Page 81 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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trickling in the free volume. According to the dimensional analysis, under the
loading point it can be presented as follows:

L,Re l,Ed,e 0tl 1.JJ , (266)
a

where Bg is the angle of wettability of the packing material, called also contact
angle.
The influence of three important physical parameters on the effective
area of the packing are discussed below. They are the wettability of the packing
material expressed through the angle of wettability, the liquid surface tension,
and the liquid viscosity.

1.6.3.1, Influence of the contact angle ofwettability
The forces responsible for the holding of the liquid phase on the surface
of the packing are the intermolecular adhesion forces. Their effect can be
measured through the angle ofwettability presented in Fig. 12.

solid
Fig. 12. Angle ofwettability

Upon contact of three different phases, solid, liquid and gas (or vapour),
on the phase boundary line, three different boundary surface tensions act. They
are:
1. Boundary surface tension between the liquid and the solid phase a LS,

2. Boundary surface tension between the liquid and the gas phase c^ ,
3. Boundary surface tension between the solid and the gas phase cr SG.
These three boundary surface tensions, the values of which are
dependent on the chemical properties of the phases, the temperature, and the
pressure, are in equilibrium according to the equation of Young [49].

°~m = ^LS + cm B e®w ( 267 )