Anti-bubbles

Some complex dispersions do not fit neatly into the earlier classical distinctions. For example, anti-bubbles are dispersed species of liquid-in-gas-in-liquid wherein a droplet of liquid is surrounded by a thin layer of gas that in turn is surrounded by bulk liquid. In an air-aqueous surfactant solution system, such a dispersion would be designated as water-in-air-in-water, or W/AAX/ , in fluid film terminology. Some examples are provided in Reference [83]. 

If the soap solution is poured rapidly into the bulk solution, it will sometimes penetrate deeper into the bulk solution and form an isolated bag of soap solution surrounded by a thin skin of air (Fig. 4.23). It is not always possible to obtain this result. However with experience bags of soap solution can be produced with up to 20 mm diameter. A bag is a spherical globule of soap solution surrounded by a thin shell of air existing in the bulk of the soap solution. This is the anti-bubble. , It is the inverse of a soap bubble. The soap film has been replaced by an air film, and the air contained inside and outside the soap bubble is replaced by soap solution. 

Once an anti-bubble has been formed it will move, under its own momentum, down into the bulk of the fluid. The buoyancy of the surrounding air will provide an upthrust which will cause it to slow down and eventually rise to the surface. On reaching the surface it will either bounce back into the fluid or come to rest nder the surface as a sphere or a hemisphere. 

Interference colours can be observed from the shell of air which is approximately 0.001 mm thick. The lifetime of these anti-bubbles may range from seconds to several minutes. They disintegrate suddenly, like the fluid droplets, and produce numerous air bubbles. 

The anti-bubbles are intrinsically unstable. The shell of air is contained between two spherical surfaces of fluid, one being convex and the other concave. The saturated vapour pressure of the inner surface is larger than the outer one. This will lead to evaporation from the inner sphere of fluid and condensation on the other concave surface of fluid. Also the film of air is intrinsically unstable against draining . 

In a 250 ml. distilling flask (1) place 122 g. (119 ml.) of p-phenylethyl alcohol and 40 g. of sodium hydroxide peUets (or 56 g. of potassium hydroxide). Heat is evolved. Warm gently until bubbles commence to form and the mixture separates into two sharply-defined layers. Distil slowly water, etc. passes over first accompamed by the gradual dis appearance of the upper phase. FinaUy the styrene passes over at 140 160° (mainly 150°) coUect this separately in a receiver containing about 0 1 g. of hydroquinone. Dry the distillate with a httle anhydrous calcium chloride or magnesium sulphate, and then distil under reduced pressure (2). C oUect the pure styrene at 42-43°/18 mm. The 3rield is 80 g. Add about 0-2 g. of hydroquinone (anti-oxidant) if it is desired to keep the phenylethylene. 

Anti-Jump Baffles Yes / No / Vendor Preference Recessed Seal Pans YeS / No / Vendor Preference Specify Equal Bubbling Areas / Flow Path Lengths per pass Design Load ... 

The entrainment of air in lubricating oil can be brought about by operating conditions (for example, churning) and by bad design such as a return pipe that is not submerged. The air bubbles naturally rise to the surface, and if they do not burst quickly, a blanket of foam will form on the oil surface. Further air escape in thus prevented and the oil becomes aerated. Oil in this condition can have an adverse affect on the system that, in extreme cases, could lead to machine failure. The function of an anti-foam additive is to assist in the burst of air bubbles when they reach the surface of the oil. 

When parts of an apparatus contain mercury, as in cut-ofiFs and McLeod gauges, it very often happens that air rushing in or out of the system will displace merciu in an undesirable manner. With cut-offs across a differential pressiue, bubbling of gas through mercury is unavoidable, and in tubing of internal diameter less than 3-4 mm bubbling will not occur but the gas will raise a column of mercury in front of it. It is therefore desirable to insert anti-splash traps wher-... 

Electrocarboxylahon of benzylic chlorides has been intensively investigated in the presence of a Ni(II) complex as a catalyst [274-277]. Eenoprofen (165), an anti-inflammatory agent, is electrosyn-thesized from (164) in a THE/HMPA-Bu4NBE4-(C/Ni) system in the presence of NiCl2 (dppp) as a mediator under bubbling... 

When a reaction mixture is heated, there is a tendency for it to boil violently as large bubbles of superheated vapour suddenly erupt from the mixture. This is prevented by the addition of the anti-bumping granules. A condenser is placed in the mouth of the flask and connected to a cold-water tap (water goes in at the bottom and out at the top). The flask is then heated and the vapours produced are condensed back into liquids when they reach the cool condenser. 

Calcium carbonate, either powdered limestone or precipitated chalk, is used as an anti-acid in dynamite where it serves as a satisfactory stabilizer. Urea is used in dynamite and in celluloid. It reacts with nitrous acid to produce nitrogen and carbon dioxide, and is unsuitable for use in smokeless powder because the gas bubbles destroy the homogeneity of the colloid and affect the rate of burning. The small gas bubbles however commend it for use in celluloid, for they produce an appearance of whiteness and counteract the yellowing of age. 

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