particle diameters and fluid viscosities) in a column of L/D=34 (length/diameter) with an
inert bed (glass beads) to which the fluid phase is fed with or without pulsation.
A stimulus-response technique has been used to obtain the Residence Time
Distribution (RTD) of the fluid inside the reactor (Levenspiel, 1988). To do that, a small
volume (one mL) of a tracer (HC1) was injected into the inlet stream of the column in
order to get an almost ideal pulse (δ function of Dirac) and this moment is considered the
beginning of the experiment.
Figure 11.3 shows, as an example, the RTD’s curves obtained in the same operating
conditions (Rep=95, a particle diameter of 6 mm and water as liquid) with an EMP, a
pneumatic pulsator, a self-propelled pulsator and without pulsation. For this set of curves,
the values of the Peclet module are always within the limits of the Minimum Dispersion
model (Levenspiel, 1988). As can be seen, the axial dispersion in the reactor coupled
with the self-propelled pulsator and the EMP are lower than that corresponding to the
system without pulsation. However, the pulsation carried out with the pneumatic
equipment produces greater dispersion, and considerably smaller Peclet modules are
obtained. The lowest degree of dispersion and, consequently, the flow model closest to
the plug flow reactor is achieved by applying the EMP pulsator.
Pulsing bioreactors 335