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Re: [TowerTalk] remote tuner enclosure

To: towertalk@contesting.com
Subject: Re: [TowerTalk] remote tuner enclosure
From: Patrick Greenlee <patrick_g@windstream.net>
Date: Sun, 22 Feb 2015 22:11:13 -0600
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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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