Hey, thanks for taking me back to school. At least I didn't paint stuff
flat black...
On 2/22/2015 5:26 PM, Jim Lux wrote:
On 2/20/15 4:19 PM, SPENCER wrote:
What type of material and/or what color paint should I use to reduce
heating from the sun
on my outdoor electronics?
white paint.
counter-intuitively
Shiny metal actually gets hotter in the sun than white or black paint.
That's because the metal has low emissivity, so even though the
absorption is low, it has even lower emission, so it doesn't radiate
the heat away as well. (this is why the seatbelt buckle, the chrome
on your car or a polished metal railing gets so hot in the sun)
polished metal is down in the 0.02-0.04 range (oxidized silver is 0.04)
paint is about 0.9, as are most substances (your IR thermometer
probably assumes e=0.9)
aluminum foil, for instance, reflects about 85% of the incident solar
radiation, so it absorbs 15%. But because it's emissivity is so low,
it doesn't radiate heat very well.. it gets hot in the sun.
White paint has an absorbtion around 75-85%, but has emissivity of
0.9. So while it absorbs a bit more than shiny metal, it easily
radiates it away.
It's called the A/E ratio...
http://contrails.iit.edu/DigitalCollection/1960/WADDTR60-773article08.pdf
The sort of dull aluminum paint might be OK, but I don't have any test
data.
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