
220 Green Chemical Engineering
uid. Whereas in an ideal PFR, the tracer material, while it is being carried along by the
bulk uid moving at velocity ū, does not spread in the axial direction. In a PFR with axial
mixing characteristics, the gradual spreading (dispersion) of the tracer material in the axial
direction after a time lapse of θ
1
, θ
2
and θ
3
(θ
3
> θ
2
> θ
1
) from the time of injection of tracer is
depicted in Figure 3.60. The dispersion ux of the tracer material J (kmol/m
2
s) is written as
=−
(3.320)
where dC/dz is the tracer concentration gradient and D is the dispersion coefcient
expressed in the unit m
2
/s. D = 0 for an ideal ...