# The Naked Scientists Forum

### Author Topic: How does a radiator affect propulsive force?  (Read 1062 times)

#### Geezer

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##### How does a radiator affect propulsive force?
« on: 24/12/2011 06:04:56 »
Internal combustion engines produce a lot of waste heat, and a fair amount of that ends up being dissipated from the cooling system via the "radiator". When the vehicle is not moving, a fan moves air through the radiator to conduct heat into the moving air. Obviously, the fan consumes power when it is running, but when the vehicle is moving the fan is (typically) freewheeling as the motion of the vehicle is sufficient to move enough air through the radiator elements to remove the waste heat.

Does the vehicle have to produce the same amount of power to push air through the radiator whether or not the vehicle is moving, or is there some "free energy" available because the vehicle is moving?

(I was going to post this in Technology, but I suspect it's more to do with conservation of energy, so I stuck it here.)

#### syhprum

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##### Re: How does a radiator affect propulsive force?
« Reply #1 on: 24/12/2011 06:37:27 »
There is certainly free power available from the the air passing thru the "radiators" on propellar driven aircraft a net thrust is produced.
On road vehicles due to the position of the "radiators" and the lower speeds this is not normally available

#### MikeS

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##### Re: How does a radiator affect propulsive force?
« Reply #2 on: 24/12/2011 07:44:20 »
I imagine you could regard it as free (as the vehicle is already moving).  However, it would still require the same amount of energy to move air through the radiator regardless of whether the vehicle is moving or via the fan.  Either way that energy  one way or another comes from the engine (so you have to pay for it).
« Last Edit: 27/12/2011 11:24:06 by MikeS »

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##### Re: How does a radiator affect propulsive force?
« Reply #2 on: 24/12/2011 07:44:20 »