Page 121 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

116

(11)
Bo, Bo 2

The Peclet number Pe L is determinant from the Bodenstein number Bo L
by the equation:

Pe -
aH

2
3
where a is packing specific surface area, m /m . Pei, and also Peelet number for
the gas phase is a characteristic of the type and dimension of the packing, and of
its hydrodynamics, and is independent of its height. That is why it is used in the
dimensionless equations for calculation of the axial mixing coefficient. Because
the mathematical model use Ba L, and also Bo G, the latter can be obtained from
the dimensionless equations for Pe using equation (12).
The dispersion of the tracer retention time O" can be determined using
the equation:

- \C(t)dt

, (13)
)TC(T)

where C(r) is the concentration of the tracer after the packing as a function of
the timer, measured from the moment of feeding the tracer in the form of
a S function. At very low concentrations it is proportional to the electric
conductivity of the solution. It is easy to see from Eq. (13) that if the
conductivity instead of the concentration is put, the coefficient of
proportionality can be eliminated by cancellation. That gives the possibility
under this condition to use the conductivity of the liquid phase, instead of the
concentration C.
The integrals in Eq. (13) can be obtained using either analog or digital
computer operating online with the experimental installation. The analog
devices give good results when the integration time is less than 100 s.