The type III secondary liquid-cooling system also
operates in a similar manner to the type I secondary
liquid-cooling system—the major difference is in the
way that the temperature of the secondary coolant
is regulated. A three-way temperature-regulating
valve is not used, but a two-way temperature-regu-
lating valve is used in the primary cooling loop to
regulate the temperature of the secondary loop.
The duplicate CW/DW heat exchanger is installed
parallel to the first heat exchanger and is used as a
standby heat exchanger. If a malfunction occurs that
requires the first heat exchanger to be removed from
service, the standby exchanger can be put into service
by manipulating the isolation valves associated with
the two heat exchangers.
LIQUID-COOLING SYSTEM
COMPONENTS
The main components of liquid-cooling systems
are heat exchangers, expansion tanks, seawater strain-
ers, temperature-regulating valves, flow regulators,
flow-monitoring devices, circulating pumps, demin-
eralizes, oxygen analyzers, and coolant-alarm switch-
boards. In some systems, there are specialized
components to monitor cooling water to the electronic
equipment.
You should be able to identify and describe the
operation of the individual components of a typical
liquid-cooling system to help you perform the re-
quired system maintenance and trouble isolation. You
should never neglect the cooling system, because it
will quickly deteriorate to a point where only extreme
and costly maintenance will restore it to its proper
performance.
HEAT EXCHANGERS
In liquid-cooling heat exchangers, the heat that
has been absorbed by distilled water flowing through
the electronic components is transferred to the pri-
mary cooling system, which contains either seawater
or chilled water from an air-conditioning plant. In
both cases, the heat exchangers are of the shell and
tube type in which the secondary coolant (DW) flows
through the shell, while the primary coolant (SW or
CW) flows through the tubes.
A single-pass counterflow heat exchanger is more
efficient than the double-pass heat exchanger, because
there is a more-uniform gradient of temperature dif-
ference between the two fluids. The primary coolant
(SW/CW) flows through the tubes in the opposite
direction to the flow of the secondary coolant (DW).
Heat transfer occurs when the seawater flows through
the tubes, extracting heat from the distilled water
flowing through the shell side of the heat exchanger.
The distilled water is then directed by baffles to flow
back and forth across the tubes as it progresses along
the inside of the shell from inlet to outlet. In figure
2-4, the preferred method of double-tube sheet con-
struction is shown. Single-tube sheet construction is
shown in figure 2-5.
2-6
