Foam factors

The vapor flooding velocity can now be calculated from Equation 8.3 assuming a foaming factor of 0.9 ... 

Williams, M. K., Holland, D. B., Melendez, O., Weiser, E. S., Brenner, J. R., and Nelson, G. L. Aromatic polyimide foams Factors that lead to high fire performance, Polym. Degrad. Stabil. 2005, 88, 20-27. 

If (V)(Ro) > 0.5, then replace 0.5 for (V)(Ro) in Equation 7-56. Table 7-4 gives recommended values of the foam factor and residence time. 

Using Table 7-4 to obtain both the foam factor (Foam fac) and the downcomer residence time, x, the downcomer area, is determined by... 

Recommended Values for Foam Factor and Residence Time... 

D = tower diameter, ft Foam fac. = foam factor (see Table 7-4)... 

Sieve trays with 10% hole area and 0.5 cm diameter holes will be used. Trays are available in standard diameters of 0.25 m increments (0.25,0.50, 0.75, 1, 1.25, 1.50,. .., m). Based on the top tray conditions, determine the required tray diameter rounded up to the nearest larger standard size. Assume a tray spacing of 0.5 m, a foaming factor of 0.80, and a fraction of flood of 0.80. The liquid density is given as 730 kg/m and the vapor density may be estimated based on the ideal gas equation. The liquid surface tension is 27 dynes/cm. 

The column has 3 m diameter sieve trays with 0.5 cm diameter holes and 10% hole area. The tray spacing is 45 cm. Assuming a foaming factor of 0.85, calculate the vapor flood velocity at the top tray. Check if the column diameter is acceptable. The fraction of flood velocity should be within a 60-85% range. 

Tray type Weir height Weir length Downcomer clearance Tray spacing Foaming factor Fraction of flood Surface tension Liquid viscosity... 

Sieve trays will be used with 60 cm spacing, 6 cm weir height, 0.6 cm hole diameter, 0.25 cm tray thickness, 5 cm downcomer clearance, and hole area 10% of the total tray area. The foaming factor is 0.80 and the froth density in the downcomer is 0.5. The target fraction of flood velocity is 0.70. 

Those factors that were previously mentioned that produce finer-textured foams also produce more stable foams. Factors such as surfactant type, concentration, increasing pressure, and higher inputs of mechanical energy generate more stable foams. For higher temperatures such as those that exist downhole, dynamic foam stability relies upon surfactant type and concentration rather than the addition of thickeners (polymer stabilizers). It is not known what rates are necessary to maintain dynamic stability in fractures, or whether those conditions typically exist. 

Design a sieve-tray column for the ethanol absorber of Example 4.4. For alcohol absorbers, Kister (1992) recommends a foaming factor Ff = 0.9. The liquid surface tension is estimated as a = 70 dyn/cm. Take do- 5 mm on an equilateral-triangular pitch 15 mm between hole centers, punched in stainless steel sheet metal 2 mm thick. Design for an 80% approach to the flood velocity. 

Values of Cp are used in (13-5) to compute the Souders and Brown capacity parameter C. Because the liquid flows contain a large percentage of absorber oil, a foaming factor, Fp of 0,75 is assumed. Also assume AJAa >0.1 so that Fha is 1.0. The value of Fst is determined from surface tension tr, which can be estimated for mixtures by various methods. For paraffin hydrocarbon mixtures, a suitable estimate in dynes per centimeter, based on densities, can be obtained from the equation... 

A short-cut correlation (354) for sizing self-venting lines is shown in Fig. 4.5. The author has had a lot of favorable experience with this correlation. With foaming systems, pipe diameter should be increased in proportion to the foaming factor (355). Caution with applying Fig. 

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