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

18
clearance ratios as being caused by turbulence. At 0.02
clear~nce ratio there is little or no turbulence. At very
small clearance the high shearing force at the wall increases
the relative heat transfer coefficient.
Baffles
Brooks and Su (30) studied the effects of baffles. Below
a Reynolds n~unber
of 400 the baffles had no effect but
above 400 there was a 37 percent increase in the heat transfer
coefficient. Thi s increas e ,·ras independent of the nu.mber
(one, two or four) of baffles used.
Ackley (1) reports that
using four baffles his data support Brooks and Su.
Ubl
(194) reports that baffles had no effect in the Reynolds
number range of 25 - L~OOO • Chilton (39) reports that removal
of his coil did not seem to effect the heat transfer rate of
the jacket..
Oldshue and Gretton (137) report that Hhen the
baffles were placed 1 inch off the l~all
01'" betHeen the coil
~nd
the impellel'" the heat transfer coefficients al"'e 5 percent
lower th~n
Hhen the baffles are at the Nal1.
Impeller Geometry
Using a coil as the heat transfer surface, CURmings
and vlest (49) found that using t1-JQ
l"'etreating blade turbines
did not increase the heat transfer coefficient but suggested
that this is probably because the fluid height Has equal to
only one vessel diameter.
For a greater fluid height the
second impeller 1 ..vould be expected to increase the coefficient.