In air-water systems

Airlift loop reactor (ALR), basically a specially structured bubble column, has been widely used in chemical industry, biotechnology and environmental protection, due to its high efficiency in mixing, mass transfer, heat transfer etc [1]. In these processes, multiple reactions are commonly involved, in addition to their complicated aspects of mixing, mass transfer, and heat transfer. The interaction of all these obviously affects selectivity of the desired products [2]. It is, therefore, essential to develop efficient computational flow models to reveal more about such a complicated process and to facilitate design and scale up tasks of the reactor. However, in the past decades, most involved studies were usually carried out in air-water system and the assumed reactor constructions were oversimplified which kept itself far away from the real industrial conditions [3] [4]. 

Deviations from the theories tend to occur at large Q where the frequency of bubble formation becomes essentially independent of Q, whereas theory predicts / oc For example, the frequency in air-water systems levels out... 

PARTITION COEFFICIENTS OF COMMON FLUIDS IN AIR-WATER SYSTEMS... 

In practice, the changeover can be achieved by adding a surfactant to the water/oil or water/air interface. It enhances both interfacial surface potentials and tends to make them equal (i.e. n(D) for similar surfaces > n(D) for dissimilar surfaces) and it lowers the surface tension of the drop. This type of behaviour has been observed in a variety of systems (see Figure 4.4), including oil/water [54,56,62,63] systems where the addition of surfactant prevented jump-in and in air/water systems where the addition of surfactant decreased (and sometimes eliminated) jump-in distances [5,46,48,49]. 

Many equipment possibilities exist for gas-liquid operations. They are outlined in Table 1 with their main operational characteristics (at least in air-water systems) presented in Table 2. However, the remainder of this section will deal exclusively with agitated vessels containing low-viscosity liquids in which turbulent flow is achieved Re = > --lO )-... 

To solve (9.25) sufficient initial conditions are required. In the work of Prince and Blanch [92] a rough estimate of the initial thickness of the films created in air-water systems was given to be /iq = 1 x 10 (w). Likewise, the final film thickness was taken as /i/ = 1 x 10 (m). 

Figure 13. The mercury cycle in air-water system Winfray and Rudd. 1990).

The wall shear term in Eq. (4.10) is usually neglected for semibatch bubble columns (Su and Heindel, 2003,2004,2005a Su et al., 2006 Ueyama et al., 1989 Zahradnik et al., 1997). For cocurrent bubble columns and airlift reactors, this term is small at low superficial liquid velocities (e.g., I/l 1 cm/s in air-water systems). When the wall shear term is negligible, Eq. (4.10) can be simplified to... 

These issues, positive and negative, are reflected in the available correlations. These correlations are both highly useful and also limited. Some are useful because the inputs are easily measured and adjusted as needed however, correlations are mostly empirical or semi-empirical, which means that they are not widely applicable but, rather, are bioreactor design dependent at best. Hence, geometric similarity is very important. Furthermore, most studies are performed in air-water systems while most industrial processes use much more complicated and time-variant liquids. In other words, the airhft bioreactor correlations have similar problems as those for stirred-tank bioreactors and bubble columns and are due to the fact that they share the problem source bubble-bubble interactions. Bubble-bubble interactions are highly variable and lead to hydrodynamics which, in turn, are difficult to quantify and predict. Hence, the result has been that the airlift bioreactor correlations and models are either system dependent or not adequately constrained. 

The role of laminar/turbulent flow regime transitions in determining the SS/SW transition has been demonstrated via the variation of tube diameter in air-water systems. Clearly, the same basic phenomena are expected due to variations of the physical properties of the phases when dealing with various two-fluid systems. 

Bubbles in gas-solid fluidized beds usually are sphe-rical-capped as shown in Fig. 9 with the included angle equal to 240° found by experiments as compared to 120° derived theoretically. The bubbles in air-water systems have an angle of 100°. 

Fig. 2.22 Shape of bubbles visualized with a high-speed video camera in air-water system...

The use of molal humidity as the mass-transfer driving force is conventional and convenient because of the development of humidity data for, especially, the air—water system. The mass-transfer coefficient must be expressed in consistent units. 

For the air—water system, Lewis recognized that Cf = hg/ ky based on empirical evidence. Thus, the adiabatic saturation equation is identical to the wet-bulb temperature line. In general, again based on empirical evidence (21),... 

The integration can be carried out graphically or numerically using a computer. For illustrative purposes the graphical procedure is shown in Figure 5. In this plot of vapor enthalpy or FQ vs Hquid temperature (T or T, the curved line is the equiHbtium curve for the system. For the air—water system, it is the 100% saturation line taken direcdy from the humidity diagram (see Fig. 3). 

A water-reducible coating or resin is one that is diluted with water before use. Water-reducible alkyds give comparable drying performance to solvent-bome alkyds. However, they are not widely used because film properties tend to be poorer than those of solvent-bome alkyds, especially in air-dry systems (26). This is pardy because of alcoholysis of the alkyd by primary alcohols such as 1-butanol [71-36-3] C H qO, a common solvent in water-reducible alkyds (27,28) secondary alcohols such as 2-butanol [78-92-2] C qH O, minimize this problem (27). In any case, the slow loss of amine or ammonia leads to short-term high sensitivity to water. Even in the fully dry films, the presence of unreacted carboxyHc acid groups leads to films having comparatively poor water resistance limiting their usehilness. 

U. Single water drop in air, liquid side coefficient / jy l/2 ki = 2 ), short contact times / J 1 lcontact times dp [T] Use arithmetic concentration difference. Penetration theory, t = contact time of drop. Gives plot for k a also. Air-water system. [lll]p.. 389... 

Many experimental studies of entrainment have been made, but few of them have been made under actual distillation conditions. The studies are often questionable because they are hmited to the air-water system, and they do not use a realistic method for collecting and measuring the amount of entrainment. It is clear that the dominant variable affecting entrainment is gas velocity through the two-phase zone on the plate. Mechanisms of entrainment generation are discussed in the subsection Liquid-in-Gas Dispersions. ... 

FIG. 14-53 Pressure for metal Intalox saddles, sizes No, 25 (nominal 25 mm) and No, 50 (nominal 50 mm). Air-water system at atmospheric pressure, 760-mm (30-in) column, hed height, 3,05 m (10 ft), L = liquid rate, kg/(s-m ). To convert kilograms per second-square meter to pounds per hour-square foot, multiply hy 151,7 to convert pascals per meter to inches of water per foot, multiply hy 0,1225, (Coutiesy Notion Company, Akron, Ohio.)... 

FIG. 14-54 Pressure drop for Flexipac packing, sizes No, 1 and No.. 3, Air-water system at atmospheric pressure. Liquid rate in gallons per minute-square foot. To convert (feet per second) (younds per cubic foot) " to (meters per second) (kilograms per cubic meter) " , multiply by 1,2199 to convert gallons per minute-square foot to pounds per hour-square foot, multiply by 500 to convert inches of water per foot to millimeters of water per meter, multiply by 83,31 and to convert pounds per hour-square foot to kilograms per second-square meter, multiply by 0,001.356, Coutiesy Koch Engineering Co., Wichita, Kansas.)... 

In work with the hydrogen chloride-air-water system, Dobratz, Moore, Barnard, and Mever [Chem. Eng. Prog., 49, 611 (1953)] using a cociirrent-flowsystem found that /cg (Eig. 14-77) instead of the 0.8 power as indicated by the Gilliland equation. Heat-transfer coefficients were also determined in this study. The radical increase in heat-transfer rate in the range of G = 30 kg/(s m ) [20,000 lb/(h fH)] was similar to that obsei ved by Tepe and Mueller [Chem. Eng. Prog., 43, 267 (1947)] in condensation inside tubes. 

Hydraulic (Pressure) Nozzles Manufacturers data such as shown by Fig. 14-88 are available for most nozzles for the air-water system. In Fig. 14-88, note the much coarser solid-cone spray. The coarseness results from the less uniform discharge. 

One of the primary concerns of all power plants is to ensure high electricity production and reduce hazardous and waste substances. In that way green electricity could be produced. It is essential to monitor the presence and movement of impurities in various measuring sites in air, water and soil [1]. The presence of hazardous species in these eco-systems, even at low-mg/1 levels, has negative effects for nature and human beings [2, 3]. 

Figure 24. Example of flow pattern map for air water system in horizontal pipes.

Generally, this style of unit will remove particles of 12 to 15 microns efficiently. The typical droplet separator is shown for an air-water system in Figure 4-17A. This will vary for other systems with other physical properties. The variations in capacity (turndown) handled by these units is in the range of 3 to 6 times the low to maximum flow, based on k values [33]. 

Packing iactors determined with an air-water system in 30" I.D. Tower. 

An existing lO-in. I.D. packed tower using 1-inch Berl saddles is to absorb a vent gas in water at 85°F. Laboratory data show the Henry s Law expression for solubility to be y = 1.5x, where y is the equilibrium mol fraction of the gas over water at compositions of x mol fraction of gas dissolved in the liquid phase. Past experience indicates that the Hog for air-water system will be acceptable. The conditions are (refer to Figure 9-68). 

Figure 9-73 presents some of the data of Fellinger [27] as presented in Reference 40 for Hqg for tho ammonia-air-water systems. This data may be used with the Sherwood relations to estimate Hl and Hg values for other systems. 

Moisture may be removed from air by passing it over a surface which is colder than its dewpoint (see Figure 24.9). In air-conditioning systems this is a continuous process, providing that the moisture condenses out as water and can be drained away. If the apparatus dewpoint is beIowO°C, the moisture will condense as frost, and the process must be interrupted from time to time to defrost the evaporator. 

Viswanathan et al. (V6) measured gas holdup in fluidized beds of quartz particles of 0.649- and 0.928-mm mean diameter and glass beads of 4-mm diameter. The fluid media were air and water. Holdup measurements were also carried out for air-water systems free of solids in order to evaluate the influence of the solid particles. It was found that the gas holdup of a bed of 4-mm particles was higher than that of a solids-free system, whereas the gas holdup in a bed of 0.649- or 0.928-mm particles was lower than that of a solids-free system. An attempt was made to correlate the gas holdup data for gas-liquid fluidized beds using a mathematical model for two-phase gas-liquid systems proposed by Bankoff (B4). 

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