Page 137 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

132

the mass transfer in the liquid. The effective surface area «e is calculated by the
equation:

— = —M— (48)
a K a {D )
G 0
G
K Ga and D G are the volumetric mass transfer coefficient and the diffusivity of
the absorbed gas or evaporated liquid. K Ga 0 and Do are the corresponding
values for naphthalene sublimation.

2.1.2.5.6. Method using data from evaporation of liquid from completely wetted
packing and from absorption of very soluble gases
The method [33, 34] is similar to that given above. The difference is
that instead of naphthalene sublimation, the experiments are performed with
evaporation of liquid soaked in a packing made of porous material.

2.1.2.5.7. Method for determination of the effective surface area from data
obtained in a packed bed column and a laboratory column with spheres
The method is developed in two variants differing in the kind of the
laboratory column used. In the first one, this is a column with a single sphere
[35, 36], and in the second - with a vertical column of spheres [37]. In both
cases the mass transfer process is liquid-side controlled absorption. The method
accepts that the mass transfer coefficients in a packing and on spheres are the
same, and that the effective surface of the spheres is equal of their geometrical
surface. Because the mass transfer coefficient depends on the hydrodynamics of
the liquid phase, and the hydrodynamics - on of the form of the packing, the
first acceptation is doubtful.

2.1.2.5.8. Method of Danckwerts
The method of Danckwerts [38, 39] is based on the fact that in ease of
absorption controlled by a fast chemical reaction in the liquid phase, the mass
transfer coefficient is independent of the gas and liquid phase hydrodynamics. It
can be calculated by the equation:

k r= (nD)™ (49)

kr is the mass transfer coefficient in absorption controlled by a first or pseudo-
first order fast chemical reaction, in m/s;