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Re: [Amps] liquid cooling

To: Larry <larry@w7iuv.com>
Subject: Re: [Amps] liquid cooling
From: Roger <sub1@rogerhalstead.com>
Date: Mon, 05 Apr 2010 16:28:46 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>

Larry wrote:
> The recent discussion on water cooling amp tubes got me thinking. Again. 
> (not a good thing)
>   
It sure got some others off on a tangent though.
> Basically I would like to play with liquid cooling but I can't/won't use 
> water.
Why.  It is the best, most reliable, cheapest, and most efficient liquid 
you will find for cooling.
>  While I was still working, I worked on a multi-kilowatt amplifier 
> that was oil cooled. It went into the avionics bay of an aircraft where 
> all the rest of the equipment was also oil cooled.
>   
Typically oil is used as an insulator along with the less than stellar 
cooling. It allows amplifiers to be made smaller and "some forms"*can* 
be self healing with arcs.
> As I recall, the oil looked and felt like mineral oil,
It most likely was one of the Silicones, probably 200 fluid. But...200 
fluid is sold under many names and over a very wide range of viscosities 
with various additives.
>  but I'm sure the 
> military wouldn't use something that common and cheap and low flash 
> point. At the time, I pulled up the MSDS for the oil but no longer have 
> it and of course I can't remember the numbers.
>
> K8CU talks about using ATF for cooling liquid here:
>   
Like 200 fluid ATF comes in many flavors both organic and inorganic 
(mostly Silicones)
> http://www.realhamradio.com/liquid-cooling.htm
>
> Unfortunately, there is no indication in the article that he or anyone 
> else actually used ATF. Now ATF contains sulphur compounds
Only the organic and not all of them contain sulfur compounds.
>  that eat 
> silver plating and cannot normally be used in things like dummy loads 
> because of this property. However, a set of heat exchangers used for 
> tube cooling would not have that problem.
>
> K8CU also mentions mineral oil and says it is not suitable due to the 
> low flash point. I have to wonder about that because for one I would 
> hope nothing in a system I would build would ever get hot enough to 
> worry about flash point and two,
The system *should* operate at less than 200C to 250C
>  it probably won't flash anyway due it 
> being in a closed system with little or no free air/oxygen.
>
>   
You could use car gas in a closed and purged system at multiples of its 
flash point, but at those temps for that fluid in a closed system the 
flash point would be the least of your worries.
> What I'm looking for is someone who has actually done liquid cooling 
> with something other than water. No, I have no interest in "flat earth" 
> theories, or what you think you remember from a thermodynamics class you 
> sat through 40 years ago. I want actual test results and operational 
> data from real world applications.
>
>   


Speaking from nearly 4 decades of working with liquid cooling including 
research with synthetic fluids:
Again: Why?

Look at the pro's and con's.

Water is the cheapest, most efficient, safest, easiest to use, and has 
the highest thermal transmission capabilities of any fluid you are going 
to find.

Organic and Inorganic fluids are expensive and really a pain in the 
backside if you ever have a spill. IOW you do not want to use them in 
your house. With organic fluids you may even run into code problems with 
using flammable liquids. 

There are fluids that have a high enough flash point to be used in a 
closed system, but they are no where near as efficient as water.  OTOH 
you could build a completely sealed amp, fill it with oil,  (think of 
all the sealing nightmares) and circulate the oil through a 
cooler/radiator and fan.

Yes, water has its negative aspects, but they are few compared to oil 
and most of those though of are either not applicable to cooling an amp, 
or are of a much lesser importance when compared to large systems. As 
some have noted water is the world's greatest/universal solvent. Only 
distilled and deionized water are essentially non conductive. They have 
a high enough *resistivity* to be called  insulators. BUT both have a 
strong affinity for ions.  You need a probe designed to measure 
resistivity in ohms per cubic centimeter and I doubt you will find many.

In large systems that run 24X7 with many RF generators and many hundreds 
of feet of copper and brass tubing and fittings the water has to be 
changed on a regular basis. In a system that only runs intermittently 
and scaled down to say a 5 or 10 gallon plastic or fiberglass 
reservoir,  using plastic tubing (Tygon) a low pressure system running a 
plastic or fiberglass pump with plastic hose barbs, it should run many 
months with no service other than monitoring the resistivity of the 
water.  BUT like any mechanical system there are parts subject to 
failure such as fans and pumps.  Using a CLEAN radiator and at at least 
10 gallons of water you'd only need a fan to cool the radiator which 
could be remotely mounted for a silent system.
Avoid the cheap pumps and coolers. It's unlikely you will even need a 
refrigeration unit.
It'll take a while to work out the kinks, but water is far superior to 
oil as a coolant.

Do not make the mistake of comparing liquid cooling with computers and 
amps.  Resistivity is not a problem with cooling computers, but 
condensation is. IF you use chilled coolant of any kind the amp (or 
computer) needs to be in an air conditioned environment with low 
humidity.  The minimum length of the plastic tubing between the anode 
and ground is important while lengths are only handy physical properties 
in computers.

73

Roger (K8RI)
> 73, Larry
>
> Larry - W7IUV
> DN07dg - central WA
> http://w7iuv.com
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