generated by the pulsing system. As the solutions exhibit a Newtonian behaviour
(viscosity only depending on the temperature), the effects of pulsation can be determined
at different flowrates. The increase in DA at higher linear velocity is remarkable even in
the cases of high viscosity fluids, the axial dispersion coefficients being, on average,
approximately twice as high as those obtained with water (Figure 11.4).
Figure 11.4 Effect of linear velocity
on axial dispersion for a packing of 6
mm of particle diameter using two
fluids of different viscosities (water
and a sucrose solution of a viscosity of
2 cP).
Finally, the effects of the packing size were analysed by evaluated columns with particles
of three different diameters (4.5, 6 and 8 mm). In all cases, DA decreases with the particle
diameter, this tendency being noticeable when operating at higher feed flowrates (data
not shown).
APPLICATION OF PULSING BIOREACTORS TO
BIOTECHNOLOGICAL PROCESSES
The development of high efficiency bioreactors has been an important research objective
in the field of bioprocesses. Appropriate selection and design could greatly improve the
efficiency of the overall process. Several bioreactor configurations (fixed/fluidised-bed,
gas-lift, membrane fermentors, reciprocating bioreactors) have been considered (Brauer,
1988; Chamy et al., 1990; Chisti, 1989; Mehaia and Cheryan, 1984). In many cases, gas-
Pulsing bioreactors 337