Methods for Defoaming

C. Zychal. Defoamer and antifoamer composition and method for defoaming aqueous fluid systems. Patent US 4631145,1986. 

There are many laboratory methods for testing the relative merits of one defoamer against another. It is a simple matter to measure foam height as a function of time to compare the performance of various foam surfactants and defoamers. Unfortunately, this simplicity has led to a wide variety of methods and conditions used with no standard procedure that would make the measurement of foaminess as characteristic of a solution as its surface tension or viscosity. It has been suggested that the time an average bubble remains entrapped ia the foam is such a quantity (49), but very few workers ia the defoamer iadustry have adopted this proposal. Ia practice, a wide variety of methods are used that geaerally fall iato oae of five maia categories ... 

Tsuge et al. [11] present a comparison of three methods for estimation of the defoaming ability i) by the decrease in height of a foam column, produced by pouring the solution (Ross-Miles method) after antifoam introduction the height is measured immediately after foam formation and after 5 min... 

As we describe in detail elsewhere in this book, effective antifoams are usually both oil-based and insoluble in the medium to be defoamed. In order to function, it is necessary that the oil exhibit the property of emerging into the air-liquid surface of that medium. In turn this requires that the film of foaming liquid separating the oil from the air be unstable. The stability of these so-called pseudoemulsion films [1] is therefore a key issue in determining antifoam effectiveness. We therefore review the methods for studying such films. 

In this section we shall present a simple method for estimating the submergence required to prevent incoming vapor from escaping out the bottom opening of a defoaming cyclone. From fluid statics, we know that the hydrostatic pressure at the bottom opening of the cyclone, at elevation z = 0 (see Fig. 14.4.1), must equal the hydrostatic pressure at this same elevation outside the cyclone. This leads directly to the relationship ... 

Turcotte and Lockwood [104] reported the development of a heavy-duty automobile antifreeze composition that used Pluronic L-61 at 0.05% by weight as a defoamer. Schubert et al. [105] described a method for cleaning that used automobile antifreeze via an ion exchange/carbon bed and then reintroducing necessary performance enhancing additives. The authors reported using Pluronic L-61 as the primary antifoam agent in the reconstituted material. 

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