[Milsurplus] GRC109/R-1004A arrived!

[J. Forster]

It's an urban legent, based on a lack of understanding of thermodynamics.

Probably helped by the marketing people. The biggest reason for black
anodizing or painting is to cover up what's underneath. It's much easier
to get a flat black finish repeatably than say a golden one.

Oh, and it probably looks "more prefessional" too.

In fact, paint of any color, would reduce heat flow by adding thermal
impedance. However, the paint impedance would be small in comparison to
the film coefficient, unless there was fast air flow from a fan or
something.

-John

===============


> 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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