Dynamics of foam drainage

The drainage of liquid foams involves the interplay of gravity, surface tension, and viscous forces. Three experimentally accessible configurations are modeled analytically using a one-dimensional nonlinear partial differential equation called the foam drainage equation: free drainage where liquid drains from an initially uniform foam of fixed length, wetting of a dry foam, and pulsed drainage where a finite blob of liquid spreads in an otherwise dry foam. Similarity solutions are described in each case and compared with numerical solutions and available experimental data. The model is generalized to higher dimensions and used to discuss further examples of pulsed drainage.