[Milsurplus] GRC109/R-1004A arrived!

[J. Forster]

Here's a simple introduction:

http://en.wikipedia.org/wiki/Heat_transfer

Heat transfer can be complex (free convection and radiation especially),
and dramatically non-linear too (especially boiling).

I mostly studied it in the pre PC age, which required an understanding of
the principles, not just typing into a canned spreadsheet.

Best,

-John

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



> Thank you john. You and I seem to know what the other is talking about at
> least. :-)
>
> Sent from myTouch 4G
>
> ----- Reply message -----
> From: "J. Forster" <jfor at quikus.com>
> To: "bcarling at cfl.rr.com" <bcarling at cfl.rr.com>
> Cc: "Mike Morrow" <kk5f at arrl.net>, <milsurplus at mailman.qth.net>
> Subject: [Milsurplus] GRC109/R-1004A arrived!
> Date: Wed, Sep 14, 2011 2:39 pm
>
>
> 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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