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

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tween 0.25 and 0.58. L~~l had reported ~n 18 percent difference
in Nusselt nu..l11bers for an impeller in hw different locations
a..D.d a fev1 authors had mentioned that hi'>.:her heat transf~r
rates Here achieved for certain impeller locations but the
effect had not been studied qua.nti ta ti vely.
The effect of
height variation may have a considerable signific8~ce
since
changes in the impeller height cause minimal if not neglirible
changes in pOHer requirements.
The model proposed in Chapter 3 results in a dLmensionless
equation which acclJ.rately characterizes the batch heat
transfer system as sh01~m by the good fi t achieved. Thus the
model itself may be inferred to be a fairly accurate portrayal
of the :mechanismof heat transfer in an agitated vessel.
To
be more specific~
the center core of tIle fluid is in turbulent
flm! Hi tll. thorough mixing of the fluj e3 in this region. In
addi tion to tlJrbulence in the impeller region, the impel10r
produces bulk fluid .flow, largely axial. This results in
fluid flov~
alon!:. the cylindrical heat tra..Ylsfer surface in
the vertical direction. At the wall surface the flu:td is
motionless.
There is a velocity gradient in the radial
direction. Heat is transferred across the stagnant fluid
layer at the Hall by conduction 8Jld is then transferred by
diffusion and bulk floH into the turbulent core.
TI'le controllinG
factor in the rate of heat transfer is thus a
stagnant layer at the Hall. An increase in the bulk rImA)"
rate through the eye of the impeller (by increasine; im-