Air Oil Coolers
Two basic types of oil coolers in
general use are the air-cooled and the fuel-cooled. Air oil coolers are used in
the lubricating systems of some turbine engines to reduce the temperature of
the oil to a degree suitable for re-circulation through the system. The
air-cooled oil cooler is normally installed at the forward end of the engine.
It is similar in construction and operation to the air-cooled cooler used on
reciprocating engines. An air oil cooler is usually included in a dry-sump oil
system. This cooler may be air-cooled or fuel-cooled and many
engines use both. Dry- sump lubrication systems require coolers for several
reasons. First, air cooling of bearings by using compressor bleed-air is not
sufficient to cool the turbine bearing cavities because of the heat present in
area of the turbine bearings. Second, the large turbofan engines normally
require a greater number of bearings, which means that more heat is transferred
to the oil. Consequently, the oil coolers are the only means of dissipating the
oil heat.
Fuel Oil Coolers
The fuel-cooled oil cooler acts
as a fuel oil heat exchanger in that the fuel cools the hot oil and the oil
heats the fuel for combustion. Fuel flowing to the engine must pass
through the heat exchanger; however, there is a thermostatic valve that
controls the oil flow, and the oil may bypass the cooler if no cooling is
needed. The fuel/oil heat exchanger consists of a series of joined tubes with
an inlet and outlet port. The oil enters the inlet port, moves around the fuel
tubes, and goes out the oil outlet port.
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