The Importance of Foams

The presence of foam in an industrial product or process may or may not be desirable. Foams have wide technical importance, as such, in the fields of fire fighting, polymeric foamed insulation, foam rubbers, and foamed structural materials such as concrete, whipped cream, shaving cream, and many areas of the baking industry. They also have certain esthetic utility in many detergent 

FIGURE 12.1. There are two general classes of foams, the dilute foams (a) in which the gas bubbles are well separated and spherical, and the concentrated foams (b) in which the bubbles are closely packed so that their shape becomes distorted from the spherical. 

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The difference found in the behaviour of steady-state foams from NaDoS solutions in the presence of various electrolyte concentration reflects the importance of foam films, which can be formed also in such systems. The existence of different types of foam films in the steady-state foams is proved by their destruction by a-particle irradiation [121], Fig. 7.23 shows the dependence of the foam column height on the electrolyte concentration. It is seen that at NaCl concentration higher than 0.35 mol dm 3, H does not change. This concentration is very close to the electrolyte concentration at which there occurs a transition from one foam film type to another. 

In the present paper, pore level descriptions of bubble and bubble train displacement in simple constricted geometries are used in developing mobility expressions for foam flow in porous media. Such expressions provide a basis for understanding many of the previous core flood observations and for evaluating the importance of foam texture and interfacial mobility. Inclusion of the effects of pore constrictions represents an extension of the earlier efforts of Hirasaki and Lawson (1). 

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