Page 136 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

131

from dry packing, and second from irrigated packing. In both cases the
sublimation is a gas-side controlled process. In the first case the whole surface
area of the packing takes part in the mass transfer, in the second - only not
wetted surface.
From the data for the volumetric mass transfer coefficient, respectively
in the first case (Kcia) and in the second case (Kasd), the wetted surface area
can be obtained.

K rta a-a, , a,
—^— = •- = !—•- (46)
K G2a a a

2.1.2.5.4. Method of van Krevekn
The effective surface area according to this method [27] is determined
based on the assumption that over some value LQ of the liquid superficial
velocity, the volumetric mass transfer coefficient, in case of a gas-side
controlled processes at a given gas velocity, is no more depending on L, and a e
is equal to the specific surface area of the packing. Assuming that Kg of the
irrigated packing is not depending on L, from the assumption above it can be
written:

*-•£"*- . (47)
a K Ga h

where K Ga L is the value of KQO at Lg.
The main assumption of the method is true only for a packing with
vertical walls made of very wettable material. That is why recently the method
is used only in that case [28-30].

2.1,2.5.5. Method using naphthalene sublimation and gas-side controlled
absorption process
The method is presented by Shulman et al. [31] and successfully used
also by Zhavoronkov et al. [32]. According to this method the experiments are
carried out in two stages, first, naphthalene sublimation, and, second, gas-side
controlled process, for example absorption of NH3 in a dilute solution of strong
acid or of SO2 in solution of NaOH. In both cases the concentration of the
reactant in the liquid phase is not lower than 0.3 N to prevent the influence of