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                  3.8 T Fluid–Solid Fluidized Bed Reactors w o-Phase,  213


                  For Group B powders  (Type B fluidization)

                                            0.54        0.4    0.5 0.8
                                       d         u (  u    z ) (  N 4   )           (3.507)
                                        bub   0.2  s  fm
                                             g
                  and

                                              u  bub       bub  gd(  )  0.5         (3.508)
                                                   bub

                  where:
                          d  bub    the equiolume diameter of the b alent v v ubble
                          z     the height aboe the fluid distributor (bed bottom) v
                          N     the number of holes per unit area in the distrib 1/m utor ,  2
                            bub    a constant dependent on the bed diameter   D :

                                              0.64   for  0.1 m D
                                             
                                          bub     1.6   D  0.4  for 0.1  1 m
                                                            D
                                             
                                              1.6  for  1 m D

                  To calculate an aerage value of the bubble v an aerage bubble diameter should v
                   ,
                  v
                   elocity
                  also be used, which can be taken to be equal to the bubble diameter at   Z   H  f  /2. An iter-
                  ation method should be used (Figure 3.60). As an initial   Z  f  value, the fed-bed height  ix  Z
                  multiplied by 1.4 could be used.
                  For Group A powders (Type A bubbling fluidization)
                  For this kind of particles, bubbles reach a maximum stable size, which may be estimated
                  wing equations: from the follo

                                                       u  2 ter,2.7
                                                d    2                              (3.509)
                                                 bub
                                                         g

                                              u       gd(  )  0.5                   (3.510)
                                               bub  bub  bub
                  where:
                                              1     for  D  0.1 m
                                             
                                         bub     2.5   D  0.4  for 0.1  1 m
                                                            D
                                             
                                              2.5  for  1 m D

                  and   u  ter  ,2.7  is the terminal free-fall velocity for particles of diameter 2.7 times the actual
                  mean particle diameter. In all equations, SI units should be used.
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