Bubbles coagulation

Fig. 5 Boiling in a narrow vertical tube. (A) Boiling suppressed by head, natural convection is shown (B) bubble formation (C) slug formation due to bubble coagulation (D) fully developed slug flow (E) breakdown of slugs at high vapor rates (F) annular-flow-climbing film.

If the polydispersity of bubbles generated in air-dissolved flotation or electroflotation is high, there is no need for additional introduction of centimicron bubbles. Optimal flow of two-stage flotation corresponds to the maximum attainable degree of monodispersity of bubbles. In this case the ratio between volume fractions of micro- and macrobubbles and collision efficiencies of the processes of particle capture by small bubbles and bubble coagulation must be such that the particle capture process outweighs the process of coalescence. 

In dipping generally, but particularly with the anode process, it is desirable to use tanks that circulate the coagulant and latex compound, particularly the latter. Use of circulation keeps the Hquid surface clean and free from lumps, scum, or bubbles. Mechanical circulation can cause mbber particle instabihty, however, and eventually coagulate the compound. Therefore, tanks should be designed to minimize friction or shear action, and the compound stabilized to maintain mechanical stabiUty. 

Equation (17) indicates that the entire distribution may be determined if one parameter, av, is known as a function of the physical properties of the system and the operating variables. It is constant for a particular system under constant operating conditions. This equation has been checked in a batch system of hydrosols coagulating in Brownian motion, where a changes with time due to coalescence and breakup of particles, and in a liquid-liquid dispersion, in which av is not a function of time (B4, G5). The agreement in both cases is good. The deviation in Fig. 2 probably results from the distortion of the bubbles from spherical shape and a departure from random collisions, coalescence, and breakup of bubbles. 

DAF is usually designed by pumping compressed air bubbles to remove fine SS and FOG. The wastewater is first stored in an air-pressured closed tank and then enters the flotation tank through pressure-reduction valves. Due to a sudden reduction in pressure, air bubbles form and rise to the surface in the tank. SS and FOG adhere to the fine air bubbles and are carried upward. Both dosages of coagulant and pH are important in the removal of BOD5, COD, FOG, and SS. Other important... 

In the empty tube, bubble and droplet sizes are clearly smaller and hence specific surface areas at the G/L- and L/L-interphase are higher than with the static mixers. Obviously, contact of the dispersed phases with the mixer plates supports the coagulation of bubbles and droplets. However, the overall reaction... 

II Figure 1). Adsorption continually occurs around the bubbles to replace protein in areas of the interface where coagulation or stretching of the film is occurring. The actual bubble size in the foam depends upon the rate of protein adsorption as well as upon the ease of film rupture. The protein films on adjacent bubbles come in contact and trap the liquid, preventing it from flowing freely. This restriction is governed by the viscosity of the colloidal solution. The polypeptides of denatured proteins situate to positions where their hydrophobic side chains are directed outward toward each other. Because liquid... 

A stream of carbon dioxide is bubbled through a mixture of 133 ml. (1.64 moles) of ethylenediamine monohydrate and 133 ml. of water cooled in ice. The stream of carbon dioxide is maintained during the entire preparation. A solution of 195 g. (0.82 mole) of cobalt(II) chloride hexahydrate in 175 ml. of water at room temperature is added to the cold solution, which is continually stirred. The addition of the cobalt(II) salt causes a violent evolution of carbon dioxide gas, and the solution becomes red-violet. (Sometimes the mixture coagulates and becomes gel-like.) The cooling and the stirring are continued, and the mixture is oxidized by dropwise addition of 200 ml. of 30%... 

Figure 12.2 Illustration ofthe elementary process steps in flotation de-inking. From left to right, detachment ofinkfrom fibres, coagulation ofink particles, attachment ofinkto gas bubbles, which are then floated.

In the absence of 02, Fe is oxidized to Fe2+ and Fe(OH)2 is formed. However, Fe(OH)3 precipitates more easily than Fe(OH)2 and, thus, the injection of 02 facilitates pollutant removal. The injection of gas also helps in the flotation process. Vik et al. [162] have described a process in which H2 is produced at the cathode and Al is oxidized to Al(III) ions at the anode. The OH generation from H2 evolution produces precipitation of the metal hydroxides and also contributes to the coagulation-flocculation process. In addition, the hydrogen gas bubbles result in the flotation of the sludge formed. The principles of such a process are depicted in Fig. 24. 

Il in and Sedashova [179] have described an electroflotation method and a small-sized plant to remove oil products from effluents based on adhesion of pollutant particles to finely divided bubbles of H2 and 02 produced during the electrolysis of water. From an initial petroleum product concentration of 1000 mg L-1, a residual concentration of 1 10 mg L-1 was found following electroflotation. This concentration could be further reduced to about 0.01 mg L-1 by the addition of inorganic coagulants. 

---