estimation of the settling velocity. However, the accuracy of this so-called 'continuum' approximation is likely to deteriorate rapidly with increasing droplet size and/or decreasing size of the sedimenting particles. (C) 1998 Elsevier Science S.A. All rights reserved.