Particle and liquid dispersion in foams

This paper examines the dispersion of particles and liquid through foams. This is of relevance to a wide range of industrial systems in which particles move freely through a foam. In froth flotation, where mineral particles of different types are separated, the dispersion in the froth has a significant impact on the amount and purity of the product obtained. s study, forced drainage experiments were performed with particle pulses added in such a way that the volumetric flow into the foam was not affected. This ensured that the dispersion observed was the result solely of the velocity profile within individual Plateau borders, and not due to the effect of capillary suction on the liquid content in the foam. Experiments were also carried out using a soluble liquid dye as a tracer. cal particle concentration in the foam was measured using light transmission. The particle concentration profiles exhibited near-Gaussian distributions, rather than the sharp rise and decay that would be observed in the case of purely convective dispersion. This confirms that the particles experience a range of velocities as they move through the foam. ateau border dispersion results from the liquid dye experiments were virtually indistinguishable from those for the particles. This shows that the particle dispersion is a direct result of the liquid dispersion, rather than the result of purely particle effects, such as differential settling. clet number was used to characterise the dispersion, as it quantifies the influence of the net convective motion on the dispersion. The Peclet number, using the Plateau border radius of curvature as the characteristic length scale, was found to be constant over a wide range of drainage rates and bubble sizes. For the surfactant system studied in this work, a Peclet number of 0.16 was found. bining the assumption of a constant Peclet number with foam drainage theory, the need to know accurately the bubble size when determining the dispersion coefficient is removed. A 1.5 power law relationship between the dispersion coefficient and liquid velocity was predicted theoretically and confirmed experimentally.