Page 217 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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connected with the different form and properties of the packings investigated in
the two papers.

3,2.1.2.1.4. Wetted and effective surface area
The effective surface area a e can be considered composed of two
components, effective wetted area of the packing, and surface of the drops and
jets trickling in the packing free volume. In case of small packing elements and
low liquid superficial velocity, the main part of the effective surface is the
effective part of the wetted area ««, of the packing. For small packing elements
the effective wetted surface is only a part of the whole wetted surface area of
the packing. It is because the surface of the immovable liquid, held up in the
packing as static liquid holdup, wets a part of the packing surface, but is not in
contact with the gas phase and therefore not active for the mass transfer
processes. As a result of the investigations carried out up to now, the following
is observed:
Under the loading point the change of the gas velocity does not affect
the effective surface area. Over this point the increasing of the gas velocity
leads to an increase of a e;
The increasing of the liquid superficial velocity leads to an increase of
a e,;
The reduction of the surface tension leads to an increase of the effective
surface area.
The influence of the liquid viscosity on a s is through its effect on the
liquid holdup. At a small liquid holdup its increasing leads to increasing of a e.
At a large holdup its increasing has the opposite effect.
The increasing of lie wettability of the packing material leads to an
increase of the effective surface area,
The increasing of the specific surface of the packing leads to increasing
ct
of the effective surface area and to reduction of the ratio —-.
a
The effect of the packing form is also of importance for a e.

3.2.1.2.1.4.1. Some experimental data
Experimental data for some of the best random packings of metal and
plastic are obtained in [95, 216] by using the method with absorption of CO2 in
NaOH solution, at gas (air) velocity 1 m/s. The geometrical characteristics of
the investigated packings are presented in Table 2.
Parallel to the measurements of the effective surface area, the pressure
drop of the packing is also investigated by using a differential manometer, with
accuracy 0.1 Pa. The column diameter was 470 mm. The height of the packing
in all experiments was 2400 mm. A special liquid phase distributor was used