exchanger. This type of heat exchanger is less ef-
ficient than a single-pass exchanger and is subject to
internal undetectable leakage across the flow divider
in the inlet-outlet water box.
Heat exchangers must periodically be cleaned.
The secondary section (distilled water) is cleaned by
circulating chemicals through the secondary cooling
system to remove any buildup of scale deposits that
may accumulate on the surface of the tubes.
The procedure for routine cleaning of the primary
section of the heat exchanger is to first secure the sea
connections to prevent flooding. In some cases, an
inspection port in the water box can be opened to
remove any foreign matter lodged inside and against
the tubes. If you are unable to get at the ends of the
heat exchanger to remove the water boxes, then you
must remove the heat exchanger from its location and
place it on the deck or on a suitable work surface.
Mark each unit removed so that it can be positioned in
its proper place during reassembly. With the water
boxes removed, an air lance should be passed through
each tube and the passages washed out. Where severe
fouling exists, a water lance should be pushed through
each tube to remove foreign matter attached to the
tube walls.
Where extreme fouling exists, special cleaning
equipment operated by personnel skilled in its use is
required. The ship’s engineering officer is normally
the best person qualified to determine which proce-
dure to use and whether the job can be performed
aboard ship or if it must be transferred to a repair
facility. You should take precautions to ensure that
tools, such as screwdrivers and wire brushes, are not
used in such a way that they may scratch or mar the
tube surfaces.
Over a period of time, electrolysis, which results
because of dissimilar metals in the cooling system,
will slowly dissolve the insides of various compo-
nents in the primary seawater cooling system. Elec-
trolysis is not a problem in chilled-water systems to
the extent that it is in seawater systems. The type of
metal used in the fabrication of the heat exchanger
tubes is the deciding factor as to the use of zincs.
Zincs are disks, rods, bars, or plates made of zinc
metal that are installed inside the heat exchanger’s
water boxes. When they are installed, the electrolytic
action is concentrated on the zinc and not on the metal
of the heat exchanger tubes. As electrolysis dissolves
the zincs instead of the heat exchanger tubes, they
should be replaced. (The purity of distilled water
inhibits electrolysis in the secondary system.)
In an older cooling system, you should be on the
lookout for thin pipes in the seawater side of the
cooling system. Check for bad pipes by gently tapping
the empty pipes with the ball end of a ball-peen
hammer. A bad piece of pipe will make a dull sound
and will dimple as it is struck lightly.
The heat exchangers in the distilled-watercooling
systems that cool electronic equipment are either
liquid-to-air or coolant-jacket type of heat exchangers.
The liquid-to-air heat exchangers are mounted inside
cabinets containing the heat-producing electronic
components.
A cabinet fan circulates the air across the heat
exchanger and to the heat source in an airtight circuit.
In the coolant-jacket type of heat exchangers, the
distilled water is circulated through an integral water
jacket in a large heat-producing component, such as a
power-amplifier tube, a plate transformer, or the load
isolators.
Vent and drain connections are provided to permit
venting trapped air and draining water. Temperature
gages may be provided in the inlet and outlet piping
to check performance of the heat exchanger. Label
plates indicate the water-flow direction through each
cabinet.
Flow regulators (orifice plates or constant-flow
devices) usually provide a constant flow of coolant to
the individual component, cabinet, or bay of elec-
tronic equipment to be cooled. On critical electronic
components that would be damaged without coolant
to remove the heat, coolant-flow and temperature
switches monitor the coolant.
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