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

20
l'UXIlfG OF NON -NE1rJTONIAN FLUIDS
The mixing of non-Newtonian fluids in an agitated
vessel is a 'lIDi t operation somel'1fhat similar to batch heat
transfer. It is presented because some of the results of
the Hork on mixing can be utilized in developing a correlation
for predicting batch heat transfer coefficients.
Batch heat transfer could be classified as a problem involving
the quality of mixing but it is usually considered
as a separate study.
A review of the small amount of Hork
on batch heat transfer to non-Nel'ITtonian fluids will be
considered later in this chapter.
This section reviel'JS
the study of pov-rer requirements and the quality of mixing.
Much of the work on fluid flow and heat transfer to pseudoplastics
in pipes (revie'tved in \1Iilkinson.1 213; Metzner, 118;
and Thomas, 190) was theoretical in nature. The geometry
and flO1..J patterns in an agitated vessel, hmvever, are rather
complex for this approach.
The velocity profile in a pipe
could be quantitized since it was only a function of wall
shear stress, average velocity, and rheological parameters.
In addition the flow Has in only one direction.
In a mixing
vessel the floH is three dimensional, the "\-lall shear stress
is QnY~OHn,
and the average velocity is not only difficult
to define, but is dependent upon the rheological properties,
the speed of the agitator, the shape, dimensions, and position
of the agitator, and the vessel geometry..
Because of great
number of 'lIDknown relationships, which are made even more