Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plants or any similar use of such an engine.
Internal combustion engines are often cooled by circulating a liquid called engine coolant through the engine block, and cylinder head where it is heated, then through a radiator where it loses heat to the atmosphere, and then returned to the engine. Engine coolant is usually water-based, but may also be oil. It is common to employ a water pump to force the engine coolant to circulate, and also for an axial fan[1] to force air through the radiator.
Automobiles and motorcycles[edit]Coolant being poured into the radiator of an automobile
In automobiles and motorcycles with a liquid-cooled internal combustion engine, a radiator is connected to channels running through the engine and cylinder head, through which a liquid (coolant) is pumped by a coolant pump. This liquid may be water (in climates where water is unlikely to freeze), but is more commonly a mixture of water and antifreeze in proportions appropriate to the climate. Antifreeze itself is usually ethylene glycol or propylene glycol (with a
small amount of corrosion inhibitor).
A typical automotive cooling system comprises:
· a series of galleries cast into the engine block and cylinder head, surrounding the combustion chambers with circulating liquid to carry away heat;
· a radiator, consisting of many small tubes equipped with a honeycomb of fins to dissipate heat rapidly, that receives and cools hot liquid from the engine;
· a water pump, usually of the centrifugal type, to circulate the coolant through the system;
· a thermostat to control temperature by varying the amount of coolant going to the radiator;
· a fan to draw cool air through the radiator.
The combustion process produces a large amount of heat. If heat were allowed to increase unchecked, detonation would occur, and components outside the engine would fail due to excessive temperature. To combat this effect, coolant is circulated through the engine where it absorbs heat. Once the coolant absorbs
the heat from the engine it continues its flow to the radiator. The radiator transfers heat from the coolant to the passing air.
Radiators are also used to cool automatic transmission fluids, air conditioner refrigerant, intake air, and sometimes to cool motor oil or power steering fluid. A radiator is typically mounted in a position where it receives airflow from the forward movement of the vehicle, such as behind a front grill. Where engines are mid- or rear-mounted, it is common to mount the radiator behind a front grill to achieve sufficient airflow, even though this requires long coolant pipes. Alternatively, the radiator may draw air from the flow over the top of the vehicle or from a side-mounted grill. For long vehicles, such as buses, side airflow is most common for engine and transmission cooling and top airflow most common for air conditioner cooling.Radiator construction[edit]Automobile radiators are constructed of a pair of metal or plastic header tanks, linked by a core with many narrow passageways, giving a high surface area relative to volume. This core is usually made of stacked layers of metal sheet, pressed to form channels and soldered or brazed together. For many years radiators were made from brass or copper cores soldered to brass headers. Modern radiators have aluminum cores, and often save money and weight by using plastic headers with gaskets. This construction is more prone to failure and less easily repaired than traditional materials.
An earlier construction method was the honeycomb radiator. Round tubes were swaged into hexagons at their ends, then stacked together and soldered. As they only touched at their ends, this formed what became in effect a solid water tank with many air tubes through it.[2]
Some vintage cars use radiator cores made from coiled tube, a less efficient but simpler construction.