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How cooling system work |
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Liquid cooling systems are employed by most engines
today. A typical automotive cooling system comprises
(1) a series of channels cast into the engine block and cylinder head,
surrounding the combustion chambers with circulating water or other coolant to
carry away excessive heat,
(2) a radiator, consisting of many small tubes equipped with a honeycomb of
fins to radiate heat rapidly, that receives and cools hot liquid from the
engine,
(3) a centrifugal-type water pump with which to circulate coolant,
(4) a thermostat, which maintains constant temperature by automatically varying
the amount of coolant passing into the radiator, and
(5) a fan, which draws fresh air through the radiator.
For operation at temperatures below 32º F (0º C), it is necessary to prevent
the coolant from freezing. This is usually done by adding some compound to
depress the freezing point of the coolant. Alcohol formerly was commonly used,
but it has a relatively low boiling point and evaporates quite easily, making
it less desirable than organic compounds with a high boiling point, such as
ethylene glycol. By varying the amount of additive, it is possible to protect
against freezing of the coolant down to any minimum temperature normally
encountered. Coolants contain corrosion inhibitors designed to make it
necessary to drain and refill the cooling system only once a year.
Air-cooled cylinders operate at higher, more efficient temperatures, and air
cooling offers the important advantage of eliminating not only freezing and
boiling of the coolant at temperature extremes but also corrosion damage to the
cooling system. Control of engine temperature is more difficult, however, and
high-temperature-resistant ceramic parts are required when design operating
temperatures are significantly increased.
Pressurized cooling systems with operating pressures up to 14 pounds per square
inch (100 kilopascals) have been used to increase effective operating
temperatures. Partially sealed systems using coolant reservoirs for coolant
expansion if the engine overheats were introduced in 1970. |
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