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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > Regional Forums > UK > Remember to top up your screenwash



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      01-18-2013, 10:50 AM   #23
F32Dude
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Sooooo... wind whistling through your radiator coils/elements/whatever won't lower the temperature anymore that if your car was stationary?

Isn't that the principle of an intercooler too?

And presumably, to quote the science, the fluid in the washer pipes would be at a higher temp than the surrounding air? So...
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      01-18-2013, 02:21 PM   #24
SteveC
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Thermal dynamics

Quote:
Originally Posted by uke92dude View Post
Sooooo... wind whistling through your radiator coils/elements/whatever won't lower the temperature anymore that if your car was stationary?

Isn't that the principle of an intercooler too?

And presumably, to quote the science, the fluid in the washer pipes would be at a higher temp than the surrounding air? So...


Take a radiator at 80 degrees in stationary air that's at 10 degrees. The radiator/air is in equilibrium and the temperature remains at 80 degrees. Now drive the air through the radiator. The air will be warmed by the radiator, so heat is transferred from the radiator, to the air. The radiator may drop to 60 degrees and the air coming off the radiator may be at 20 degrees.
The higher the airflow, the more heat is removed from the radiator. But no matter how fast the air is moving, it cannot take the radiator to a temperature of less than 10 degrees, unless there is something else going on, like evaporation.

A glass of water will not freeze in 2 degree air, no matter how fast the air is moving

The fluid in the washer pipes may indeed be at a higher temperature than the air, so the air would cool it until the fluid was at the same temperature as the air ie in equilibrium, but not lower, because as soon as the fluid became cooler that the air, the air would transfer heat to the fluid and warm it up.
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      01-18-2013, 02:43 PM   #25
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Quote:
Originally Posted by SteveC View Post
Take a radiator at 80 degrees in stationary air that's at 10 degrees. The radiator/air is in equilibrium and the temperature remains at 80 degrees. Now drive the air through the radiator. The air will be warmed by the radiator, so heat is transferred from the radiator, to the air. The radiator may drop to 60 degrees and the air coming off the radiator may be at 20 degrees.
The higher the airflow, the more heat is removed from the radiator. But no matter how fast the air is moving, it cannot take the radiator to a temperature of less than 10 degrees, unless there is something else going on, like evaporation.

A glass of water will not freeze in 2 degree air, no matter how fast the air is moving

The fluid in the washer pipes may indeed be at a higher temperature than the air, so the air would cool it until the fluid was at the same temperature as the air ie in equilibrium, but not lower, because as soon as the fluid became cooler that the air, the air would transfer heat to the fluid and warm it up.
Thanks for that - laws of thermodynamics and all that. The best explanation is your comment about the glass of water. Now that makes sense and when you think about it, it's bloody obvious!
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