Mass-transfer coeffident

Figure 7.16 Estimated wall concentration of (A) cakium and (B) humic add (HA, 10 kDa) as a function of flux and mass transfer coeffident ((M) epical of stirred cell ( O A typical of crossflow or spiral element).

Nusselt s numbers, which are functions of numbers Re and Pr, are used for definitions of heat transfer and mass transfer coeffidents. 

The mass transfer coefficients in the crossflow cell were estimated from independent measurements of dissolution of a plate of benzoic acid into water at two different crossflow rates 50 L h and 120 L h , at 30 °C. Mass transfer coefficients for docosane and TOABr were estimated based on the experimentally measured benzoic add mass transfer coefficients values and the Chilton-Colbum mass transfer coeffident correlation. Details of the procedure applied are described elsewhere [32]. 

The mass transfer coeffidents calculated for docosane and TOABr, using the Chilton-Colbum correlation, are presented in Tab. 4.2. 

Although all of the mass transfer coeffident data available in the hterature are for aqueous systems and most are for ultrafiltration [46—49], the values are in the same order of magnitude as those obtained in these experiments -10 m s , indicating that the technique used gives reasonable estimates. 

Like their random-peuiking efficiency model (above), the Bravo, Fair et al. structured-packing model is ba on the two-film theory. The HTU is calculated from the mass transfer coefficients and interfacial areas using Eqs. (9.23) and (9.24). The HETP can be calculated from the HTU using Eqs. (9.12) and (9.13). The mass transfer coeffidents are evaluated from... 

To measure the liquid film mass-transfer coeffident k a, a system for absorption or desorption of very insoluble gases such as Oj or CO2 in water is used. The experiment gives K a, which equals k a, since the gas-phase resistance is negligible. 

In the present state of development, at least for the random packings, it is prudent to deal widi an effective mass transfer surfoce , as used by Bravo and Fair, that can be deduced by semiempitical means, or simply to couple die area term with the mass transfer coeffident to form a volumetiic-lype coefficient. 

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