Gas-liquid mass transfer correlations for

Bubble columns, 15 698-703, 726 estimating shear rates for, 15 689 gas-liquid mass transfer correlations for, 15 70 l-702t... 

Gas-Liquid Mass Transfer Correlations for Conventional Mechanically Agitated... 

TABLE 9.2 Gas-liquid Mass Transfer Correlations for Fixed Bed Reactors... 

A simple approach for finding an appropriate gas-liquid mass transfer correlation is to break ki a down into its components (a and l) and And separate correlations for each, after which those components would be combined to generate a k a correlation. It is very convenient to start with the interfacial area since an applicable theoretical correlation is readily available (Figueiredo and Calderbank, 1979)... 

The scale-up problems arise from the fact that all STR gas-liquid mass transfer correlations are empirical. They are, for the most part, unable to account for hydrodynamic or liquid property changes with scale and time. Extensive attempts have been made in using nondimensional groups, especially toward solving gas-liquid processes involving non-Newtonian liquids. These correlations tend to be more complicated and require numerous static, but only few dynamic, inputs. One of the simplest correlations is presented by Ogut and Hatch (1988), which involves four dimensionless groups and requires six inputs. One of the more complicated forms. 

TABLE 5-22 Mass Transfer Correlations for Falling Films with a Free between Gas and Liquid... 

Gas/Liquid Mass Transfer This topic has been widely investigated for gas absorption in packed beds, usually countercurrent. One correlation for cocurrent flow in catalyst beds is by Sato et al. (First Pacific Chemical Engineering Congre.s.s, Pergamon, 1972, p. 187) ... 

F = Function of the molecular volume of the solute. Correlations for this parameter are given in Figure 7 as a function of the parameter (j), which is an empirical constant that depends on the solvent characteristics. As points of reference for water, (j) = 1.0 for methanol, (j) = 0.82 and for benzene, (j) = 0.70. The two-film theory is convenient for describing gas-liquid mass transfer where the pollutant solute is considered to be continuously diffusing through the gas and liquid films. 

The mass transfer coefficient is expected to relate gas power per unit volume and gas terminal velocity. Measurement of gas bubble velocity is troublesome in the experimental stage of aeration. Extensive research has been conducted for an explanation of the above correlation. Gas-liquid mass transfer in low viscosity fluids in agitated vessels has been reviewed and summarised as stated in (3.5.1.7)—(3.6.2) 3... 

Later publications have been concerned with mass transfer in systems containing no suspended solids. Calderbank measured and correlated gas-liquid interfacial areas (Cl), and evaluated the gas and liquid mass-transfer coefficients for gas-liquid contacting equipment with and without mechanical agitation (C2). It was found that gas film resistance was negligible compared to liquid film resistance, and that the latter was largely independent of bubble size and bubble velocity. He concluded that the effect of mechanical agitation on absorber performance is due to an increase of interfacial gas-liquid area corresponding to a decrease of bubble size. 

Calderbank and Moo-Young (C5) have studied gas-liquid mass transfer in systems characterized by high viscosities and high diffusion coefficients, and have on the basis of data obtained in this and other studies developed correlations for the mass-transfer coefficients. 

The gas-liquid mass transfer for organic solutions and the liquid-solid mass transfer are evaluated using the appropriate correlations (eqs. (3.427) and (3.435), respectively), while the Fogler s overall coefficient (K°A) is (eq. (3.379))... 

Gas-liquid mass transfer in fermentors is discussed in detail in Section 12.4. In dealing with in gas-sparged stirred tanks, it is more rational to separate and a, because both are affected by different factors. It is possible to measure a by using either a light scattering technique [9] or a chemical method [4]. Ihe average bubble size can be estimated by Equation 7.26 from measured values of a and the gas holdup e. Correlations for have been obtained in this way [10, 11], but in order to use them it is necessary that a and d are known. 

Finally, in Fig. 3.4-12 [24], a comparison is given for the overall, gas-based, mass transfer coefficient for several liquid-to-gas and solid-to-gas packed beds and column systems. In Fig. 3.4-12, for a given data point, the vertical distance up to the Tan et al. [27] correlation (which is for a solid-to-fluid boundary layer) would provide a measure of the liquid-side mass-transfer resistance associated with the liquid. This is so because amount of the large gas... 

In this chapter, we study various correlations for gas-liquid mass transfer, interfacial area, bubble size, gas hold-up, agitation power consumption, and volumetric mass-transfer coefficient, which are vital tools for the design and operation of fermenter systems. Criteria for the scale-up and shear sensitive mixing are also presented. First of all, let s review basic mass-transfer concepts important in understanding gas-liquid mass transfer in a fermentation system. 

Gas holdup and volumetric gas-liquid mass-transfer coefficients are correlated with the gassed power input/volume and with the aeration rate (actual gas superficial velocity), e.g., the correlation of van t Riet [Ind. Eng. Chem. Proc. Des. Dev. 18 357 (1979)] for the volumetric mass-transfer coefficient of coalescing and noncoalescing systems ... 

Correlations for gas holdup and the volumetric gas-liquid mass-transfer coefficient can have the general form... 

In many practical applications, gas-liquid mass transfer plays a significant role in the overall chemical reaction rate. It is, therefore, necessary to know the values of effective interfacial area (aL) and the volumetric or intrinsic gas-liquid mass transfer coefficients such as kLah, kL, ktaL, kg, etc. As shown in Section IX, the effective interfacial area is measured by either physical e.g., photography, light reflection, or light scattering) or chemical methods. The liquid-side or gas-side mass-transfer coefficients are also measured by either physical (e.g., absorption or desorption of gas under unsteady-state conditions) or chemical methods. A summary of some of the experimental details and the correlations for aL and kLaL reported in the literature are given by Joshi et al. (1982). In most practical situations, kgaL does not play an important role. 

The volumetric gas-liquid mass transfer coefficient, kLaL, depends upon physical properties such as viscosity, density, and surface tension of liquid. In general, aL oc Pl2/< l6- The coalescence characteristics of the vessel have a pronounced effect on aL and kLaL. The correlation presented by Judat (1982) is recommended for this purpose. Foaming characteristics can also influence kLaL. In general, the use of kLaL = f(P/V, ug) relationship is recommended for a given aerated vessel. The diameters of stirrer and vessel and the heights of stirrer and liquid level also affect kLaL. The work of Calderbank and coworkers in this area is most worth noting. 

The above correlations are recommended for calculations of gas-liquid mass transfer coefficients in conventional stirred slurry reactors. 

In some cases, a slurry reactor with multiple agitation is used. For example, Bern et al. (1976) used the reactor shown in Fig. 15 for the hydrogenation of oils. In this reactor type, horizontal partitions are also introduced at various stages to reduce the extent of backmixing. These authors proposed the following correlation for the gas-liquid mass transfer coefficient, kLaL, in this type of reactor based on pilot-plant data (30 and 500 L capacity) ... 

For gas-liquid-solid systems, studies on gas-liquid and liquid-solid mass transfer in basket reactors have been rather limited. For the rotating basket reactor, gas-liquid mass-transfer coefficient data are needed. Liquid-solid mass transfer has been studied by Teshima and Ohashi (1977), and their data are correlated by... 

For baffled agitators, sparged with submerged impellers, some of the useful correlations for the gas-liquid interfacial area aL and the volumetric gas-liquid mass-transfer coefficient are outlined in Table XXL The correlations are liquid mass-transfer coefficient are outlined in Table XXI. The correlations are valid under nonflooding conditions (i.e., low gas flow rate). 

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