Page 54 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

49

/ = J- (0 <0 ) and f = 0 (0 >0 ), (157)
T
O
O
t
From (156) and (157) it follows:

(158)

1.5.2.2.3, Model of Danckwerts
The model of Higbie [18] accepts that the exposure for all liquid
particles at the interface is the same. It is clear, that such an acceptation is too
rough to be true.
Danckwerts [19] defines/by the equation:

(159)

1
where s in s" is the rate of renewal of the interface, i.e. the part of the surface
renovation per unit of time which is constant, independent of the age of the
surface. From Eq. (156) and (159) it can be obtained:

k L=4Ds. (160)

Because of very small difference between the results obtained after the models
of Higbie [18] and Danckwerts [19], it is offered [20 p.20] for both of them to
use equivalent diffusion time 0 D calculated by the equation:

k,=— (161)
0