SEDIMENTATION OF SOLID PARTICLES IN OIL-IN-WATER EMULSIONS

This study reports experimental results on the sedimentation of spherical glass beads in oil-in-water emulsions. The oil droplets had a volume/surface mean diameter of about 10 mum. Three different sizes of glass beads were used, namely, 29, 57 and 157 mum. The solids volume fraction, based on the total volume, was varied up to 0.4; and the oil volume concentration, solids free basis, was varied up to 40%. The fingering phenomenon was observed for the case of the small solids of 29 mum. As a result, both the settling velocity of the solids and the creaming velocity of the oil droplets were significantly enhanced. For the case of the intermediate solids (57 mum), no fingering was observed when the solids settled in a 20% oil emulsion. The settling velocity of the solids can be predicted by assuming the emulsion to form a continuous phase. However, fingering was observed when the solids settled in a more concentrated (40%) emulsion. For the case of the large solids (157 mum), no structure of any kind was observed. The solids settling velocity can be predicted by assuming the emulsions to form a continuous phase. For the low oil concentration (20%) emulsion system, the conditions for the onset of internal structures (fingering) for the different solids were consistent with previous experimental observations for the case of bidisperse solids suspensions.