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The effective mass transfer area is given by a, - a,a0 5 H-°A(CaL Re0)°

where

The transfer units for each phase are calculated from

The overall HTU is given by

where A. is given by Eq. (9.13). HETP can be calculated using Eq. (9.12).

Some data relevant to the application of Bravo and Fair's correlation are tabulated in Table 9.1. Note that the ap values used in deriving this correlation are slightly different from those used by Billet and Schultes (Table 8.2).

Bravo and Fair (122) statistically analyzed the reliability of their model. They concluded that multiplying an HETP calculated from their model by a safely factor of 1.6 will give 95 percent confidence that the column is not too short. This factor is slightly lower than the Bolles and Fair (55,96) and the Onda et al. (123) correlations. MacDougall (58) repeated the statistical analysis after he rearranged the data bank, and showed that a safety factor of 1.3 is more appropriate, making the Bravo and Fair correlation much better than the others.

The Bravo, Fair et al. correlation for structured packing. Bravo, Rocha, and Fair (124) developed the first published fundamental model for structured-packing efficiency. This model was developed for the Sulzer BX wire-mesh packing, but has recently (25,50) been extended to corrugated-sheet packings.

Like their random-packing efficiency model (above), the Bravo, Fair et al. structured-packing model is based 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 coefficients are evaluated from

TABLE 9.1 Data Ba»» and Rang» of Application lor the Bravo and Fair (122) Random Packing Efficiency Correlation

1. ap values used in correlation for packings included in data bank

Size, inches

Packing_Material_Vi_%_V._1_1J5_2_3

TABLE 9.1 Data Ba»» and Rang» of Application lor the Bravo and Fair (122) Random Packing Efficiency Correlation

1. ap values used in correlation for packings included in data bank

Packing_Material_Vi_%_V._1_1J5_2_3

Raachig rings

Ceramic

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