Page 276 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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where the local pressure drop coefficient § is a function of the void fraction e,
H/h accounts for the number of local pressure drops for a given height of the
packing H.
After using the dimensionless pressure drop W, Eq. (162), and Eqs.
(167), (168) and (169) and determining the necessary experimental constants,
the following equation is obtained [163]:

= 0.06\— I e**+!&%** (170)
d
\ J

The precision of the experimental constants at 95 % statistical confidence is
given below:
0.060± 0.0076; 7.00 ± 0.075; -3.8 ± 0.37; -0.64 ± 0.035.
From equations (167)-(170) it follows:

d h 2e 3 G d h e 2

^ ew 0p G. (172)
h

For determination of the experimental constants in Eq. (170), the
experimental data for the packings presented in Table 26 are used. It was
mentioned [163] that the results of Johnstone and Singh [157] for grid packings
were not used, since in [157] there was no information about the packing void
fraction. The void fraction in [160] was calculated using the equation:

e= d/(d ss + dj , (173)

where da is the thickness of the grid boards and d t is the distance between two
neighbouring boards. It is evident that the above equation is valid only when the
length of the apparatus wall perpendicular to the boards is divisible by the sum
of dgg and df, or when it is many times higher than that sum. The power of s in
Eq. (170) is rather high, which requires a precise determination of e.