[Milsurplus] GRC109/R-1004A arrived!

[bcarling@cfl.rr.com]

Someone must have propagated the fairly well about black heatsinks a long time ago then.

 By the way there is not much sunlight in a jungle unless you are in a clearing generally.

Sent from myTouch 4G

----- Reply message -----
From: "Mike Morrow" <kk5f at earthlink.net>
To: <milsurplus at mailman.qth.net>
Subject: [Milsurplus] GRC109/R-1004A arrived!
Date: Wed, Sep 14, 2011 2:05 pm


>Every piece of solid state power equipment I have ever used
>with a heat sink has it colored black.

There are likely many more heat sinks in natural metal finish
than there are painted (any color) sinks.  Heat sinks in air
are **convective** heat dissipation devices whose color is
completely irrelevant to the physical process.  Only in space
or other vacuum-like ambient conditions will *radiative* heat
transfer become significant.  And that requires very high
temperatures.

> I am fairly sure that the engineers who painted the grc109 boxes
> black did so for a reason.

There is NO positive consequence of ANY type from the black color
of the AN/GRC-109 components.  If exposed to sunlight like, er,
sometimes would have been the case in SE Asian jungles, the cases
will absorb much more heat from that exposure than they eliminate
by *radiative* heat transfer to ambient.

As John said, radiative heat transfer is a *negligible* portion of
the heat transfer process when the object in question is in contact
with other solids (conductive) and air (convective).  None of these
two grossly more significant heat transfer mechanisms are influenced
at all by the color of the object.  However, the heat load that the
conductive and convective processes must dissipate includes not only
the heat generated by the electronics, but also the heat from the
absorption of ambient sunlight aggravated by the black color.

The original RS-1 set upon which the AN/GRC-109 is based is black.
RS-1 is generally considered to have been designed as a clandestine
use radio set.  Black was probably as good a color as any other.
The US Army adopted it for ersatz use as the AN/GRC-109, and finally
bought the 1969 AN/GRC-109A for the same make-do use.  I doubt any
that engineer ever contemplated the color of the set.

Mike / KK5F
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