Measurement of Foam

1 Bartsch Method FIand Shaking Measuring Cyeinders 

Shaking a glass vessel, such as a measuring cylinder, vigorously for a fixed time interval (typically for 10-15 s) represents an easy approach to assessing the effectiveness of an antifoam in aqueous surfactant solntion. The method has occasionally 

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. 

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Foaming characteristics of lubricating oils NFT 60-129 ISO/DIS 6247 ASTM D 892 Air sparging and measurement of foam after standing... 

Barring direct measurement of foam texture, we adopt the following reasoning. Because of the generation of foam bubbles by the snap-off and division mechanisms (4), bubble sizes are expected to be approximately that of pore bodies. Thus, the linear bubble density should scale roughly as n 6/Dwhere... 

Some important aspects of foam are not included in this list. We mentioned void volume earlier. This parameter is related to density by a comparison of bulk density to absolute density. We will discuss each of these measures of foam quality and relate their applicability to the theme of this book. Later in the chapter we will show how formulation and processing techniques are used to adjust and control the most important parameters. 

Food foams are usually made by bubbling, whipping, or shaking a protein-containing solution. Several measures of foaming capacity of proteins and other stabilizing agents exist, such as overrun, which quantifies the amount of foam produced, defined as ... 

The common understanding of foam stability usually refers to the ability of a foam to maintain its main parameters constant with time, i.e. bubble size, liquid content (expansion ratio) and total foam volume. Foam lifetime is most often used as the simplest measure of foam stability. 

The direct measurement of the various important parameters of foam films (thickness, capillary pressure, contact angles, etc.) makes it possible to derive information about the thermodynamic and kinetic properties of films (disjoining pressure isotherms, potential of the diffuse electric layer, molecular characteristics of foam bilayer, such as binding energy of molecules, linear tension, etc.). Along with it certain techniques employed to reveal foam film structure, being of particular importance for black foam films, are also considered here. These are FT-IR Spectroscopy, Fluorescence Recovery after Photobleaching (FRAP), X-ray reflectivity, measurement of the lateral electrical conductivity, measurement of foam film permeability, etc. 

Optical measurements of foam films are very complicate. In order to have a clear and precise interpretation of the results, especially for the thinnest black films, it is necessary to make models. The simplest and the most widely used one is the three-layer model (see Section 2.1.3). 

Optical techniques for measurement of foam film thickness involve different models and plotting the optical parameters it is possible to find the real film structure. In this sense it is interesting to compare h(Cei) dependence of lyso PC films in the presence of CaCl2 depicted by two independent optical techniques microinteferometric (Fig. 3.50) and FT-IR spectroscopy [193,292]. In this case the thickness of the aqueous core d2 is determined from... 

The parameter tm is introduced as a measure of foam stability, i.e. the lifetime of foam layer at a distance about 2 cm from the a-source (this distance corresponds to one half of the free path of the a-particles). Table 7.2 summarised the results obtained for foams from various surfactants. 

The method for investigating foams at high pressure drop in Plateau borders permits the estimation of foam stability under strictly defined conditions (see Section 7.2). This method enables measurement of foam lifetime tp at a certain constant pressure as well as at reaching the critical state of the film. 

Foams from Triton-X-100 solutions (10 3 mol dm"3), containing NaCl (0.4 mol dm"3) were studied. The foam volume was 40 cm3. Foam expansion ratio was regulated by changing either the time for foam drying or the pressure Ap in the solution, contacting the porous plates. Conductometric measurements of foam expansion ratio were performed for comparison. 

Figure 5. Measurements of foaming ability and foam stability for samples of raw foam, and humic substances from stream, foam, and foam extract samples from Como Creek and Suwannee River. Final foam heights were recorded after 5 minutes.

Several other techniques have been appHed for the measurement of foam films, including ellipsometry, Fourier transform-infrared (FT-IR) spectroscopy. X-ray reflection, and the measurement of gas permeabihty through the film. These techniques are described in detail in the text by Exerowa and Kruglyakov [4] to which the reader is referred. 

Figure 10. Foam half-life measurements of foam stability and foam height measurements of foaminess versus dilatational elasticity for aqueous foams stabilized by a-olefin sulfonates. (Reproduced from reference 22 Copyright 1986 American Chemical Society.)...

Of course, the final test by which to assess the requirement that the surfactant should be capable of maintaining lamellae for mobility control in C02 floods is the measurement of foam mobility in cores. Because such tests are time-consuming and expensive, the foam durability test has been used as a useful screening tool for more rapid appraisal of surfactants at reservoir conditions. 

The effect of gas velocity at a constant liquid velocity on the relative permeability to gas (fcfg) is shown in Figure 5, for a sand pack of 2-darcy absolute permeability containing residual oil after steam-flooding (15 pore volume) at 180 °C (28). The fcrg is a measure of foam flow resistance the... 

Foam Effectiveness in Porous Media. No generally accepted correlations exist between foam characteristics measured outside the porous medium and foam effectiveness as a gas mobility-reducing agent in porous media. The performance of the nine surfactants that passed the solubility criteria was therefore evaluated in porous media under typical reservoir conditions. The results of such an evaluation can be expressed in several ways. One of the simplest measures of foam effectiveness, and arguably the most straightforward one, is the mobility-reduction factor (MRF). The MRF is defined as the ratio of pressure gradients across a... 

As a measure of foam stability, the rate of foam formation Wp was proposed when a foam is produced [19]. This parameter can be determined experimentally on the basis of consideration of the balance of air volumes used to obtain the foam. 

For mousses, measurement of foam properties including foam volume, foam quality, and foam stabihty is critical to the performance of this type of product. Although such tests have not been described for mousse evaluation, per se, minor modihcation to shave cream foam tests should provide satisfactory procedures. 

Crompton gives several important suggestions regarding corrective measures of foam defects, as follows ... 

Foam Size Analysis To determine the biabble size, a plexiglass cell (2 X 2") was constructed for the measurements of foam size. The surfactant solution (10 ml) was placed into the cell, and foams were generated by shaking the cell for a constant time, (e.g. 2 minutes). An average bubble size was determined from the size frequency analysis. 

The experimental set up is also equipped with a high resolution CCD camera. Pictures of the batch/glass melt in the vitreous silica crucible are taken at regular intervals. These images can be used for, for example, detailed observation of the reactions taking place, onset of melting phase formation, measurement of foam amount, and determination of the fining onset... 

Figure 12. Measurement of foam layer thickness from high temperature images...

Gas bubbles created by vacuum - measurement of foam volume... 

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