Page 78 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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packing size. Such equations are also presented in Chapter 3. Usually their
precision is higher than that of the equations of wider validity. Their
disadvantage is that, especially in case of random packings, such very important
values as specific surface area and void fraction depend not only on the packing
construction and dimensions but also on the dumping of the packing in the
column. That is why their constants, at which they have their higher precision,
are obtained not only for a given size of the elements, but also for a given
specific surface area and void fraction. It is well known, for example, that the
pressure drop of random packings varied from experiment to experiment about
10% only because of the refilling of the packing. Without refilling the
difference in parallel experiments, at least under the loading point, is not more
than 1%.
Since there is information general for the most of the dimensionless
equations for one performance characteristic of different packing types, it is
useful to gather this information in one place which is done in this part of the
book.
1.6.1. Pressure drop

1.6.1.1. Pressure drop of dry packing
The most of the equations for calculation of the pressure drop of
irrigated packings need knowledge for the pressure drop of dry one. The main
form of the equation is:

W = f(Re ,eJ .JJ, (258)
G
i

where y/ = —-—^—r- is the dimensionless pressure drop, often called Euler
H.p G.w 0
number (Eu);
W A
Re G = °" "^° - Reynolds number;
3
p G - gas density in kg/m ;
ju G - dynamic gas viscosity in Pa.s;
e - free column cross-section, equal to the free volume of the packing;
//.../„- dimensionless geometrical parameters of the packing.
In some cases to Eq. (258) as a dimensionless geometrical parameter,
the so called way factor (Fi) offered by Kast [28] can be added. This factor is