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

144
transfer coefficients to non-Nel A ltonian fluids to
As mentioned
in Chapter 2 Blanchard's viscosi t-y ratio shol,rs a misunderst~nding
of the flow in an agitated vessel since he considers
the shear rate at the l,fall to approach infL""li ty 1.[hile in
actuality it~
is 101,f compared to the shear rates near the
impeller (127). The consistency term used by Sal~mone et
al .. (165), (m:gcKS n - l ) is valid for pipe flow (the "8 11 is
introduced du..ring the development of the equations for
fluid flm>! through conduits); hov.rever, the !lSlI does not
have any significance in a stirred vessel. The semiempirical
development in this thesis shows that the factor
11 .. 5 n - l in equation 2-25 has no fundamental basis but it
does successfully correlate the average shear rate with
the impeller speed and thus has empirical significance.
The correlations discussed progressed from a highly
theoretical correlation (Correlation A) to a highly empirical
correlation (Correlation G).
If the two extremes
are compared by the F test on the overall variances Correlation
A is as good as Correlation G for all impellers
except turbines. Correlation A is sig:..n.ificantly better
than Correlation G for turbines. Hm-rever, these results
are biased in favor of the theoretical equation because of
the large amount of Ne'lAJtonian fluid data, for v.Jhich Correlation
A is slightly better..
If each type of fluid for
each impeller is tested, COl"'rela tion G is significantly
better than Correlation A in five of the tv.Jelve non-Newtonian