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

23
the Nusselt namber predicted using Correlation D ~or
the
propeller data.
The line vIi th slope equal to unity represents
a per~ect
fit of the data. As can be seen the more pseudoplastic
fluids seem to be represented by lines with a greater
slope.
Similar plots for the other impellers shm-l the same
trend. The dimensional analysis of Chapter 3 suggests using
a variable exponent for the Reynolds number and an additional
par8JJ1eter, n.
Correlation D Has thus modified to give
Correlation E ..
NNU" CNR€ %,,' NpJt h{::r(g:r(~:run F (5-7
1ne constants and average errors are presented in Table 5-9.
The measured Nusselt TI1. .. lluber for the propeller data versus
the predicted Nusselt number is plotted in Figure 5-5. Comparison
o~
Table 5-8 and 5-9 and Figures 5-4 and 5-5, shows
that correlation E fits the experimental data better than correlation
D 1"i th the pseudoplastic fluids gaining the most
improvement ..
Treating each ~luid
separately sho"t-led exponent of the
viscosity correction varied with 1/nO.75 . This modification
was incorporated into correlation F:
A I = eN I
0./1(1{ A
I 6 ( j( )C/ n o.75( D2-)d(ZlIa...)€
IV IVV' Re IVp..h KrP Da DC(..m (5-8
The consta.nts and average errors are presented in Table
5-10.. Comparison of the average errors shmoJs that correlation
F is a might improvement over correlation E.
f