The transfer of heat from one fluid to another across a solid boundary is of great importance in pharmaceutical processing.
THE TRANSFER OF HEAT BETWEEN
FLUIDS
The
transfer of heat from one fluid to another across a solid boundary is of great
importance in pharmaceutical processing. The system, which frequently varies in
nature from one process to another, can be divided into constituent parts, and each
part is characterized in its resistance to the transfer of heat. The whole
system may be considered in terms of the following equation:
Rate at which heat
is transferred ∝ Total temperature
difference/Total
thermal resistance
A
hot liquid passing through a heavily lagged metal pipe may be con-sidered as an
example. The transfer of heat from the liquid to the pipe, con-duction through
the pipe wall and across the insulation, and heat loss to the surroundings by
natural convection can each be assigned a thermal resistance. A system in which
steam is admitted to the outside of a vertical pipe containing a boiling liquid
may serve as a second example. This arrangement is common in evaporators, and
the evaluation of heat transfer rates demands a study of con-densation,
conduction across the wall of the tube and any deposited scale, and the
mechanism of boiling.
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