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

neglecting the heat capaci ty of the 1"all, mus t be transferred
th..rough the wall..
Thus the value of ATs-0/ki.l
must equal Ll.Ts_Yl/h. hm and L/lrw are constant over the
H"hole heat transfer surface and the overall driving force,
~To' is also constant.. Thus h is greater in a well
agitated portion than in a poorly-agitated portion the total
resistance to heat flov! in the former portion l-Jill be less
than in the latter, giving rise to a greater heat flQX in
the well-agitated region.
Since the heat flux is higher in the v.iell-agi tated
regions, the ratio,6Ts-IL/ktl' in that region must be
greater than in the poo:r'ly-agi tated l"egions.
Thus the
driving force across the 1Ajall in the v-rell-agi tated regions
is Greater than in the poorly -agi tated regions..
This phenomena
(Nas manifested by the Hall s1..u"face being closer to the
batch temperature in the \.Jell-agi tated regions.
Experimentally it was found that by proper location of
the impeller the differences in wall temperature could be
virtually eliminated, even at 10VI impeller speeds.
These
positions, surmnarized in Table 5-1, probably gave more
uniform agitation.
It is interesting to note that the Optinlum
posi tion for the paddles and turbines is at the level vJhere
about one half of the heat transfer surface is above and one
half beloH the impeller.
The propeller, v-d th its large axial
flow component had to be positioned somewhat higher. These