Page 273 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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3.2.2.1.2.1.2. Equation for determination of the pressure drop

3.2.2.1.2.1.2.1. Pressure drop of dry packings
Based on own data for a hurdle packing made of wood boards,
Johnstone and Singh [157] offered an equation including the dimensions of the
boards and the distance between them, which is proper only for this packing.
Zhavoronkov, based on data for hurdle packings with boards cogged in
their bottom part, and for arranged ceramic Raschig rings, obtained [158] the
equation:

0.78+ 4.25 d t/h

where h is the height of the packing elements;
F a- maximal free cross-section of the packing, equal to the free volume;
Fj- minimal free cross-section of the packing in the plain of touching of two
neighbour rows.
The dimensionless pressure drop iff is defined as follows:

AP od h
2Hp G(w 0/ef

4.25 d h fh _ _ om
G
The term iff=-z v"i"7 takes mto account the pressure drop
between the packing rows. From this term it follows [159] that the increasing of
F af F b leads to decreasing of the pressure drop. That is, when both free cross-
sections are equal, the pressure drop is maximal, which cannot be true. The
explanation of this error is as follows [160]. The experimental data of
Zhavoronkov for hurdle packings are obtained with boards cogged at their
bottom part. This cogging is not taken into account in calculating Fi,.
Ramm and Sakgeim [159] proposed the equation:

.. . 1.235 2.6)d h
1.16 + — M-, (163)
e si n