A rheological model for a liquid-gas foam

The flow of a liquid-gas foam may be represented by a modified Bingham plastic model, with the addition of a liquid-rich slip layer caused by bubble migration away from a solid-surface. The model was applied to experimental results for cone and plate rheometer flow and pipe flow. It was found that the consistency and flow behaviour index are to a first approximation independent of expansion ratio and bubble size. The yield stress is dependent on bubble size distribution. The slip layer thickness depends on bubble size distribution and flow geometry, and is the most important parameter in pipe flow. There are changes in foam properties at an expansion ratio around 5 due to the change from gas emulsion to froth configuration.