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

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for viscous pseudoplas tics at 101'1 values of' Dt/Da • A fan
turbine seems to be better than both one or hw disk and
vane turbines except at high values of Dt/D a . The a..'dal
flmAj" component must aid in mixing normally stagnant regions.
At high Reynolds n~mbers the fan turbine loses its advantage.
Table 2-1 lists the minimum Reynolds nlli'l1ber required
for movement near the wall for pseudoplastic fluids.
Mixing is best accomplished in the turbulent regions.
For pseudoplastic fluids this region is usually confined to
the center of the vessel. Thus to improve mixing efficiency
low values of the tffiL~ diameter to impeller diameter ratio
should be used and/or multiple impellers. Dilatant fluids
are not sensitive to lowering Dt/Da or usli~g multiple impellers
(122).
Lee, Finch and Wooledge (104) injected dye one inch
above the impeller ru~d noted the time needed for complete
mixing. Godleski and Smith (75) added a saturated solution
of phenolphthalein to the fluid and then acid Has added. A
short time later base was added and the time required for
the indicator to change color was measured. Both groups
report that the mixing time in baffled vessels vJaS longer
than in unbaffled vessels. Godleski and Smith report that
the mixing time (in seconds) is related to the voy'tex depth,
H v ' and the impeller dia.me-ter by