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

49
A pitched blade turbine gave coefficients about ten percent
lower than the retreating blade turbine and reversing the
flow direction of the pitched blade turbine did not increase
the heat transfer rate..
Oldshue and Gretton (J.l7)using a
coil, report that a rotating impeller causes two phenomena:
a. Turbulence in the region of the impeller and
its wake.
b. Bulk fluid flm..r ..
Both these phenomena are needed for good heat transfer, but
bulk fluid flow is probably more important.
An increase in
the impeller diameter to vessel diameter ratio at constant
Reynolds number, should increase the bulk flow component at
the expense of the turbulence component.
Thus the heat transfer
coefficient should increase Hith increasing diameter
ratio. They report
lJhich is in accordance ljd th their theory.
Pursell (150) and
Ruckenstein (160) using jackets, and thus the vessel wall as
the heat transfer surface,. report that the heat transfer coefficient
decreases \-lith increasing eliameter ratio..
data indicate
Their
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a, t
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