Mechanisms for the onset of convective instability in foams

We introduce new mechanisms for the onset of convective motion in loaded 3D foams. This is done by balancing gravity and capillarity along a liquid-filled channel for a microstructural model of foam drainage; the weight of this non-uniform-area channel is then used to predict the onset of instability. The predictions of these models are not very different from the gravitational model, although they do allow for the concept of localized deformation and shearing of a foam. Comparison is made to existing experimental data by incorporating the dependence of yield stress on liquid fraction, which is found to have a large effect on onset.