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P. 165
Else_AIEC-INGLE_cH003.qxd 7/13/2006 1:45 PM Page 161
3.6 T o-Phase Fix w ed Beds 161
where:
f the Fanning friction f dimensionless , actor
L the length of the distrib m , utor
D the diameter of the distrib m , utor
u i the velocity of the liquid in the inlet of the distrib m/s , utor
the fluid density kg/m , 3
K the resistance coef dimensionless icient, f
p the pressure drop , P a.
The f actor K is considered to be 0.5 for this type of distributors (Feintuch, 1977). The
actor Fanning friction f f for Re D 4000 is calculated using the Churchill equation (Perry
and Green, 1999):
0.9
1 0.27 D 7
4lo g (3.339)
f D Re D
where is the roughness of the material of the distributor in (m), having a value 0.046
D
/
mm for common iron pipes. In any case, the relationship Re D – f – D can be used (Perry
and Green, 1999).
The mean pressure drop at the openings p o (in Pa) is
1 u o 2
p o 2 (3.340)
C 2
Ko
where:
C Ko the opening exit f actor
u o the aerage liquid velocity in the outlet of the opening. v
The opening exit factor is in practice between 0.60 and 0.63 (Feintuch, 1977). If the mean
pressure drop p o at the openings is significantly higher than the pressure drop p across
, utor the distrib the total pressure drop from opening to opening will not vary much, and
consequently, the e v e xit feed rate at each opening will be more or less the same. The relati
variation of feed, expressed as % difference between the first and the last opening M do is
(Perry and Green, 1999)
p
p
M 100 1 o (3.341)
do
p o
The last relation is valid for relatiely small variations of the flow across the distrib . utor
v
The value of M do can be considered equal to 5%, in general. p o can be calculated from
eqs. (3.341) and (3.338), and u the can also be determined from eq. (3.340). Subsequently,
o
total cross-section A o of the openings can be calculated.
Q
A (3.342)
o
u o