Measurement and simulation of foam drainage in two dimensions using neutron Radiography

After coarsening and coalescence, foam drainage is one of the processes that dynamically influence foams. It is therefore of general interest to understand it in its principle behaviour. Liquid drainage is typically described by the unsteady, three-dimensional drainage equation [Verbist, 1996]. However, apart from optical observation in a Hele-Shaw cell [Hutzler, 2005], unsteady and multi-dimensional measurement of liquid fraction distribution is scarcely approached. Here, two-dimensional foam drainage experiments and simulations were carried out to validate the horizontal terms of foam drainage equation and to show its limitations. The two-dimensional liquid fraction distribution in steady, dynamic and periodic drainage experiments was measured with neutron radiography [Heitkam, 2018]. In particular, the damping character of the foam drainage was quantified as a function of different frequencies and amplitudes. This yields guidelines for forced-drainage experiments with peristaltic pumps.