Foaming measurement

The stability of foams in constraining media, such as porous media, is much more complicated. Some combination of surface elasticity, surface viscosity and disjoining pressure is still needed, but the specific requirements for an effective foam in porous media remain elusive, partly because little relevant information is available and partly because what information there is appears to be somewhat conflicting. For example, both direct [304] and inverse [305] correlations have been found between surface elasticity and foam stability and performance in porous media. Overall, it is generally found that the effectiveness of foams in porous media is not reliably predicted based on bulk physical properties or on bulk foam measurements. Instead, it tends to be more useful to study the foaming properties in porous media at various laboratory scales micro-, meso-, and macro-scale. 

Gallart, M., Lopez-Tamames, E., Buxaderas, S. (1997). Foam measurements in wines compara-sion of parameters obtained by gas sparging method. J. Agric. Food Chem., 45, 4687 690. 

RobiUard, B., Delpuech, E., Viaux, L., Malvy, J., Vignes-Adler, M. and Duteurtre, B. (1993). Improvements of methods for sparkling wine foam measurements and effect of wine filtration on foam behavior. Am. J. Enol. Vitic., 44, 387-392. 

Figure 11. Evolution of carbon dioxide from reacting water-blown urethane foam measured by infrared absorbance. Key — — Formulation A ---------, Formula-...

Abstract. Infrared analysis of reacting foams has been used to determine the sequence of chemical reactions that occurs in the foaming process and to relate this sequence of reactions to the stages evident in the formation of foam measured by rate-of-rise techniques. A reaction sequence model has been developed in which at the earliest stage of foaming, out-of-phase carbamic acid and carbamic acid salts, formed by hydrolysis of isocyanate, are the main species present tending to stabilize the froth-like foam. These species are in turn converted into polyureas. In the latter stages of the reaction sequence, urethane formation becomes predominant as the foam develops substantial bulk modulus... 

Proteins in solution reduce the surface tension of the water and consequently aid in formation of food foams. Measure foam persistence, foaming power, and foam stiffness—whipped toppings, frozen desserts, chiffon mixes, angel food cakes, meringues... 

After a new catalyst charge is installed in an upstream unit, catalyst dust may be carried over into the column and induce foaming. Measures for preventing this should be considered. 

Fixed frequency and changed shear to the foam. Measured the deformation of the foam with oscillation frequency of 1 Hz, the different force applied to the foam, and deformation of the foam was observed. 

Figure 2.10. Schematic of the apparatus used in funnel-shaped testing. The foam volume, Uf, is calculated from the equations shown, where Af and Aq are the areas of the normal cross-sections at heights of hf and ho, respectively hf is the foam height and r is the radius of the base of the truncated cone. The steady-state volume is determined at a set gas flow and the slope of the foam volume versus gas flow curve gives the kinetic foam stability (lifetime of gas in the foam) measurement...

There are clearly a number of problems associated with most methods of foam measurement. 

More than half a century ago, Peper [195] considered the effect of sodium soaps and fatty acids on the foamability and foam stability of dilute solutions of anionic surfactant solutions. In this work, these soaps and fatty acids were present at a concentration of only 0.02 g dm (in the range of 0.6 X 10" -1.0 x 10 M depending on molecular weight). Peper does not make clear the state of these materials dispersed in the surfactant solution. However, the concentrations of surfactant appeared to exceed the CMC in most cases and it seems likely that both sodium soaps and fatty acids were solubilized. Foam measurements were made using hand shaking of measuring cylinders at 25°C. 

Garrett [1] has reported what is apparently the only observation of the effect of the concentration of a mixed antifoam dispersion on F (or foam volume). Results are shown in Figure 5.5 where F is plotted against log(antifoam concentration). Here dispersion C was prepared by mixing dispersions A and B in a fixed proportion. Dispersions A and B were each prepared using only one antifoam species. The two different antifoams are both mixtures of hydrophobic particles and hydrocarbon oils—a commercial calcium alkyl phosphate-liquid paraffin (dispersion A) and a hydrophobed silica-liquid paraffin (dispersion B). All the dispersions were made using a solution of a commercial sodium alkylbenzene sulfonate. Foam measurements were done using a static Ross-Miles apparatus [1]. 

F = volume of air in foam in presence of hexadecane/volume of air in foam in absence of hexadecane F (t = 300 s)/F (t = 0) is ratio of F at t = 300 stoFatf = 0asa measure of antifoam effects as the foam ages. If, for example, F (300 s)/F (t = 0) < 1, then the antifoam has continued to have effect during 300 s after foam generation ceased. Foam measurements made by hand shaking measuring cylinders. Antifoam concentration 1.0 kg m . 

Foam measurement methods are often empirically classified as static and dynamic methods. 

J is the polar moment of inertia of the circular cross-section, and 0 is the relative angular displacement of the ends of the specimen. If the material is not isotropic, however, the resulting quantity is not truly the modulus of rigidity, except when the axis of the cylinder lies in certain directions depending upon the anisotropic symmetry of the material. The plastic foams measured here were not isotropic, but it will be convenient to call the property measured by this method the modulus of rigidity for the moment, bearing in mind that it is an approximation. 

Figure 44 Apparent density and compressive strength of poiyurethane foams measured in parallel and perpendicular rise directions. Reproduced from Bogdal, D. Prociak, A. Pielichowski, J. In Application of Microwave Irradiation for Chemical Recycling of Polyurethanes, Proceedings of Global Symposium on Recycling, Waste Treatment and Clean Technology, REWAS, Madrid, 2004." ° ...

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