Page 233 - Packed bed columns for absorption, desorption, rectification and direct heat transfer
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where HTUi is the height of a mass transfer unit for the liquid phase;
HTUOL- overall height of the mass transfer unit calculated for the liquid phase;
x and x* - mol concentration and mol equilibrium concenixation of the liquid
phase.
The first term in the Marangoni number describes the change of the
surface tension with the concentration along the column, while the expression x-
x* takes into account the concentration difference in the boundary layer.
For calculation of the effective surface area at the flooding point (fly?),
Billet and Schultes [316,322] presented the equation:
-0.45
, (109 )
where c w is the surface tension of the water in N/m.
The usage of cr w for calculation of the effective surface of a packing
operating at a system with different properties is not theoretically grounded, but
is applied by some investigators to obtain a formally dimensionless equation.
For determination of the effective surface area between the loading and
the flooding points, ay ft Billet and Schultes [316] presented the following
equation:
(110)
a a \ a
In the most of the investigations on the effective surface area it is
assumed that this value is practically independent of the liquid viscosity. To fill
up this gap, Rizzuty and Brucato [217] carried out investigations with 10 mm
6
Raschig rings using sugar solution with kinematic viscosity from 1.24X10" to
1
6
2.3x10" mV . In the experiments a variant of the method of Danckwerts is
used, namely absorption of carbon dioxide in potassium earbonate-biearbonate-
arsenite solutions. It is obtained that at kinematic viscosity lower than 1.54x10"*
1
mV ; the increasing of the viscosity leads to increasing of the effective surface
area too. The additional increasing of the viscosity leads to decreasing of the
effective surface. Both effects are to be expected theoretically, Chapter 1,
paragraph 1.6.3.3. The following two equations are obtained for each of the
above mentioned intervals of viscosity:
