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

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fluids studied (apparent viscosities behv-een 3000 and 11,000
centipoise) there was little effect of baffles on power
cons~mption, even at Dt/Da as low as 1.67. Dual impellers
required tvdce the pOl-leI' of' a single impeller and this remained
true for various spacings between the impellers.
Quality of Mixing
The quality of mixing is a very important criterllnto
be considered Hhen designing an agitation system, since the
quality or composition of a product is dependent upon the
degree to Hhich reactant or temperature fluctuations are
minimized throughout the vessel. This is especially true
Hi th many processes involving nOn-Nev.Itonian f1uids:l such as
the heating of food products or the polymerization of a
monomer.
l1etzner and Taylor (127) studied the f'lovJ patterns in
an agitated vessel in an attempt to learn more about the
mechanism of' mixing in such a system. They suspended 0.02
"
inch spheres of Plexiglas": in both Ne,itonian and pseudoplastics
fluids and photographed them as the fluid was
being mixed by a disk and vane turbine. The loqal
velocities
were calculated by measuring the streak lengths and dividing
by the exposure time.
A plot of the local velocity versus
radius was differentiated to obtain the local shear rates.
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