Page 269 - gas transport in porous media

Šolcová and Schneider
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time. Of course, simultaneous determination of three mutually correlated parameters
leads to deterioration of their confidence. Hence, evaluation of transport parameters
from processes of this kind is recommended rather as a check for consistency of
parameters from separate diffusion and permeation processes.

14.6.1 Dynamic Wicke-Kallenbach Cell

Combined diffusion and permeation under dynamic conditions can be followed in
the adapted Wicke-Kallenbach diffusion cell (Figure 14.15) (Arnošt and Schneider,
1995). The same carrier gas, C, flows steadily through both chambers of the cell with
L
volumes, V U and V . The flow of carrier gas in the upper cell is either substituted
by a flow of tracer gas, T, or perturbed by and impulse of the tracer gas, T. Tracer
concentration is monitored at the outlet of the lower chamber. This response can be
compared with theoretical predictions based on MTPM and DGM. The governing
mass balance has the form

∂c(x, t) ∂ −1 ∂c(x, t)
ε = F (c(x, t)) (14.50)
∂t ∂x ∂x

Tracer input
a b

t t
6 7

1
3 4
2

6 5
Tracer output
a b

t t
Figure 14.15. Dynamic version of the Wicke-Kallenbach diffusion cell. 1 upper cell compartment, 2
lower cell compartment, 3 cylindrical porous pellets, 4 impermeable pellet holder, 5 tracer detector,
6 carrier gas inlet, 7 carrier gas/tracer-gas switch, a carrier/tracer step change, b tracer impulse