On 16 Apr 2015, at 17:01, amps-request@contesting.com wrote:
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Today's Topics:
1. oil vs distilled water cooling. (John Lyles)
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Message: 1
Date: Wed, 15 Apr 2015 21:57:07 -0600
From: John Lyles <jtml@losalamos.com>
To: amps@contesting.com
Subject: [Amps] oil vs distilled water cooling.
Message-ID: <552F3313.2080307@losalamos.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
## so exactly what is the issue with oil vs distilled water ??? Distilled
water
can be found in 4 litre jugs, cheap, at any grocery store. To the best of my
knowledge,
distilled water will extract heat a lot faster / better than oil. I only saw
1-2 small tubes in the
entire Eimac catalog that used oil cooling. All their big commercial broadcast
tubes are either
air, or water, or vapor phase cooled tubes. Or multi-phase cooled.... which is
a combo of
water cooled and vapour phase cooling.
All of the amplifiers I design and use at work are water cooled, some
flowing water and some multiphase, or hypervapotron mode, which is the
same thing but a trademark. Its not a tough problem to crack, and I'm
dealing with considerable HV. I studied the RCA, Eimac and Thomson
recommendations some years ago, and use a common set of specifications.
Keep the DC leakage current in the hoses < 500 uA per hose. So for
whatever resistivity is maintained, the hose diameter and length is
designed for this current (resistance) at the maximum plate voltage to
be used. DI water is closed loop cooled, as its New Mexico and we cannot
waste water. This complicates things with heat exchangers and secondary
loops with cooling towers. Since the water is recycled, we have to watch
the ph and the dissolved oxygen level as well. For < 5 kV DC I think the
requirements are much less difficult to meet.
Now, adding an ionic additive like water wetter is risky for a pure DI
or distilled water system. One reply said the typical content is:
DiIsoPropyl Alcohol Ether 1-4.9%
TriIsopropyl Alcohol Diether 1-4.9%
Sodium Molybdate 1-4.9%
Tolyltriazole 1-3%
PolySiloxane Polymer
That third one is a good corrosion inhibitor. I use the same molybdate
as an ionic additive, that when put in solution with pure water, makes
an excellent dummy load. The amount is about 0.5% by weight, and I use
what are called water column loads. These are essentially
multiwavelength long coaxial cylinders with a shorted center conductor
at the far end. They contain a way for this solution to flow through,
and if I use pure water the mismatch is terrible, like 1 dB RL. When I
add the 0.5%, the match becomes 20 dB RL at a specific frequency. So a
tiny bit of molybdate makes a huge change in RF loss. I have also
noticed that it makes a large difference in the DC conductivity of the
solution. My best soup is 530 microsiemens/cm^2. With just a few hundred
cc dumped into a system with several hundred gallons flowing will change
this value by a factor or 2 or more.
I would be wary of doping the distilled water with these chemicals
without doing an experiment first.
## last year, I tested distilled water vs tap water with just a fluke 87
dvm. The
dc resistance of distilled water is sky high compared to tap water. Distilled
water is
a superb insulator. Dunno what happens to the dc resistance once water
wetter is
added to the distilled water. I should re-run the test. For a tube cooling
application
it?s a moot point, since it?s a closed loop anyway.
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