Longitudinal dispersion in mono- and bidisperse foams

Abstract

The dispersion of tracers in draining foams resembles that of porous media, such as dissolved contaminants spreading in soils. Although the latter is of general importance and has received much attention, and dispersion in foams is important for purification and separation processes, there are only a few foam dispersion studies. We developed a technique to measure foam dispersion which is based upon injecting small amounts of a dye, whose concentration profiles resemble δ-functions that quickly evolve into self-similar gaussian distributions. For monodisperse foams our results are in good agreement with Saffman's theory for dispersion in porous media. However for bidisperse foams the dispersion is faster and the concentration profiles are asymmetric.