Page 239 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

229

— (123)
e-H t

Using a radioactive experimental method, Richter [126] obtained the
equation:

s-0.7
r \I-95 s „
[ T" TSSH ir ^ ™ (124)

The equation shows that two times increasing of the column diameter
leads to about four times reduction of the Peclet number, respectively to about
four times increasing of the coefficient of axial mixing in the gas phase.
Because the influence of the column diameter is connected first of all with the
wall effect which is smaller in bigger columns, such an effect is not to be
expected.
Burghart and Bartelmus [332] presented the equation:

m La3K au
Pe m = 3.3Re£ jor "'" . (125)

Dunn et al. [202] developed empirical Peclet number correlations for
both phases. They found that the gas mixing decreases with increasing of the
liquid or gas rates.
Macias-Salinas and Fair [203-205] investigated the axial mixing in
both, gas and liquid, phases for 25.4 mm ceramic Raschig rings and 25.4 mm
metal Pall rings at water - air countercurrent flow in a column with a diameter
of 430 mm, using tracer method. The experimental date as a function of the gas,
respectively of the liquid, mass velocity are presented in Fig. 31 and 32. The
value Hi in the figures is the test length, i.e. the distance between the sensors in
the packing. In the same figures data for the structured packings Sulzer BX and
Flexipac 2 are also presented.