In gas-liquid systems

In gas-liquid systems, the tendency for an increase in the gas superficial velocity upon scale-up can further increase the overall circulation time. 

At any instant, pressure is uniform throughout a bubble, while in the surrounding emulsion pressure increases with depth below the surfaee. Thus, there is a pressure gradient external to the bubble which causes gas to flow from the emulsion into the bottom of the bubble, and from the top of the bubble back into the emulsion. This flow is about three times the minimum fluidization velocity across the maximum horizontal cross section of the bubble. It provides a major mass transport mechanism between bubble and emulsion and henee contributes greatly to any reactions which take place in a fluid bed. The flow out through the top of the bubble is also sufficient to maintain a stable arch and prevent solids from dumping into the bubble from above. It is thus responsible for the fact that bubbles can exist in fluid beds, even though there is no surface tension as there is in gas-liquid systems. 

Mass transfer in the continuous phase is less of a problem for liquid-liquid systems unless the drops are very small or the velocity difference between the phases is small. In gas-liquid systems, the resistance is always on the liquid side, unless the reaction is very fast and occurs at the interface. The Sherwood number for mass transfer in a system with dispersed bubbles tends to be almost constant and mass transfer is mainly a function of diffusivity, bubble size, and local gas holdup. 

Pennemann, H., Hessel, V, Kost, H.-J., Lowe, H., de Belleeon, C., Investigations on pulse broadening for transient catalyst screening in gas/liquid systems, AIChE J. (2003) 34. 

The sulfite oxidation is a recommended test reaction for determining the size of the specific interfacial area in gas/liquid systems, in particular as expressed by the a value [9, 10]. 

Specific interface in gas/liquid systems Mass-transfer coefficient Time-dependent dispersion coefficient Knudscn number Reaction rate constant... 

The intensity of mixing in gas-liquid systems, given by the product of rotational speed and mixing time Nxm, is mainly dependent on the geometrical characteristics of the stirrer and the reactor and can be expressed as ... 

Dukler, A. E., and Y. Taitel, 1991 b, Flow Pattern Transitions in Gas-Liquid Systems, chap. 3 Modeling Two-Phase Annular Flow, chap. 5, and Modeling Upward Gas-Liquid Flow, chap. 7, in Two-Phase Gas-Liquid Flow A Short Course on Principles of Modelling Gas-Liquid Flow and on Modern Measuring Methods, University of Houston, Houston, TX. (3)... 

The flow patterns in liquid-liquid systems have not been as extensively studied as those in gas-liquid systems. However, Russell et al. (R6), and Charles et al. (C3) have studied the flow of oils and water in horizontal pipes and have presented flow-pattern charts for the various oil-water systems. It is very difficult to predict the flow pattern for a liquid-liquid system, unless the liquids have physical properties similar to those of water and the oils used by Govier and co-workers. The Baker chart might be used to give a first estimate of the flow pattern for a liquid-liquid system, but the viscosity of the less-dense phase is not included in the coordinate parameters, and the feasibility of such an approach has never been investigated. 

If the no-phase-change restriction does not rigorously apply, a simple design procedure can be formulated based on the results discussed in Section III, where it is shown that thermal equilibrium is quickly achieved in gas-liquid systems because of the large heat effects associated with evaporation or condensation. Although the total mass transfer between the phases may be small, it is not unrealistic to assume that the gas and liquid phases have the same temperature at each axial position. 

In a single-phase liquid system, pressure can influence an equilibrium only by altering equilibrium constant K. This requires very high pressures (>>1000 atm). The pressures applied in gas-liquid systems are much lower. They range from 1 atm to a few hundred atm. Higher pressures are usually not necessary, since they would not change the concentration of the gas in the liquid phase by very much. 

Aromatic molecules with no polar substituent include benzene derivatives or other, more polyaromatic molecules, such as naphthalene, phenanthrene, and anthracene. These are polarizable. Paraffins are not polarizable by comparison. In gas-liquid systems, aromatic molecules will show stronger interactions with polar stationary phases that paraffins of comparable boiling point and, thus, polar stationary phases can aid in improving separation of substituted aromatics. 

In case of mass transfer accompanied by chemical reactions in gas-liquid systems the mass flux of the absorbed component is usually formulated as the product of an enhancement factor Ea and the mass flux corresponding to physical absorption at the same bulk concentration ... 

Livingston, J., Morgan, R., and Richardson. A.H. Solubility relations in gas-liquid systems. IV. The solubility of oxygen in water as found by an anal3rtical method. J. Phys. Chem., 34(10) 2356-2366, 1930. 

The Contacting Scheme. In gas-liquid systems semibatch and countercurrent contacting schemes predominate. In liquid-liquid systems mixed flow (mixer-... 

Similarly, the superficial velocity v or vq of the gas throughput as an intensity quantity is a reliable scale-up criterion only in mass transfer in gas/liquid systems in bubble columns. In mixing operations in bubble columns, requiring the whole liquid content be back mixed (e.g., in homogenization), this criterion completely loses its validity (10). 

Since the experiments of Tung and Drickamer, the resistance to diffusion through an interface has been further studied in gas-liquid systems by Emmert and Pigford (E2), who studied the absorption and desorption of CO 2 and 02 in water in a wetted-wall tower and interpreted their results in terms of accommodation coefficients. They... 

Andreozzi R, Caprio V, D Amore M G, Insola A, Tufano V (1991) Analysis of Complex Reaction Networks in Gas-Liquid Systems, The Ozonation of 2-Hydroxypyridine in Aqueous Solutions, Industrial Engineering and Chemical Research 30 2098-2104. 

This is the more general type of interaction which may occur in liquid-liquid two-phase systems and in gas-liquid systems where gas is the dispersed phase. 

VAN Swaaij, W. P. M. and Versteeg, G. F. Chem. Eng. Sci. 47 (1992) 3181. Mass transfer accompanied with complex reversible chemical reactions in gas-liquid systems An overview. 

Figure 3.75 Scheme of the screening device in gas/liquid systems [109]. 

Investigations on pulse broadening for transient catalyst screening in gas/liquid systems, AIChEJ. 2003, 50 (8), 1814-1823. 

In transport limited reactions in gas/liquid systems, mass transfer is usually dimensioned according to P/V = idem and v = q/S = idem, see section 10.4.1. In scaling up, these conditions also speak in favor of decoupling the gas supply and... 

Gas/liquid contacting is frequently encountered in chemical reaction and bioprocess engineering. For reactions in gas/liquid systems (oxidation, hydrogenation, chlorination, and so on) and aerobic fermentation processes (including biological waste water treatment), the gaseous reaction partner must first be dissolved in the liquid. In order to increase its absorption rate, the gas must be dispersed into fine bubbles in the liquid. A fast rotating stirrer (e.g. a turbine stirrer), to which the gas is supplied from below, is normally used for this purpose (see the sketch in Fig. 34). 

Bubble columns are important appliances for the absorption of gases in liquids and, consequently, for the execution of chemical reactions in gas/liquid system. In this context, the attainable interface (A sum of the surfaces of all gas bubbles) is of most interest because it affects the mass flow in a directly proportional manner. If a gas throughput q is introduced into a bubble column with the diameter D and the liquid height H, the liquid height rises by the amount occupied by the gas bubbles in the liquid. The gas fraction in the liquid, the so-called gas hold-up H can be determined from the liquid height Hr, of the gassed and the non-gassed liquid (see sketch). 

In gas/liquid/solid sparged columns the situation is somewhat more complicated. Just as in gas/liquid systems, different regimes have to be distinguished. Here the most important variables affecting the axial dispersion coefficient Dc l of the liquid, are dc and uG ... 

Loiseau et al. (1977) found that their data for nonfoaming systems agreed well with Eq. (3.3). Calderbank (1958), Hassan and Robinson (1977), and Luong and Volesky (1979) have also proposed correlations for power consumption in gas-liquid systems. Nagata (1975) suggested that power consumption for agitated slurries can be reasonably predicted from these correlations by the correction factor psi/pL, where psl is the density of the slurry. Power consumption for a gas-liquid-solid system has also been studied by Wiedmann et al. (1980). They examined the influence of gas velocity, solid loading, type of stirrer, and position of the stirrer blades on power consumption plots of power numbers vs. Reynolds numbers for propeller and turbine type impellers proposed by them are shown in Fig. 13. 

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