D Guang

Particle settling in oil-in-water emulsions

Abstract 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 ∼10 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.

Residual electrostatic charge and charge distributions on fly ashes produced by the combustion of Australian coals

Electrostatic charges on fly ash particles, measured in situ at several Australian power stations have indicated variations in magnitude and distribution, which can be related to difficulties experienced in cleaning the fabric filters downstream. Measurements made in situ at three Australian power stations, Eraring, Tallawarra and Bayswater showed a considerable variation in charge and distribution with Tallawarra having the largest mean charge (−1.25 μC/g) with a narrow distribution and Eraring having the smallest mean charge (−0.35 μC/g) with a wide distribution. Laboratory tests performed immediately after collection of isokinetic samples from the power stations resulted in lower mean charges (−0.11 μC/g for the Eraring ash) with similar trends in distribution. Further measurements of the charge on the fly ashes taken over several months showed that an inherent charge on the ash particles remains indefinitely (−0.018 μC/g for the Eraring ash and −0.25 μC/g for the Tallawarra ash). It appears that this inherent charge cannot be dissipated by contact with other particles or solid materials.