Sample Chiller0 pages

APPLICATION NOTE
Temperature Control Unit
TCU
A temperature control unit (TCU) provides controlled temperature water (coolant) to a group of sample coolers in order to
ensure closely controlled sample temperatures. These coolers are
usually referred to as secondary coolers.
Typically samples over 100° F (38° C) are precooled in "primary"
sample coolers using plant cooling water. The secondary coolers
are all identical in construction and have a fixed amount of heat
transfer area. The coolers are designed so that the sample leaving
temperature approaches the coolant temperature very closely
(typically less than 0.5°). Therefore, if the temperature of the
coolant on the shell side is constant, and the flow rate of coolant
through each cooler remains constant, sample temperatures will
be very close to the coolant temperature. The heat removed from
the samples is picked up by the coolant and circulated back to the
TCU where the coolant is again reduced in temperature to the
controlled value.
It is possible that one or more samples will come to the secondary
coolers at a temperature below that of the coolant (subcooled).
In those cases the samples will be warmed by the coolant and
approach the coolant temperature from below the set point. If
enough samples are subcooled, the temperature of the coolant
returning to the TCU will be less than the desired control
temperature. In this case, the TCU will add enough heat to bring
the coolant to the controlled value.
The basic TCU is a refrigeration system or chiller. It differs from
the home refrigerator, drinking fountain chiller or air conditioner
in several ways. First, the compressor does not turn on and off
(cycle), but runs continuously. A cycling compressor will bring the
temperature of a circulating fluid (air or water) down to a certain
point, then turn off. When the fluid temperature rises to a set
point, it will turn on again. When water is the circulating fluid,
the temperature spread is typically about 6° F (-14° C). Since a
sample system is typically designed to hold the temperature of all
the samples to +1°, a cycling system is not adequate to do the job.
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Features
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Closed loop pressurized
coolant circulating system
with ODP centrifugal pump.
Water stays clean, no
corrosion or fouling of heat
transfer surfaces.»
PLC controller with display
of all required operational
data.»
No ex tra piping required
other than connecting
to sample system to the
condenser cooling water
sources and to the makeup water source. If a city
potable water supply line is
to be connected for makeup, it is the responsibility of
the installer to check and
abide by all local codes.
APP 5.8.2 Rev. 7 04/12