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
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