Dissipation in quasi-two-dimensional flowing foams

The dissipation between two-dimensional (2D) monolayers of bubbles, the so-called quasi-2D foams, and a wall is investigated in two setups: a liquid pool system, where the foam is confined between a soap solution and a glass coverslip, and a Hele-Shaw cell, where the foam occupies the narrow gap between two plates. This experimental study reports dissipation measurements for mobile gas/liquid interfaces (free shear boundary condition) over a large range of parameters: in the liquid pool system, velocity and bubble area; in the Hele-Shaw cell, velocity and liquid fraction. The effect of the latter quantity is measured for the first time over more than three orders of magnitude. A full comparison between our results and other experimental studies is proposed and enables to rescale all measurements on a single master curve. It shows that for mobile gas/liquid interfaces, the existing models systematically underestimate the dissipation in flowing foams. This is quantified by a discrepancy factor xi, ratio of the experimental dissipation measurements to the theoretical predictions, which scales as xi=1.4(R(P)/root A)(-0.5) with R(P) the Plateau border radius and A the bubble area, showing that the discrepancy is higher for dry foams. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3142502]