[TowerTalk] polyrod

[Roger K8RI on Tower]

One could think of an object here on Earth as an antenna receiving energy
from the sun.  Since the sun is transmitting about 4 × 10**26 watts, it is
not difficult to understand why that Al plate got so hot.

Not just think of, but they actually work that way.
I've forgotten the number of watts per square foot/meter/yard, but it's a 
fair amount.

The reason a white object does not get as hot as a dark one is simply that
it reflects a large portion of light energy instead of absorbing it.  Also,
an object with more mass stores more energy.

It stores more jouls, just as in capacitance, but capacity does not 
translate into higher temperature. That is a function of the color.  OTOH 
that capacity represents energy so it takes longer to heat the massive 
object to a stable temperature and  it takes longer for the temperature to 
come down.  That is a good reason for concrete walls in solar heated homes. 
Thermal stability.  Surprisningly, Forrest Green seems to absorb more heat 
than black.

Imagine the temperature of that huge Aluminum plate had it been painted 
black or forrest green.
Even weating leather gloves I burnt my hands, but they provided enough 
protection I was able to drop the edge of the plate before the burns were 
serious.  32 square feet, 1" thick is 32/12=2.66 Cu feet of Aluminum. 
What's that weigh?

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com

>  Translated into desired
properties of fiberglass used as guy lines: white, thin rod with high
temperature resistance.

73, Keith NM5G

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Roger K8RI on Tower
Sent: Monday, May 02, 2005 10:35 PM
To: Tom Rauch; k3mm at comcast.net; towertalk at contesting.com
Subject: Re: [TowerTalk] polyrod

Just as a point of interest on color and heat.



In a glass covered solar heater using Forest Green as the color on the
heating element, if the water flow stops, I believe the resting temperature
of the element will be around 340 to 380 F.



I've seen bare aluminum plate 4' X 8' X 1" think (that's heavy!) that had
been left laying on the pavement in front of the shop where I used to work
get so hot that a cup of water thrown on it would hiss as it turned into
steam.  It was like throwing water onto a hot frying pan.



Roger Halstead (K8RI and ARRL 40 year Life Member) N833R - World's oldest
Debonair CD-2 www.rogerhalstead.com


_______________________________________________

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_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any 
questions and ask for Sherman, W2FLA.

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