On Mon, Apr 05, 2010 at 12:15:45PM -0400, TexasRF@aol.com wrote:
> Larry, I wonder why your aversion to using water?
I can't speak for Larry, but have worked with very large water-cooled
mainframe computers. They needed some care and feeding to prevent algae
growth, and I don't doubt that IBM put a lot of time and effort into
designing hardware that wouldn't have corrosion and/or dissolution problems
with the water.
Water is just about the best solvent there is, and has the distinct
advantage of being non-flammable. Water-based solutions are, on the other
hand, pretty conductive, which isn't necessarily desirable in gear that
uses high voltages. There's a large and publicly-available body of work on
water-cooling.
I don't know how much info is available on oil cooling; it is flammable,
which isn't necessarily desirable, either: there _will_ be leaks, and
oil-resistant flexible seals cost a bit more than vanilla synthetic
flexible seals. You might be able to use one of the silicone oils, but they
pose some problems of their own, especially having to do with their extreme
slipperiness. Even so, DC-444 (Dow Corning 444) is good up to 444°F, which
is well above where you'll want to run tubes, is used as a heat transfer
medium in solar-heating systems, and doesn't eat rubber as far as I know.
One of the very nicest properties of water is its heat capacity: a _lot_ of
energy is required to get it to boil. Since the maximum seal temperature on
most EIMAC tubes I know of is above water's boiling point at 1 atm., water
cooling works very nicely. Vapor-phase cooling is even more efficient: you
actually get the water up to boiling, and _LOTS_ of energy is carried off
in those steam bubbles.
I don't know that oil has properties sufficiently similar that it can be
used safely in vapor-phase cooling and stay below the max. seal temp. I'd
be concerned about flash points and the like with very hot oil in any
event. Somehow I doubt that you'd like to run your amp inside a tub of
argon, or install CO2 bottles, just to ensure that you can prevent or stop
a fire if the oil decides to play up at you.
"SRI, OM; had to pull the fire-suppression bottles on the linear, and now
am running barefoot. VY 73, de ... ."
--
Mike Andrews, W5EGO
mikea@mikea.ath.cx
Tired old sysadmin
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