The thick graphite plates simply provide a large thermal mass that takes
longer to warm up and a lot longer to cool down than the thin metal plates.
Compare it your self sometime between 3-500Z's of both materials.
I believe the color of the metal plates is natural and not applied.
And Ive yet to see any black external anode tubes....unless the cooling
system failed.
Carl
KM1H
----- Original Message -----
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: <amps@contesting.com>
Sent: Sunday, December 19, 2010 12:15 AM
Subject: [Amps] FW: Fan for SB220
> Plates in radiation cooled power tubes are either coated with black carbon
> or made of graphite because black is a better radiator.
> 73
> Bill wa4lav
>
> ________________________________________
> From: Fuqua, Bill L
> Sent: Sunday, December 19, 2010 12:13 AM
> To: Adrian; amps@contesting.com
> Subject: RE: [Amps] Fan for SB220
>
> It ends up that the perfect black or any thing that absorbs radiation
> perfectly also radiates it perfectly.
> Goes to the theory of the black body radiation.
>
> To quote " Since a black body is a perfect absorber of radiant energy, by
> the laws of thermodynamics it must also be a perfect emitter of
> radiation."
> Quote from http://www.answers.com/topic/black-body
>
> 73
> Bill wa4lav
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf
> Of Adrian [vk4tux@bigpond.com]
> Sent: Saturday, December 18, 2010 5:31 PM
> To: amps@contesting.com
> Subject: Re: [Amps] Fan for SB220
>
> There seems to be a lot of confusion regarding heat transfer here. Black
> is not the the best colour for radiating heat, it does not radiate
> anything and that's what makes it black *.
>
> That also is why it is a good idea in the sb-220 tube cabinet to
> minimise reflected radiated heat back to the tubes. I have compared
> before and after temperatures on the mid tube outside envelope
> temperature and saw a 17 deg C drop after the inner cabinet was painted
> flat black on my sb-220
>
> Due to this *, black maintains a higher surface temperature making it
> more efficient with convection cooling (not radiated ) than other
> colours, heat transfer is dependent on the temperature difference
> between the two mediums involved with conduction and convection cooling.
>
> A black plate between the tubes would be effective to reduce radiated
> heat transfer between the two tubes, as it will absorb the radiated heat
> raising the material surface temperature, and releasing this heat with
> convection cooling from the fan, but I would be concerned with the
> effect on stray capacitance with its close proximity , and I'd like to
> keep stuff like that well away from the B+ in anycase.
>
> I say painting the tube surround black is a smart move, but forget about
> added divider plates.
> May cause more problems than it helps.
>
> Adrian ... vk4tux
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|