Foam generation dispersion

Foam generated in porous media consists of a gas (or a liquid) dispersed in a second interconnected wetting liquid phase, usually an aqueous surfactant solution (1). Figure 1 shows a micrograph of foam flowing in a two-dimensional etched-glass porous medium micromodel (replicated from a Kuparuk sandstone, Prudhoe Bay, Alaska (2)). Observe that the dispersion microstructure is not that of bulk foam. Rather discontinuous... 

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. 

Stream type foam generators (air-foam tubes) and foam generators in which the dispersing device is gauze have wide application, especially for fire-fighting and dust-catching foams [37-38]. 

A great advantage of mixing foam generators is the possibility to regulate both foam expansion ratio and dispersity, though within a narrow range of alterations. For example, at constant ratio of gas and liquid volumes the dispersity of foam increases when the consumption of liquid and gas rises [45]. 

The properties of a low expansion ratio foam are controlled mainly by changing the rate of the kinetic processes running in it. To decelerate the hydrodynamic processes in order to preserve its structure for a longer time (for instance, in the formation of polymer or frozen foams), the following measures can be recommended i) to use a foam generation mode that allows producing a foam of a uniform expansion ratio such are the stream type generators and some mechanical devices that mix the solutions ii) to produce a foam of maximum dispersity... 

The accumulation ratio //min increases with the decrease in bubble size only if n = const (Eq. (10.11)). If the expansion ratio changes simultaneously with dispersity (as is often the case under the conditions of gravitational drainage since the decrease in foam bubble size results in a decrease in the rate of drainage and in the formation of a low expansion ratio foam at the outlet of the foam generator), then a decrease in bubble size leads to a decrease in mm rather than to its increase [23,67]. 

Food foams are dispersions of gas bubbles in a continuous liquid or semisolid phase. Foaming is responsible for the desirable rheological properties of many foods, e.g., the texture of bread, cakes, whipped cream, ice cream, and beer froth. Thus foam stability may be an important food quality criterion. However, foams are often a nuisance for the food processor, e.g., in the production of potato starch or sugar and in the generation of yeast. Residues of antifoaming aids in molasses may drastically reduce the yield in citric acid fermentation. 

Solubilizer, foaming agent, dispersant, emulsifier and surface tension reducer. High electrolyte tolerance. Generates small particle size vinyl acetate and acrylic polymer emulsions. 

For generations, attempts have been made to heat and cool foams, emulsions, dispersions, and heterogeneous colloidal systems, and to learn about the stability of the systems through their thermal behavior. Differential scanning calorimetry (DSC) and differential thermo gravimetry (DTG) are classical instruments that... 

Antifoam may be added to the relevant solution in the vessel directly by weighing out the relevant quantity onto a microscope sUde coverslip. This method has the disadvantage that dispersal of the antifoam and foam generation occur simultaneously. Preferably, therefore, the antifoam should be predispersed using ultrasonics or a suitable emulsifier/mixer (such as an Ultraturrax ) and the dispersal characterized (by light scattering or optical microscopy). The effect of antifoam on the foam as a function of concentration can then be readily determined by dilution of the dispersion with the surfactant solution. 

Antifoams are often conveniently dispersed into foaming systems in the form of emulsion drops or individual particles. Here we assume that the concentration, state of dispersion and the effectiveness of each antifoam entity in such antifoam dispersions remain constant during foam generation. These assumptions therefore... 

If, in the case of a given method of foam generation and surfactant solution, the relative effectiveness of an antifoam dispersion can be adjusted by simply increasing the relative concentration, then we can write... 

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