[time-nuts] Cheap Rubidium (heatpipe cooling for)

Don Latham djl at montana.com
Thu Dec 24 20:27:14 UTC 2009


Are we getting close to a Stirling engine running as a frig?
Don
Joe Gwinn
> A dodge occurs to me - a homebrew heat pipe:
> <http://en.wikipedia.org/wiki/Heat_pipe>.
>
> Make the cold plate of copper, to which is soldered a meandering
> piece of copper tubing, which tubing is also soldered to a copper
> radiator plate that is above the coldplate, forming a closed loop
> with a fill tube attached by a T.  Braze all tubing connections, as
> for freon refrigeration systems.  (Soft solder is too porous to work
> for the joints, but is OK for attaching tubes to plates.)
>
> Insulate the two tubes running between coldplate and radiator plate
> from one another.
>
> Put enough working fluid into the system to fill the tubing that is
> soldered to the coldplate, but no more.  Warm the system up so the
> vapor drives all the air out, pinch the fill tube off and fold it
> back, and braze the end shut.   (It's not critical to get absolutely
> all the air out.)
>
> Making the radiator plate be above the coldplate (the boiler)
> implements what amounts to an oldtime two-pipe water vapor heating
> plant.  Vapor goes up one pipe, condensed fluid returns via the
> other.  I lived in a house with such a system.  The difference
> between a vapor plant and a steam plant is pressure:  the vapor plant
> runs below atmospheric pressure, while the steam plant runs at or
> slightly above.
>
> Make sure that things are arranged so the returning fluid does not
> pool anywhere but in the coldplate, or the heat pipe will bang like
> an old steam heating system.
>
> There is a brazing filler metal intended for copper-to-copper joints
> that is widely used for freon systems:
> <http://www.uniweld.com/catalog/alloys/silver_brazing_alloys/phos_copper.htm>.
> The zero silver phos stuff is adequate, cheap and widely available.
> While copper-to-copper needs no flux, copper-to-brass does, so also
> get the flux.  Plumbing supply houses and welding equipment stores
> are likely sources.  You will also need a torch or pair of torches
> able to raise the tubing joints to an orange heat in a reasonable
> length of time.
>
> Depending on the chosen working fluid, the cold plate temperature
> will not rise above the boiling point of the fluid unless the system
> is too small (in radiator heat removal capacity) to easily handle the
> 10 or 20 thermal watts that are passing through.
>
> What fluid to use?  Anything common and thermally stable that does
> not attack copper.  Alcohol (methyl or ethyl) and water are common
> choices, as are the various freons.  I bet acetone would also work.
> Anyway, one controls the coldplate temperature by a combination of
> choice of working fluid and internal pressure.
>
>
> I have seen commercially made heat pipes for cooling Intel CPUs
> advertised, but I don't know that these units can be adapted.
>
> Anyway, a heat pipe system will stabilize the coldplate temperature
> fairly accurately despite variations in thermal load, has no moving
> or electrical parts, and may be sufficient by itself.  If not
> sufficient, it can be used as the outer stage in a two-stage ovening
> scheme.
>
>
> Joe Gwinn
>
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-- 
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com





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