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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
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