Editing Radiator (section)

==Engine cooling==
[[File:Radiateur de voiture - 2.jpg|thumb|right|Car engine bay, with radiator in front]]
{{Main|Radiator (engine cooling)}}
[[File:Radiatore.jpg|thumb|Auto radiators with double grids of tubes: staggered grids on the left, parallel grids on the right]]
Radiators are used for cooling [[internal combustion engine]]s, mainly in automobiles but also in [[Piston engine|piston-engined]] aircraft, [[railway locomotive]]s, [[motorcycle]]s, [[Fossil-fuel power plant|stationary generating plant]]s and other places where [[heat engines]] are used ([[watercraft]]s, having an unlimited supply of a relatively cool water outside, usually use the liquid-liquid [[heat exchanger]]s instead).

To cool down the heat engine, a [[coolant]] is passed through the [[engine block]], where it absorbs heat from the engine. The hot coolant is then fed into the inlet tank of the radiator (located either on the top of the radiator, or along one side), from which it is distributed across the radiator core through tubes to another tank on the opposite end of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers much of its heat to the tubes which, in turn, transfer the heat to the [[Fin (extended surface)|fins]] that are lodged between each row of tubes. The fins then release the heat to the ambient air. Fins are used to greatly increase the contact surface of the tubes to the air, thus increasing the exchange efficiency. The cooled liquid is fed back to the engine, and the cycle repeats.  Normally, the radiator does not reduce the temperature of the coolant back to ambient air temperature, but it is still sufficiently cooled to keep the engine from overheating.

This coolant is usually water-based, with the addition of [[glycol]]s to prevent freezing and other additives to limit [[corrosion]], [[erosion]] and [[cavitation]]. However, the coolant may also be an oil. The first engines used [[thermosiphon]]s to circulate the coolant; today, however, all but the smallest engines use [[pump]]s.<ref>{{Cite journal |last=Diamant |first=N S |title=Engine-Cooling Systems and Radiator Characteristics |date=1924 |url=https://www.jstor.org/stable/44723708 |journal=SAE Transactions |volume=19 |pages=295–336 |jstor=44723708 |issn=0096-736X}}</ref>

Up to the 1980s, radiator cores were often made of [[copper]] (for fins) and [[brass]] (for tubes, headers, and side-plates, while tanks could also be made of [[brass]] or of [[plastic]], often a [[polyamide]]). Starting in the 1970s, use of [[aluminium]] increased, eventually taking over the vast majority of vehicular radiator applications. The main inducements for aluminium are reduced weight and cost.{{citation needed|date=May 2020}}

Since air has a lower [[heat capacity]] and [[density]] than liquid coolants, a fairly large [[volume flow rate]] (relative to the coolant's) must be blown through the radiator core to capture the heat from the coolant. Radiators often have one or more [[Mechanical fan|fan]]s that blow air through the radiator. To save fan power consumption in vehicles, radiators are often behind the grille at the front end of a vehicle. [[Short ram air intake|Ram air]] can give a portion or all of the necessary cooling air flow when the coolant temperature remains below the system's designed maximum temperature, and the fan remains disengaged.{{citation needed|date=May 2020}}