From "discrete" to "continuum" flow in foamsS. Rodts1, J. C. Baudez2 and P. Coussot1
1 LMSGC (UMR113 LCPC-ENPC-CNRS), Institut Navier Champs sur Marne, France
2 Cemagref - Domaine des Palaquins, Montoldre, France
received 22 July 2004; accepted in final form 3 December 2004
published online 14 January 2005
From both NMR and conventional rheometrical data we show that a foam cannot flow steadily below a critical, apparent shear rate and a critical shear stress. At low velocities the shear localizes in a layer of thickness decreasing with the apparent shear rate. When this thickness becomes smaller than a critical value (about 25 bubble diameters) the continuum assumption is no longer valid and the apparent behavior in this "discrete" regime differs from the rheological behavior of the foam in the "continuum" regime (for a sheared thickness larger than ).
83.80.Iz - Emulsions and foams.
83.10.Gr - Constitutive relations.
83.60.La - Viscoplasticity; yield stress.
© EDP Sciences 2005