Foam numbers

A relative drainage rate test in which a foam is formed in a vessel and thereafter the remaining foam volume is determined as a function of time. The foam number is the volume of bulk liquid that has separated after a specified interval, expressed as a percentage of the original volume of liquid foamed. 

The techniques employed in foam drainage investigations involve the determination of liquid quantity that drains from the foam per unit time. Different foam numbers were introduced as indirect drainage characteristics of low expansion ratio foams produced by the... 

There are various types of vessels and graduated tubes used in the precise measurement of the liquid quantity draining from a foam [1,14,19-21]. A procedure is proposed for measuring the time interval from the moment of foam formation to the moment at which the liquid begins to drain. The foam is placed in a cylinder, and similarly in the determination of StiepeTs foam numbers [14,19], is turned upside down, and the falling of the first liquid drop is recorded [6,22]. 

As measured by the modified JIS desiccator procedure, pressed wood products had the highest release rate coefficients expressed as a function of surface area (Table IIA) of the various sample types tested. Release rate coefficients from urea formaldehyde foam products were comparable to those of pressed wood products (Table IIB). Products labelled substrate (sub 1, sub 2, and sub 6) were experimental foams. The drywall that had been placed next to the foams (Number 1, 2, or 3) for more than 1 week in a configuration similar to that in a building released a moderate amount of formaldehyde. 

In foams with high foam numbers the surface in Gibbs- Plateau borders is close to cylindrical, i.e. has a constant triangular-shaped cross-section with concave sides. The pressure in such cross-section is lowered in comparison with the pressure in foam cells by the amount of o/rcurv, where rcurv is the curvature radius of the border surface (i.e., of the side of triangle). 

In foams with foam numbers between 100 and 1000 (depending on the degree of dispersion in the system and film thickness) most of the dispersion medium is present in the borders and only little portion of it stays in the films. Liquid content in junction nodes is the highest in films with low foam numbers (close to 3). 

Fig. VIII-9. Change in the foam number, K, as a function of time for foams with high (curve 1) and low (curve 2) foam numbers...

Fig. 8.7 Weight loss data for 2 mm thin slices cut from interior layers of a (25 mm) HlOO foam number indicate slice location away from exposed surface). The weight loss from the outer layer...

The foam number, F, is often used for a crude comparison of foams and is defined as ... 

Example 13.1. Calculation of gas volume fraction from foam number. 

Bubbles in freshly poured beer are typically polyhedral. Using a laboratory test, the foam number of a beer foam has been measured to a value of 4. 

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