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The word radiator is

a hollow metal device for heating rooms. Radiators are usually connected by pipes through which hot water is sent

But it also has the meaning of

a device for cooling the engine of a vehicle or an aircraft

which is the exact opposite.

Etymology says

1836, "any thing that radiates," agent noun in Latin form from radiate. Meaning "heater" is from 1851; sense of "cooling device in internal combustion engine" is 1900.

But I can't see why radiator is used for a cooling device, too. What is the reason?


Interestingly, since 1900 the use of radiator is massively increased:

enter image description here

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Wiktionary: A device that lowers engine coolant temperature by conducting heat to the air, through metal fins. I guess conducting heat is the reason it's called radiator. a device constructed from thin-walled tubes and metal fins, used for cooling circulating water, as in an automobile engine. –  Manoochehr Jun 24 '12 at 15:40
    
@Manoochehr is right on the money: the cooling device works by emitting heat. I would add, though, that even if it emitted frost, chances are it would still be called a radiator simply because of the looks, and because the word radiator doesn't really say anything about what it radiates. If it looks like a radiator and works like a radiator, then it's a radiator. –  RegDwigнt Jun 24 '12 at 15:57
    
How did you make this awesome graph? –  Michael Jun 24 '12 at 16:39
1  
@Michael: It is a Google nGram. –  user19148 Jun 24 '12 at 16:51
    
Unsurprisingly, many related words have similar increased usage since 1900. –  J.R. Jun 24 '12 at 18:24
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1 Answer

up vote 22 down vote accepted

They work in exactly the same way - take heat from the circulating water, and radiate it.

The only difference is that in one case you want the heat in the room, and in the other you want to dissipate it to the surrounding air.

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In the second case you're still heating a room: the big blue room. –  dmckee Jun 25 '12 at 2:18
    
And ironically in both case the heat transfer is almost all convective not radiative –  mgb Jun 25 '12 at 3:01
    
Funny how an English question has a Physics answer –  Lourens Jun 25 '12 at 6:55
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