Foam decay

Similar results have been obtained for other foaming compositions [21,44]. These data indicate that Tr coefficients depend slightly on foam expansion ratio but the decrease is almost twice at level H = 2 cm, which means that the foam decay more intensively at its higher... 

However, the kinetic dependence of foam column decay proposed by Schwarz appears to be better grounded [8]. No attempts to relate the constants characterising the rate of foam column destruction with both physicochemical characteristics of the foaming solution and foam structure have been reported. The stepwise kinetics of decay of the foam column is typical for aqueous as well as non-aqueous foams. Manegold [32] points out that coarse foams decay in larger steps than finely disperse foams. 

In a centrifugal field, where visual observations of the foam layer destruction are difficult, the highest capillary pressure at which the foam decays rapidly (for about 1 to 3 min) is accepted as a critical pressure. 

When the foam decays in gravitational field the capillary pressure in its upper parts reduces due to the diminish of the foam column height. Hence, the time of decay of the local layers would be different while to total lifetime of the whole foam column would be an integral characteristic which accounts for the effect of local pressure and the total height of the foam column Ho-... 

For a 10 cm foam column, = 628 min. In order to compare the stability of foams decaying in gravitational field at a capillary pressure corresponding to the particular layer... 

Thus, it might be assumed that stabilisation of foam films will depend also on the action of other positive components of disjoining pressure. For example, equilibrium films are obtained from concentrated butyric acid solutions and, therefore, in this concentration range the foam lifetime also increases. On the basis of these concepts it should be expected that a foam consisting of films with equilibrium thicknesses at a constant capillary pressure pa = n, should be infinitely stable. In fact, a real foam decays both in bulk and as a disperse system, due to gas diffusion transfer and certain disturbances (shift of films and borders on structural rearrangement as a result of the collective effects , etc.)... 

The presence of salts (10% NaCl and 1% CaCh) and petroleum strongly accelerate foam decay, leading to decrease in gas permeability [161]. The increase in permeability due to crude oil depends significantly on the type of the foaming solution. For a more stable foam the decrease in permeability is much less and the foam action pertains for over a month without continuos injection of the agent [161]. 

FOAMING. The foaming of Quatrlsoft IN 200 was studied by the conventional cylinder shake test. While the Immediate foam height of Quatrlsoft IM 200 was much higher than that of Polymer JR (30 ml vs. 10 ml), the foam decay results of Figure 5, show that the foam stability of the former polymer Is also much greater. 

Figure 1 Typical evolution of foam volume with time obtained by a sparging method. Q = 5l/h. Insert shows thee definition of foam decay characteristic times...

Loss of Gas Blockage. In steady-state flow of foam, the major mechanism of foam decay is dynamic capillary suction coalescence (41, 51). This process may occur in earlier stages of an experiment with gasblocking foam but is expected to be less frequent later in the experiment. 

Then, Vfi is the velocity of collapse in the process of foam formation, and Vi/t is the rate of foaming. Thus, V3/t is the rate of foam decay in the process of its formation Wp°. Hence we can write... 

Thin films are highly susceptible to outer influences which, under the conditions of a dynamic structure of high-expansion foams, leads to an increase in the rate of foam decay as the electrolyte concentration increases. This is obviously due to the determining contribution of the foam rupture to the stability of the foam structure at its formation which is confirmed by a typical crack observed when foam is generated from solutions having a high electrolyte content. This phenomenon is not observed in absence of electrolyte. 

New batch compositions can be studied to see the effects on foaming, melting-in fining behaviour and to optimize a batch for fining. The use of alternative raw materials can be explored, as can the effect of furnace atmosphere on fining onset (temperature) or foaming. The equipment is well-suited to determine foam decay rates, or the fining onset temperature (for... 

Surface-Active Materials. The active defoamer components are necessarily surface active materials, but this ancillary category covers the surfactants that are often incorporated in the formulation for other effects such as emulsification or to enhance dispersion. Emulsifiers are essential in the common oil-in-water emulsion systems, but they are also required where mixtures of active liquid components are used. For example, specialized oil-in-oil emulsifiers are needed in defoamers based on silicone/polyether mixtures, oil-in-water emulsifiers are incorporated in some defoamers even when the final product contains no water. This is to promote emulsification (self-emulsifiable) or dispersion into aqueous foaming systems. These additives increase the speed of foam decay by promoting rapid dispersion of the defoamer throughout the foaming media. Examples of emulsifying agents used in defoamer compositions are fatty acid esters and metallic soaps of fatty acids fatty alcohols and sulfonates, sulfates, and sulfosuccinates sorbi-tan esters ethoxylated products such as ethoxylated octyl or nonylphenols and silicone-polyether copolymers. 

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