Prediction of batch heat transfer coefficients for pseudoplastic fluids ...

24
~or
determining the apparent viscosity, it is rather time
consuming and expensive, since it requires much experimental
work.
Metzner and Otto (~ used a similar approach, but
generalized it so that prediction o~
the apparent viscosity
can be made directly from the rheological data ~or
any time
independent fluid. They noted that an agitator in a vessel
is some1tJhat analogous to the rotating bob of a viscometer.
For a viscometer bob rotating in an i~inite
fluid the
shear rate is proportional to the bob's rotational speed.
(2-19
They reasoned that the shear rate at the agitator of a mixing
vessel might also be represented by this equation.
If
this CAJere true and Ks 'i-Jere evaluated the apparent viscosity
could be determined from the rheological data plotted as
apparent viscosity versus shear rate.
Metzner and Otto tested this idea by first determing
the NevJtonian Pm-Ier mnnber-Reynolds number curve for many
different system geometries.
They then evaluated the
rheological properties of five non-Nev-Ttonian fluids and
plotted the apparent viscosity versus the shear rate. These
~luids Here then mixed and the pO'L..rer data taken. The apparent
viscosities \Alere calculated by the method o~
I'lagnussen (1J2)
and the shear rates determined from the rheological curves.