The apparent shear rate in foaming condition needs to be evaluated
as it is a strategic parameter for mixing and gas bubbles
breakup. However, its determination from Eq. (8) is only valid in
creeping flow. The dimensional range of process shear rate is presented
in Fig. 5 as a function of Reynolds numbers for the two SMX,
as far as the Reynolds number value indicates the reliability of the
shear rate model in the range of operating conditions. The curves
are plotted for two fluids of different properties, one is a monophasic
oil (glycerol solution 25 wt%), and the other is a typical foam of
0.8 void fraction, by considering the density, qf, as (1 a) ql and
the velocity, Us, is the sum of liquid Ul and gas Ug velocities. The viscosity
used in the Reynolds number is of the order of magnitude
taken from our experiments, about 0.1 Pa s nearly constant for
the whole flow rates range. This diagram shows that even with
the highest flow-rates (gas and liquid) encountered in this study,
the flow is laminar, which justifies the use of the process viscosity
calculation.