Re: Colors under the hood (air box busted)

["Martin Pajak" <quattro@rogerswave.ca>]

> The light under the hood is infrared (= heat radiation)... the "color"
> of the object is more meaningful when this is considered, ie does it
> absorb or reflect IR?

Just becouse there is no visible light does not mean there is no 
radiation going on.  Specrum runs all the way from Gamma rays to 
microwaves.

1. A blackbody absorbs all incident radiation, regardless of 
wavelength and direction.
2. For a prescribed temperature and wavelength, no surface can emit 
more energy than a blackbody.
3. Although the radiation emitted by a blackbody is a function of 
wavelength and temperature, it is independent of direction.  That is, 
the blackbody is a diffuse emitter.

Emissivity (Ratio of the radiation emitted by a surface to the 
radiation emitted by a blackbody at the same temperature) is 
dependent on the wavelength and the objects temperature.
For example at 300K Solar emissivity of human skin is the same as a 
black painted metallic surface (0.97). When comparing emissivity of 
stainless steel @ 1000K the highly oxidized has a value of 0.67 
compared to 0.23 for highly polished.  So the surface finish has a 
great impact on it as well.  My book does not list different paints 
at high temperatures if someone has access and can compare emissivity 
for different colors it would probably show that flat black surfaces 
have the best emissivity.
Refrences:" Introduction to Heat Transfer" Third Edition by Frank P. 
Incropera and David P. DeWitt 
HTH.




Martin Pajak
quattro@rogerswave.ca
http://www.geocities.com/MotorCity/5939

1982 Coupe TURBO (473,150 km)
1984 4000s quattro (soon to be a rally car)
1986 4000s quattro (326,000 km) 
1982 Coupe (154,000) parts car

CEO of exam lastminute allniter rollthedice inc.