Gas bubble size

Because the reaction takes place in the Hquid, the amount of Hquid held in the contacting vessel is important, as are the Hquid physical properties such as viscosity, density, and surface tension. These properties affect gas bubble size and therefore phase boundary area and diffusion properties for rate considerations. Chemically, the oxidation rate is also dependent on the concentration of the anthrahydroquinone, the actual oxygen concentration in the Hquid, and the system temperature (64). The oxidation reaction is also exothermic, releasing the remaining 45% of the heat of formation from the elements. Temperature can be controUed by the various options described under hydrogenation. Added heat release can result from decomposition of hydrogen peroxide or direct reaction of H2O2 and hydroquinone (HQ) at a catalytic site (eq. 19). 

Fig. 12. Effect of gas bubble size on performance of fluidised beds.

Strickland concluded from these studies that oil removal is improved by increasing the ail drop size and gas concentration, and by decreasing the gas bubble size. Although Strickland did not rank the variables studied, he did report that frother concentration had a significant influence on oil removal... 

Figure 5.3-8. Details of the chum-turbulent flow regime of BSCR according to Inga [1], (db)0-gas bubble size at atmospheric conditions in the absence of solid particles, (d, )ps- bubble size at the operating pressure and catalyst concentration. Column height = 2.8 m, internal diameter = 0.316 m. P < 8 bars. Organic media, catalyst diameter < 100 pm.

Foam is a disperse system, consisting of gas bubWes, separated by liquid layers. Dispersion of gas in liquid in which the gas cortect is low and the thickness of liquid layers is commensurable to gas bubble size is called gas emulsion or spherical foam ( kugelsctiaiim by Manegold l l ). The shape of bubbles in die gas emulsion is spherical (if their size is not very big) and there is no contact between them. 

The pressure Pout, which is produced at the outlet, enables the current distribution over the WP surface to be changed. This is associated, to a large degree, with the fact that the gas bubble size decreases with an increase in Pout- The void fraction and its effect on the current distribution decrease. At a certain ratio between the inlet pressure and Pout, the nonuniformity of the current distribution may be significantly reduced. 

In this chapter, we discuss much of the work accomplished since Fried, but without attempting a complete review. Useful synopses are available in the articles and reports of Hirasaki (2, 3), Marsden (4), Heller and Kuntamukkula (5), Baghidikian and Handy (6), and Rossen (7). Our goals are to present a unified perspective of foam flow in porous media to delineate important pore-level foam generation, coalescence, and transport mechanisms and to propose a readily applicable one-dimensional mechanistic model for transient foam displacement based upon gas-bubble size evolution [i.e., bubble or lamella population-balance (8, 9)]. Because foam microstructure or texture (i.e., the size of individual foam bubbles) has important effects on flow phenomena in porous media, it is mandatory that foam texture be accounted for in understanding foam transport. 

The range of gas bubble sizes observed in the froth samples also corresponds closely with the estimates made earlier based on Houlihan s measured rising droplet sizes, where froth gas bubble sizes of about 216 140 pm were predicted. Table III shows that the mean bubble sizes fell in the range 200—500 pm. Here again, although the mean bubble sizes were consistently in that range, some bubbles as large as 1000 pm and as small as <100 pm were observed. 

Boyd JWR and Varley J (1998) Sound measurement as a means of gas bubble sizing in aerated agitated tanks. AIChE Journal 44 1731-1739. 

Other additives besides blowing agents can be added to foams, to alter the solubility of the gas in the polymer, promote emulsification, promote dispersion of the gas in the polymer or control gas bubble size. 

Another consideration in the case of gas-liquid mixtures is the impact of the impeller on gas bubble size. In an actual stirred tank, the momentum of the rotating impeller often acts to break up gas bubbles as they pass through the region. This reduces the bubble size and can lead to an increase in the gas hold-up as well as a change in the momentum exchange term (drag) between the phases. When experimental data are used, this phenomenon is missing from the formulation but can often be incorporated into the calculation if subroutines, written by the user, are available to modify the model in the commercial software. 

Estimate the gas-bubble size, the gas holdup, the specific interfacial area, and the mass-transfer coefficient for water in the liquid at the gas-liquid surface. 

Properties That Characterize Foam. Foams typically are characterized by quantifying foam quality and bubble size. 2 Foam quality is express as the fraction or percentage of total volume that is gas. Bubble size is specified in terms of average size or diameter (foam texture) and the range of bubble sizes present. 

Figure 3.39 shows the effect of gas bubble size on the oil droplet capture rate. The smaller the bubble size, the greater the chance of capture will be. Typical mean bubble sizes range between 50 and 60 pm. 

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