Page 59 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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3
C Gin- the concentration of the absorbed gas in the gas phase in kmol/nm inert
3
gas and in kmol/m ;
2
3
a s - effective surface area in m /m ;
c p and c L - the specific heat of the gas and the liquid phases in J/(kgK);
3 2
L- liquid superficial velocity in m /(m s);
f - the heat of absorption in J/kmol;
t G and t t - temperature of gas and liquid in °C;
N - number of absorbed components;
i - index for the absorbed component.
To the balance equation above the following equations must be added:
- Eq. (131) for additive interfacial resistance;
- equation for calculation of the effective surface area a B;
- equations for calculation of the partial mass transfer coefficients k G and fa;
- equations for determination of the equilibrium and of the physical properties
of the two phases.
In case of absorption accompanied by chemical reaction Eq. (133) is
transformed into:

where K is an enhancement factor, coefficient of acceleration due to chemical
reaction. The methods of its calculation are given in Chapter 5. In details they
are presented through examples in the books by Danekwerts [19] and Astarita
[20].
In case of simultaneous mass and heat transfer processes, for example
when cooling of flue gases containing water vapours for utilization of their heat,
or in case of packed bed cooling towers, the piston flow model can be written as
follows:
The basic equation of mass transfer (evaporation and condensation):

G hdx h /dh = Kca e (C G -C G*); (170)

The basic equation of heat fransfer: