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

Bob Camp lists at cq.nu
Thu Dec 24 20:32:14 UTC 2009


Hi

A heat pipe might work if the fluid had a sufficiently low boiling point. The rubidium isn't terribly tolerant of high temperatures, and I'm going to pick up some heat rise as I put it inside some baffles / shields. You need to find something that fits a fairly narrow window. 

I suspect that a recirculating water loop is a more practical approach to carry away the heat. It's got a pump to move the water, but the rest of it is fairly simple. 

Bob


On Dec 24, 2009, at 2:49 PM, Joe Gwinn wrote:

> 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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