Page 189 - Adsorption Technology & Design, Elsevier (1998)

Design procedures 175

Re = dog (6.63)
P
where dp is the particle diameter, G is the mass flux, and p is the fluid
viscosity.
A dimensionless friction factor, f, is defined by:

AP f G z
= (6.64)
L 2dpp
where AP is the pressure drop, L is the bed length, and p is the fluid density.
Equation (6.65) is used to calculate ffor the Ergun (1952) correlation:

f= 3.5 + 300 ~e (6.65)

The particle diameter d o is defined to be the equivalent diameter of a sphere
having the same specific surface area (i.e. particle area/particle volume) as
the particle. It is important also to note that the coefficients 3.5 and 300 in
equation (6.65) were obtained by Ergun for specific packings. Thus the
equation may not be strictly valid for the majority of adsorption columns in
which the adsorbent is expected to be in granular or pelleted forms. In order
to overcome this limitation, Handley and Heggs (1968) provide further data
on the coefficients and on a method which can be adopted for determining
the appropriate coefficients for any particular fluid-adsorbent combination.
In the Leva correlation (1949) the friction factor fis derived from another
factor f' which is a function only of Re and a shape factor ~,~:
(
f' 1-e) 3-n
f = ~3s_ne 3 (6.66)
In the Leva correlation the particle diameter is the equivalent diameter of a
sphere having the same volume as the particle. The value of the coefficient n
increases from 1 to 2 as flow is changed from the laminar to the turbulent
regimes. In order to take into account the effect of flowrate on pressure
drop, Chilton and Colburn (1931) provide two correlations for the friction
factor, depending on the value of Re:

f= _ 805 for Re < 40 (6.67)
Re
38
f= Re0.t 5 for Re > 40 (6.68)

The Darcy equation should be used if the flow through a packed bed is