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

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2: a in in heat cQ@tent of the vessel.
A second method of calculating the qtta....'1ti ty of heat
transferI'ed is to calculate the change in enthalpy of the
batch.
There are three corrections 1lrhich must be taken
into account ..
1. The heat losses from the sUT'face of the
fluid.
2. The mechanical energy input from the ar;itator.
3. The gain in heat content of the impeller and
shaft.
There is usually at least 20 percent vapor space during a
heat transfer experiment and the vessel is covered Hith an
insulated lid. If the temperature of the batch does not
approach the boilinl; point the heat losses from the surface
are negligible. The mechanical energy input to the system can
be calculated if DOHer measurements are made (they llsually
are). ROHever, the mechanical energy input is significant
only if very viscous fluids are being aGitated.
The gain
in heat content of the impeller 8illd shaft is also neglicible
because of their small ilJeic;ht and heat capacity in
comparison v'Ii th that of the batch fluid.
The temperature
change of the batch can be chosen large enough so that
errors in measurinrz it are small.
It is this author's
opinion that this second method is the most accurate means
of determining the heat transfer rate.