Page 229 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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Ramm [96, p.446] proposed the expression:

AL
a.- — . 000)

where A and B are experimental constants. For Raschig rings and saddles 25-50
mm, A=%5 and 5=0.00125. The accuracy of the equation is ±25%. For 50 mm
Raschig rings, it is better to use .4=83.5 and ,6=0.00067. It is surprising that the
influence of the specific surface area of the packing is not taken into account in
this equation. This can be explained only with the small interval of changing of
this value.
Using data obtained with the method described in 2.1.2.5.7., Hikita,
Kataoka and Nakanishi [99] obtained the equation:

l a m , (101)
a

where m = bd" . The value of a in this equation is in mN/m. d is the packing
element diameter, m.
The values of the constants A, bandp are as follows:
A B P
Rings 2.26 1.83 0.48
Saddles 0.707 0.495 0.98

Because of some shortcomings of the method for obtaining the
experimental constants, discussed in 2.1.2.5.7., this equation is not to be
recommended.
Another equation for calculation of the effective surface area of random
packings is suggested by Onda et al. [92]:

0M
75
0J
OJ
f- Re L Ff We J, (102)
L
where Re L = ' is the Reynolds number; Fr = —— - Froude number; We
o-Mi 8
3
= L fi/(er.a)- Weber number; a- surface tension in N/m; and a^ critical surface
tension at which the wettabiliry angel is zero. Principally this equation is unable