Page 274 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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where the friction coefficient JLj for ceramic Raschig rings is equal to 0.0057. It
is easy to calculate that at s > 0,905, the second term of equation (163), is
negative which means that the equation is not valid in this area of e.
Leva [29,162] suggested the equation:

(164)

where «/ is an experimental constant depending on the packing type and
dimensions.
Another disadvantage of equations (163) and (164) is that they do not
take into account the influence of the Reynolds number.
To calculate the pressure drop of the dry packings with verticals walls,
the following two equations are also proposed [160]:

O5 3M ojm
r = O.59(h/d hr e- Re G (165)

Ji
= (37/Re G +0.113/Re" )(h/d h)-° ' £~ 3M (166)

Both equations are obtained using experimental data for 29 different
packings, like hurdle packing, Raschig rings, rings with a cross, and honeycomb
packing presented in Fig. 53. The geometrical characteristics of the packings are
changed as follows:
2 3
d k = 12.9 to 113 mm; k= 25.4 to 406.4 mm; «=32 to 190 m /m ; e =0.725 to
3
3
0.90 m /m .
The arithmetic average deviation for both equations is 11%. The
average square deviation for 80% of the experimental points is less than 15%.
The comparison of these equations with experimental data for a packing
of thermopressed plates, obtained later, with a higher value of the free volume
shows that their accuracy in this case is not high enough. The experiments show
that the form of equations (165) and (166) is good enough only when the value
of the part of the column cross-section, (1-e), occupied by the packing material
does not change very much. When the difference in (1-e) is larger the
compensation is no more possible and the equations should have different better
physically grounded form. That is, to take into account that the pressure drop of
such kind of packings consists of pressure drop of friction and pressure drop
because of the gas velocity changing at the place of touching of neighbour rows
(local pressure drop).