Apparatus used to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency.
In a mechanical transmission, the oil loses its lubricating capacity if overheated; in a hydraulic coupling or converter, the fluid leaks under the pressure created. In an electric motor, overheating causes deterioration of the insulation. In an overheated internal-combustion engine, the pistons may seize in the cylinders. The cooling agents customarily employed are air and a liquid (usually water), either alone or in combination. In some cases, direct contact with ambient air (free convection) may be sufficient, as in cooling towers; in other cases, it may be necessary to employ forced convection, created either by a fan or by the natural motion of the hot body. Cooling systems are used in automobiles, industrial plant machinery, nuclear reactors, and many other types of machinery. See also air conditioning , heat exchanger .