The Apparent Viscosity of Foams in Homogeneous Bead Packs

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Abstract
Summary: The mobilities of aqueous foams of known texture have been measured in homogeneous bead packs. To correlate the data, a theory developed recently to describe the apparent viscosity of foams in smooth capillaries is extended to account for (1) the capillary pressure imposed by the porous medium and (2) constricted flow paths. In porous media, apparent gas viscosity depends strongly on foam-bubble size; for large bubble sizes, it is proportional to the third power of the ratio of the hydraulic radius of the pack to the bubble radius. Foams of uniform texture are pseudoplastic. At low shear rates, the viscosity varies inversely with a capillary number; at higher rates, it depends on the capillary number to the - ⅓ power when the bubble size is large compared with the pore size and on the - ⅔ power of capillary number when the bubble size is smaller.