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[Amps] oil vs distilled water cooling.

Subject: [Amps] oil vs distilled water cooling.
From: John Lyles <>
Date: Wed, 15 Apr 2015 21:57:07 -0600
List-post: <">>
##  so exactly what is the issue with oil vs distilled water ???   Distilled 
can be found in 4 litre jugs, cheap, at any grocery store.  To the best of my 
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 
it?s a moot point, since it?s a closed loop anyway.

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