Gas emulsion

If, by one of the above procedures, a few or even many bubbles have been introduced into a liquid, there is still no foam. In a foam, films between the bubbles are thin otherwise, the system is a gas emulsion. How, then, can a true foam be achieved If it is assumed that, because of some kind of stirring, two bubbles move to meet each other and the liquid layer between them gets thinner and thinner and if this process continues for a sufficient time, the two bubbles will touch and, eventually, coalesce. Many such encounters would destroy the foam. It is clear, therefore, that bubbles should be free to approach each other closely, but should be unable to cross the last short fraction of the initial distance. 

A dispersion of gas bubbles in a liquid, in which at least one dimension falls within the colloidal size range. Thus a foam typically contains either very small bubble sizes or, more commonly, quite large gas bubbles separated by thin liquid films. The thin liquid films are called lamellae (or laminae ). Sometimes distinctions are drawn as follows. Concentrated foams, in which liquid films are thinner than the bubble sizes and the gas bubbles are polyhedral, are termed polyederschaum . Low-concentration foams, in which the liquid films have thicknesses on the same scale or larger than the bubble sizes and the bubbles are approximately spherical, are termed gas emulsions , gas dispersions , or kugelschaum . See also Evanescent Foam, Froth, Aerated Emulsion. 

Foam is a disperse system, consisting of gas bubWes, separated by liquid layers. Dispersion of gas in liquid in which the gas cortect is low and the thickness of liquid layers is commensurable to gas bubble size is called gas emulsion or spherical foam ( kugelsctiaiim by Manegold l l ). The shape of bubbles in die gas emulsion is spherical (if their size is not very big) and there is no contact between them. 

A simple and largely applied method for foam formation is dispersion of gas through porous plates (filters) placed at the lower parts of foam generation apparatus [5-10], This method is employed in flotation, in gas adsorption and dust collection in set-up with turbulent gas emulsion, and in the equipment for foam separation. The dispersity of a foam thus obtained depends on filter pore size or capillary diameter, hydrophility of the material used in the dispersion device construction, physicochemical properties of the foaming solution (surface tension, viscosity, surfactant concentration, etc.) and conditions of the dispersion process. 

At the onset of formation by barbotage methods the foam represents a gas emulsion. The rate of its transformation into a polyhedral foam depends on the velocity of bubble rise and the consequent drainage of the excess" liquid from the foam thus formed. Bubble size,... 

Dispersity of gas emulsions and polyhedral foams is a very important parameter which determines many of their properties and processes occurring in them (diffusion transfer, drainage, etc.) and, therefore, their technological characteristics and areas of application. The kinetics of changes in dispersity indicates the rate of foam inner destruction resulting from coalescence and diffusion transfer. In real foams bubble size varies in a wide range (from micrometers to centimetres). Only by means of special methods it is possible to obtain foam in which bubble size varies in a narrow interval, i.e. foam that can be regarded as monodisperse. 

Bubbles of large diameter (from 1 to 7 cm) in a gas emulsion obtained in the absence of surfactant are analysed. 

As mentioned above, at low gas volume fraction the shape of bubbles in a gas emulsion is close to spherical and the excess pressure in them (compared with pressure in the bulk liquid) equals 2a/R. 

Theoretical and semi-empirical equations were derived for gas emulsions (as well as for suspensions of non-conducting spherical particles and O/W emulsion), specifying Eq. (8.33) . A relation for coefficient B can be derived from Maxwell-Wagner equation [45,46]... 

Emulsions are dispersions of one fluid into another. Both oil-in-water and water-in-oil emulsions are encountered. Foams are similar to emulsions, but the dispersed phase is a gas. Emulsions are everywhere some examples of products that are based on emulsions are salad dressings, mayonnaise, egg yolk, milk, margarine, cream, ice cream, waterborne paints and bitumen. Emulsions are generally not stable, so they need to be stabilized against coalescence. One can use surfactants for that, or polymers, such as proteins and polysaccharides, or particles. 

Gas Emulsion A term used to describe crude oil that contains a small volume fraction of dispersed gas. 

A foam structure can always be formed in a liquid if bubbles of gas are injected faster than the liquid between bubbles can drain away. Even though the bubbles coalesce as soon as the liquid between them has drained away, a temporary dispersion is formed. An example would be the foam formed when bubbles are vigorously blown into a viscous oil. Such a foam, comprising spherical, well-separated bubbles, is referred to as a wet foam, or kugelschaum. Wet foams in which the liquid lamellae have thicknesses on the same scale as the bubble sizes are sometimes referred to as gas emulsions . Here, the distinction of whether this is a foam or not relates to stability. But it is complicated by the fact that, as for other types of colloidal dispersions, no foams are thermodynamically stable. Eventually they all collapse. 

Gas Emulsion Wet foams in which the liquid lamellae have thicknesses on the same scale or larger than the bubble sizes. Typically in these cases, the gas bubbles have a spherical rather than polyhedral shape. Other synonyms include Gas Dispersion and Kugelschaum. In petroleum... 

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