Correlations for Gas Holdup

Some important investigations and the correlations for gas holdup given therein are listed in Table 7A.1. 

Equation 7A.12 was shown to uniquely represent a very large number of literature data covering wide variety of impellers and impeUer-vessel combinations. The major feature of Yawalkar et al. s approach is that (i) it is based on sound logic and (ii) requires variables and wm) that are readily estimated and measured, respectively, as compared to turbulence parameters, which represents (Section 7A.3). The value for the correlation of the type represented by Equation 7A.12 was 0.9, 

The relatively better fit of Equation 7A. 13 is obviously due to inclusion of additional parameters. However, the differences between the predictions of Equations 7A.12 and 7A.13 are not significant. For example with T=2 m, DIT=033, wm=0.1, and N/N =l.l, Equation 7A.12 predicts -q=0.22, whereas Equation 7A.13 yields eQ-0.25. This difference of -15% between the two predictions of Equations 7A. 12 and 7A.13 should be acceptable within the limits of experimental errors. Both Equations 7A.12 and 7A.13 are simple to use and the choice of one of them is a matter of convenience. When a relatively accurate estimate is desired. Equation 7A.13 should be used. 

The aforementioned correlations for the gas holdup require knowledge of N. Hydrodynamics in two- and three-phase reactors has been widely investigated as discussed in Sections 7A.3 and 7A.4, respectively. Various investigators have reported reliable correlations for over a wide range of geometric configurations and operating 

Six-blade 45° downflow pitched turbine (Rewatkar and Joshi 1993)  

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More recent literature regarding generalized correlational efforts for gas holdup is adequately reviewed by Tsuchiya and Nakanishi [Chem. Eng Sci., 47(13/14), 3347 (1992)] and Sotelo etal. [Inf. Chem. Eng., 34(1), 82-90 (1994)]. Sotelo et al. (op. cit.) have developed a dimensionless correlation for gas holdup that includes the effect of gas and liquid viscosity and density, interfacial tension, and diffuser pore diameter. For systems that deviate significantly from the waterlike liquids for which Fig. 14-104 is applicable, their correlation (the fourth numbered equation in the paper) should be used to obtain a more accurate estimate of gas holdup. Mersmann (op. cit.) and Deckwer et al. (op. cit.) should also be consulted. 

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

More recent correlations for gas holdup and mass transfer include the effect of pressure and bimodal bubble size distribution (small and large bubbles), in a manner analogous to the treatment of dilute and dense phases in fluidized beds [see, e.g., Letzel et ah, Chem. Eng. Set, 54 (13) 2237 (1999)]. 

Summary of Correlations for Gas Holdup in Mechanically Agitated Reactors (Low... 

Takriff et al. have presented correlations for gas holdup in MSAC. Their correlation is presented in graphical form as Figure 10.43 and the equation of the graphical fit of the correlation is ... 

Prakash and Bendale (10) have undertaken an extensive literature search on gas holdup and dispersion correlations in slurry bubble column reactors. They tested various correlations for the estimation of gas holdup against experimental data and found that the average absolute relative error varied from 12 to 165%. These large errors are primarily due to the fact that literature correlations for gas holdup are based on constant gas velocity along the column height. In reality. 

In contrast, an industrial design has several choices. First and most complicated would be to use the experimental approach, which would be very intensive and costly. Second, a simplified correlation for gas holdup and gas-liquid mass transfer coefficient could be used ... 

Reilley, I.G., Scott, D.S., De Bruijin, T., Jain, A., and Pixkorz, J. (1986), A correlation for gas holdup in turbulent coalescing bubble columns, Canadian Journal of Chemical Engineering, 1986(64) 705-717. 

TABLE 7A.1 Correlations for Gas Holdup in Stirred Tank Reactors Available in the Literature... 

Behkish A, Lemoine R, Oukaci R, Morsi BI. (2006) Novel correlations for gas holdup in large-scale slurry bubble column reactors operating under elevated pressures and temperatures. Chem. Eng. J., 115 157-171. 

Godbole et al. [42] proposed the following correlation for gas holdup in non-Newtonian fluids in a bubble column ... 

Chen et al. [1999] derived correlations for gas holdup, turbulent eddy diffusivity, and liquid recirculation velocity from measurements in a bubble column with a diameter of 0.45 m. 

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