Antifoam concentration, effect

Antifoam concentration, effect on flux, tangential flow filtration, 6l,63f... 

When starting a new water treatment program, both baseline and operational information regarding levels of steam and condensate contamination generally are required. It may take several weeks of sampling work to fine-tune the program and determine any limitations with regard to steam purity and quality. Thereafter, individual control parameters such as sodium limits or antifoam concentration may need to be selectively raised or lowered in the BW and the effects tested for in the steam. 

Figure 11. Effect of antifoam concentration on flux for an E. coli in a defined medium. Key clean water A, 0 ml/1 ...

The effect of the antifoam on the foam is best estimated if the total volume of liquid and gas is measured and the volume of air in the foam is used as a measure of either foamability or stability. The method is surprisingly reproducible even when comparing results obtained by different individuals. This is exemplified by a plot of F (= volume in air in the presence of antifoam/volume of air in the absence of antifoam) against logio(antifoam concentration) shown in Figure 2.1. This plot was prepared by three different individuals using a predispersed antifoam [4],... 

Effect of Antifoam Concentration on Volumes of Foam Generated by Air Entrainment in Aqueous Solutions... 

We first deduce the effect of antifoam concentration on generated foam volumes, which should result if we make the simple assumption that the relative effectiveness of different antifoams is independent of both antifoam concentration and foam volume for a given method of foam generation and surfactant solution. Comparison with the experiment is made. 

Equation 5.1 means that in any plot of foam volume or F against antifoam concentration, the gradient at a given value of F (= F or foam volume V, should be greater by a factor n for the most effective antifoam. This is illustrated schematically in Figure 5.1 from whieh it is easy to see that... 

This means that plots of F or foam volume against log(antifoam concentration) for antifoams of different effectiveness should all have the same gradient at the same value of F (= F°) or foam volume provided fl is constant. The plots should therefore be isomorphous. 

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]. 

The significance of Equation 5.26 can now be compared with the conclusions derived from the simple phenomenological approach described in Section 5.1. In the latter approach, the main assumption, we recall, was that the relative effectiveness of different antifoam dispersions is independent of antifoam concentration. This is expressed by Equation 5.1. It leads to the conclusion that plots of F against log(antifoam concentration) for different antifoams should be isomorphous. Experimental evidence that this is often observed is presented in Figures 5.2 through 5.5 (also see references [1,12,13]). 

Comparison of this theory with experiment is at present largely limited to the prediction of Equation 5.31, which is of course no advance on the simple phenomenological approach. However, in principle, some of the quantities in Equation 5.26 are either directly accessible by experiment or could be calculated. Clearly the effect of antifoam on bubble size distribution P(r ) could be measured but rarely is— no reliable data are apparently to be found in the published literature. Alternatively the effect of antifoam concentration on monodisperse foam volumes would be instructive. In this case. Equation 5.27 reduces to... 

The simple statistical theory presented here is clearly consistent with the phenomenological approach given in Section 5.1 in that Equations 5.3 and 5.15 can be derived from it That theory therefore affords some explanation for the success of the assumption, expressed in Equation 5.1, that the relative effectiveness of different antifoam dispersions can be adjusted to give the same foam volume, and therefore F, if their concentrations are adjusted in a fixed ratio, which is independent of foam volume and antifoam concentration. However, this theory uses a relatively simplistic statistical treatment that cannot effectively account for any fluctuations in the number of antifoam entities associated with films of a given size. In consequence, it is not... 

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