[TowerTalk] remote tuner enclosure

[Patrick Greenlee]

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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