Page 231 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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To calculate the effective surface area of Rasehig rings with diameters
from 15 to 50 mm using data of Fumitake [101] obtained after the method of
Danckwerts, and data of Zhavoronkov [87] obtained after the method of
Shulman, the following equation is proposed [102]:

0 m
m
s
^ = QJ44.Fr L Eo" Re? (a.dr. (104)
a
Later using own date obtained by the method of Danckwerts and also
data from the literature, Kolev proposed the equation [105]:

43
a/a=0.583[p Lg/f^ ajf^Fr^fa df , (105)

2 3
where Fri=L a/g is the Froude number; /%- liquid density, kg/m . The date used
for obtaining the experimental constants of this equation are presented in Table
14.
The effective surface area of the polypropylene Intalox Saddles 50.8
mm obtained by Danckwerts and Rizvi [108] is significantly smaller than that
predicted by Eq. (105). The reason is that this material is very poorly wetted and
the wettability of the material is not token into account in this equation.
An equation showing similar influence of L, a and a is presented also
by Billet and Schultes [237, 316]

0J
75
6 45
2
St = l,5(a.d h)- .R ef Wet Fr- - . (106)
a
According to equations (105) and (106) the predicted a/a as a function
of X in double logarithmic coordinates is a straight line.
Equation (106) is valid for neutral and positive systems for which no
Marangoni effect exists. In case of negative system for which the surface
tension along the column decreases from top to bottom, the Marangoni effect
must be taken into account. More information about the physical nature of this
effect is presented in Chapter 4. For correction of the value of k L in case of
negative systems Billet and Schultes [316 5 322] presented the equation: