Studies of the Coalescence of Dispersions in Particulate Packings

Abstract

Droplet hydrodynamics and coalescence mechanisms in a packed bed have been studied using a mono-sized primary inlet dispersion with a packing of equal sized glass spheres. Four systems were studied and a correlation was developed using a dimensional analysis to evaluate the parameters affecting the exit drop size of a packed bed. A technique was developed to evaluate the mean exit drop size by producing a Shadowgraph capable of automatic analysis on an Image Analysing Computer. Two distinct processes of droplet behaviour were identified within a packed bed. In the first, droplets entered and passed through the packing until they met a restriction, at which droplet retention and subsequent coalescence occurred. The second process was drop formation at the exit of the packing, which was related to the release mechanisms which occurred after the retained droplets had grown by coalescence. A mathematical model was developed to relate the buoyancy and surface forces in, terms of the drop size and shape in the aperture of a packing element. The model can be used to predict the range of drop diameters that will not pass through a packing restriction. The lower and upper limits refer to the initial point of drop retention and the eventual Point of drop release, and this has been related to the geometry of the packing within the bulk of the bed and in the exit layer respectively. Good agreement was found between predicted and experimental values for both simulated single packing restrictions and packed beds. A definition of a packing efficiency. has been proposed by equating the experimental mean exit drop size with the theory of droplet release and the probability of droplet retention. This has enabled a quantitative comparison to be made of the theoretical and experimental limitations of a packed bed as a coalescing aid.