DYNAMICS OF FOAM FILMS IN CONSTRICTED PORES

Hydrodynamics of foam films in a porous medium depend strongly on the pore geometry, foam quality, foam flow rate, surfactant formulation, r heological properties of the film, and the capillary pressure in the m edium. These dynamics were studied numerically by simulating the behav ior of a foam film as it traverses a periodically constricted sinusoid al pore. Different regions of film behavior exist depending on ifs rhe ological properties. For a film with rigid (immobile) surfaces, the en trainment effect leads to a thickening film consistent with related ph enomena such as Bretherton's (1961) analysis of a bubble moving in a c apillary tube. A film with mobile surfaces, however, stretches and thi ns while remaining uniform in thickness and may become unstable under certain conditions. The dependence of limiting capillary pressure on t he foam flow rate and rheological properties is explained quantitative ly.