Page 234 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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4 u M UM
a e = 2.944.10 v L L (111)

m om
a e=O.165J.v° L L (112)

Simple calculations show that the effect of the viscosity change in the
investigated area for the first equation is only 6.25%, and for the second -22%,
This small effect and the absence of error estimation make this equation not
reliable for industrial calculations.
It is proposed in [24] to use the angle of wettability as a criterion for the
wettability. Simple experiments carried out by us with the investigated metal
packings show that no drops are formed on the packing surface area treated
preliminary with NaOH solution. That is why the angle of wettability is zero
and should not be taken into account in the equation for calculating the effective
surface area of the studied packings. Some investigations [45-48, 88-90] show
that the effect of the surface tension on the effective surface area of the packing
is significant and must be taken into account. Theoretically there is no base to
eliminate the effect of the viscosity. The effect of the liquid density is
important. Having in mind that a part of the packing surface area can be wetted
independently of the liquid superficial velocity, and using the ir-theorem, the
following equation in dimensionless form is obtained [95]:

l
^ = K o + K ]Eo F^(a.d pf, (113)

where Kg, Ki, I, n, and/? are experimental constants;

Ed = ' - Eotvos number;
a <J

Fr L = Froude number;
E
3
pi- liquid density, kg/m ;
2
3
a- specific surface of the packing in m /m ;
a- liquid surface tension in N/m;
3
2
L- liquid superficial velocity in m /(m s);
dp- nominal packing diameter in m.
After determining the experimental constants K§, Kj, I, n, and p from
the experimental data, Eq. (113) obtains the form;