January 07, 2015
Cooling system
Cooling system Written by: The Editors of Encyclop?dia Britannica Cooling
system, apparatus employed to keep the temperature of a structure or device from
exceeding limits imposed by needs of safety and efficiency. If overheated, the
oil in a mechanical transmission loses its lubricating capacity, while the fluid
in a hydraulic coupling or converter leaks under the pressure created. In an
electric motor, overheating causes deterioration of the insulation. The pistons
in an overheated internal-combustion engine may seize (stick) in the cylinders.
Cooling systems are employed in automobiles autel
ds708, industrial plant machinery, nuclear reactors, and many other types of
machinery. (For a treatment of cooling systems used in buildings, see
air-conditioning.) The cooling agents customarily employed are air and a liquid
(usually water or a solution of water and antifreeze), either alone or in
combination. In some cases, direct contact with ambient air (free convection)
may be sufficient; in other cases, it may be necessary to employ forced-air
convection, created either by a fan or by the natural motion of the hot body.
Liquid is typically moved through a continuous loop in the cooling system by a
pump. In a transmission, if the surface area of the housing (container) is
sufficiently large compared with the power lost, or if the transmission is in a
moving vehicle, there is usually adequate free convection and no need for
artificial cooling. To augment the cooling effect by increasing the surface
area, the housing may be provided with thin metal fins. On some stationary
mechanical transmissions, it may be necessary to circulate the lubricating oil
through pipes surrounded by cold water or to use a fan to blow air through pipes
surrounded by the oil in the reservoir. On many electric motors, a fan is
attached to the rotating element to create a current of cooling air through the
housing. In an automobile, the motion of the vehicle provides sufficient
forced-convection cooling for the transmission and the gears in the rear axle;
in the engine, however, so much energy is released that, except for some early
models and certain small cars with low-powered engines autel
maxidas ds708, air cooling is inadequate, and a water cooling system
(radiator) is required. 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 liquid to carry away heat; (2) a radiator,
consisting of many small tubes equipped with a honeycomb of fins to convect heat
rapidly, that receives and cools hot liquid from the engine; (3) a water pump,
usually of the centrifugal type, to circulate the liquid through the system; (4)
a thermostat to control temperature by varying the amount of liquid going to the
radiator; and (5) a fan to draw fresh air through the radiator. To prevent
freezing, an antifreeze solution is either added to or substituted for water. To
raise the boiling point of the solution, the cooling system is usually
pressurized by means of a pressure cap on the radiator with valves that open
outwardly at a prescribed pressure and inwardly to prevent a vacuum as the
system cools.
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